Unmanned Systems
As drone aircraft evolve beyond traditional ISR applications to a combination of ISR and strike capabilities, the potential sub-applications of UAVs continue to expand along with the related need for high accuracy stabilization, navigation, advanced flight control, and faster data communication.
Signal Chains
(3)
Interactive Signal Chains

Reference Designs
CN0352


The demand for Lithium ion (Li-ion) batteries is high for use in both low power and high power applications, such as laptop computers, mobile phones, portable wireless terminals, as well as hybrid electric vehicles/all-electric vehicles (HEV/EV). Li-ion batteries therefore require accurate and reliable test systems.
The battery test system in Figure 1 is composed of multiple input/output boards (EVAL-CN0352-EB1Z_IO) for handling the charging and discharging process, an MCU board (EVAL- CN0352-EB1Z_MCU) for battery data acquisition, testing, monitoring, and temperature management, and a backplane base board (EVAL-CN0352-EB1Z_BAS) that provides the signal interconnections between the MCU board and the multiple input/output boards.
The circuit uses the ADP5065 fast charging battery manager for flexible, efficient, high stability charging control with low cost, small printed circuit board (PCB) area, and ease of use compared to traditional discrete solutions.
Highly integrated precision data acquisition and processing is provided by the ADuCM360 precision analog microcontroller. The ADuCM360 acquires the battery voltage, current, and temperature. A high precision analog-to-digital converter (ADC), digital-to-analog converter (DAC), and an on-chip microcontroller allows completely self-contained control of the charging and discharging process.
The analog front end is fully differential with high CMRR and excellent immunity to both common-mode and ground noise caused by large currents generated during the charge and discharge cycles.
The number of channels can easily be expanded to further reduce testing time and cost per battery.
Applicable Parts
ADP5065
Fast Charge Battery Management with Power Path and USB Compatibility
ADG715
CMOS, Low Voltage, I2C Compatible Interface, Serially Controlled, Octal SPST Switches
AD8601
DigiTrim™ RRIO Single Op Amp with Very Low Offset Voltage
AD8237
Micropower, Zero Drift, True Rail-to-Rail Instrumentation Amplifier
AD8275
G = 0.2, Level Translation, 16-Bit ADC Driver
AD8276
Low Power, Wide Supply Range, Low Cost Unity-Gain Difference Amplifier
ADuCM362
Low Power, Precision Analog Microcontroller with Dual Sigma-Delta ADCs, ARM Cortex-M3
ADuCM363
Low Power, Precision Analog Microcontroller with Single Sigma-Delta ADC, ARM Cortex-M3
Applications
CN0276


The circuit has an innovative resolver rotor driver circuit that has two modes of operation: high performance and low power. In the high performance state, the system operates on a single 12 V supply and can supply 6.4 V rms (18 V p-p) to the resolver. In the low power state, the system operates on a single 6 V supply and can supply 3.2 V rms (9.2 V p-p) to the resolver, with less than 100 mA of current consumption. Active filtering is provided in both the driver and receiver to minimize the effects of quantization noise.
The maximum tracking rate of the RDC is 3125 rps in the 10-bit mode (resolution = 21 arc min) and 156.25 rps in the 16-bit mode (resolution = 19.8 arc sec).
Applicable Parts
AD8692
Low Cost, Low Noise, Dual CMOS Rail-to-Rail Output Operational Amplifier
AD2S1210
Variable Resolution, 10-Bit to 16-Bit R/D Converter with Reference Oscillator
ADG1611
1 Ω Typical On Resistance, ±5 V, +12 V, +5 V, and +3.3 V Quad SPST Switches
ADG1612
1 Ω Typical On Resistance, ±5 V, +12 V, +5 V, and +3.3 V Quad SPST Switches
ADM6328
Ultralow Power, 3-Lead, SOT-23, Microprocessor Reset Circuit, Active-Low Open-Drain Output, 0.5 µA Supply Current
ADP7104
20 V, 500 mA, Low Noise, CMOS LDO
AD8397
Rail-to-Rail, High Output Current Amplifier
AD8694
Low Cost, Low Noise, CMOS Rail-to-Rail Output Quad Op Amp
Applications
Building Technology
- Building Control and Automation
CN0288

The circuit shown in Figure 1 is a complete adjustment-free linear variable differential transformer (LVDT) signal conditioning circuit. This circuit can accurately measure linear displacement (position).
The LVDT is a highly reliable sensor because the magnetic core can move without friction and does not touch the inside of the tube. Therefore, LVDTs are suitable for flight control feedback systems, position feedback in servomechanisms, automated measurement in machine tools, and many other industrial and scientific electromechanical applications where long term reliability is important.
This circuit uses the AD598 LVDT signal conditioner that contains a sine wave oscillator and a power amplifier to generate the excitation signals that drive the primary side of the LVDT. The AD598 also converts the secondary output into a dc voltage. The AD8615 rail-to-rail amplifier buffers the output of the AD598 and drives a low power 12-bit successive approximation analog-to-digital converter (ADC). The system has a dynamic range of 82 dB and a system bandwidth of 250 Hz, making it ideal for precision industrial position and gauging applications.
The signal conditioning circuitry of the system consumes only 15 mA of current from the ±15 V supply and 3 mA from the +5 V supply, making this ideal for remote applications. The circuit can operate a remote LVDT from up to 300 feet away, and the output can drive up to 1000 feet.
This circuit note discusses basic LVDT theory of operation and the design steps used to optimize the circuit shown in Figure 1 for a chosen bandwidth, including noise analysis and component selection considerations.

Applicable Parts
Applications
Building Technology
- Building Control and Automation
CN0301

The LVDT is a highly reliable sensor because the magnetic core can move without friction and does not touch the inside of the tube. Therefore, LVDTs are suitable for flight control feedback systems, position feedback in servomechanisms, automated measurement in machine tools, and many other industrial and scientific electromechanical applications where long term reliability is important.
This circuit uses the AD698 LVDT signal conditioner that contains a sine wave oscillator and a power amplifier to generate the excitation signals that drive the primary side of the LVDT. The AD698 also converts the secondary output into a dc voltage. The AD8615 rail-to-rail amplifier buffers the output of the AD698 and drives a low power 12-bit successive approximation analog-to-digital converter (ADC). The system has a dynamic range of 82 dB and a system bandwidth of 250 Hz, making it ideal for precision industrial position and gauging applications.
The signal conditioning circuitry of the system consumes only 15 mA of current from the ±15 V supply and 3 mA from the +5 V supply.
This circuit note discusses basic LVDT theory of operation and the design steps used to optimize the circuit shown in Figure 1 for a chosen bandwidth, including noise analysis and component selection considerations.

Figure 1. Universal LVDT Signal Conditioning Circuit (Simplified Schematic: All Connections and Decoupling Not Shown)
Applicable Parts
Applications
Building Technology
- Building Control and Automation
CN0374

The circuit shown in Figure 1 precisely converts a 400 MHz to 6 GHz RF input signal to its corresponding digital magnitude and digital phase. The signal chain achieves 0° to 360° of phase measurement with 1° of accuracy at 900 MHz. The circuit uses a high performance quadrature demodulator, a dual differential amplifier, and a dual differential 16-bit, 1 MSPS successive approximation analog-to-digital converter (SAR ADC).

Figure 1. Simplified Receiver Subsystem for Magnitude and Phase Measurements(All Connections and Decoupling Not Shown)
Applicable Parts
Applications
Communications
CN0371

The circuit shown in Figure 1 is a complete linear variable differential transformer (LVDT) signal conditioning circuit that can accurately measure linear position or linear displacement from a mechanical reference. Synchronous demodulation in the analog domain is used to extract the position information and provides immunity to external noise. A 24-bit, Σ-Δ analog-to-digital converter (ADC) digitizes the position output for high accuracy.
LVDTs utilize electromagnetic coupling between the movable core and the coil assembly. This contactless (and hence frictionless) operation is a primary reason for why they are widely used in aerospace, process controls, robotics, nuclear, chemical plants, hydraulics, power turbines, and other applications where operating environments can be hostile and long life and high reliability are required.
The entire circuit, including the LVDT excitation signal, consumes only 10 mW of power. The circuit excitation frequency and output data rates are SPI programmable. The system has a programmable bandwidth vs. dynamic range trade-off. It supports bandwidths of over 1 kHz, and at a bandwidth of 20 Hz, the circuit has a dynamic range of 100 dB, making it ideal for precision industrial position and gauging applications.

Applicable Parts
Applications
Building Technology
- Building Control and Automation
CN0292

The circuit acquires and digitizes standard industrial signal levels of ±5 V, ±10 V, 0 V to 10 V, and 0 mA to 20 mA. The input buffers also provide overvoltage protection, thereby eliminating the leakage errors associated with conventional Schottky diode protection circuits.
Applications for the circuit include process control (PLC/DCS modules), battery testing, scientific multichannel instrumentation, and chromatography.

Figure 1. Functional Block Diagram of 4-Channel Data Acquisition System (Simplified Schematic: All Connections and Decoupling Not Shown)
Applicable Parts
AD7176-2
24-Bit, 250 kSPS Sigma Delta ADC with 20 µs Settling
ADR4550
Ultra-Low-Noise, High-Accuracy 5.0V Voltage Reference
ADA4096-4
30 V, Micropower, Overvoltage Protection, Rail-to-Rail Input/Output Quad Op Amplifier
ADG1204
Low Capacitance, Low Charge Injection, ±15 V/+12 V, 4:1 iCMOS Multiplexer
ADP1720
50 mA, High Voltage, Micropower Linear Regulator
AD8475
Precision, Selectable Gain, Fully Differential Funnel Amplifier
ADUM3471
Isolated Switching Regulators (3/1 Channel Directionality)
ADP7102
20 V, 300 mA, Low Noise, CMOS LDO
ADA4898-1
High Voltage, Low Noise, Low Distortion, Unity Gain Stable, High Speed Op Amp
ADP7182
–28 V, −200 mA, Low Noise, Linear Regulator
AD7173-8
Low Power, 8-/16-Channel, 31.25 kSPS, 24-Bit, Highly Integrated Sigma-Delta ADC
AD7172-2
Low Power, 24-Bit, 31.25 kSPS, Sigma-Delta ADC with True Rail-to-Rail Buffers
AD7172-4
Low Power, with 4- or 8-channel, 24-bit, 31.25 kSPS, Sigma-Delta ADC with True Rail-to-Rail Buffers
AD7177-2
32-Bit, 10 kSPS, Sigma-Delta ADC with 100 µs Settling and True Rail-to-Rail Buffers
AD7175-2
24-Bit, 250 kSPS, Sigma-Delta ADC with 20 µs Settling and True Rail-to-Rail Buffers
AD7175-8
24-Bit, 8-/16-Channel, 250 kSPS, Sigma-Delta ADC with True Rail-to-Rail Buffers
Applications
CN0317

Common applications of RDCs are in automotive and industrial markets to provide motor shaft position and/or velocity feedback.
Figure 1. High Current Buffer Using the AD8397 for the AD2S1210 RDC Excitation Signal Output (Simplified Schematic: Decoupling and All Connections Not Shown)
Applicable Parts
Applications
CN0240

The AD629 amplifier accurately measures and buffers (G = 1) a
small differential input voltage and rejects large positive
common-mode voltages up to 270 V.
The dual AD8622 is used to amplify the output of the AD629 by a factor of 100. The AD8475 funnel amplifier attenuates the signal (G = 0.4), converts it from single-ended to differential, and level shifts the signal to satisfy the analog input voltage range of the AD7170 sigma-delta ADC.
Galvanic isolation is provided by the ADuM5402 quad channel isolator. This is not only for protection but also to isolate the
downstream circuitry from the high common-mode voltage. In addition to isolating the output data, the ADuM5402 digital isolator can supply isolated +5.0 V for the circuit.
The measurement result from the AD7170 is provided as a
digital code utilizing a simple 2-wire, SPI-compatible serial
interface.
This combination of parts provides an accurate high voltage positive and negative rail current sense solution with a small component count, low cost, and low power.
Figure 1. High Common-Mode Voltage Bidirectional Isolated Current Monitor (All Connections and Decoupling Not Shown)
Applicable Parts
AD629
High Common-Mode Voltage, Difference Amplifier
ADUM5402
Quad-Channel, 2.5 kV Isolators with Integrated DC-to-DC Converter (2/2 channel directionality)
ADR435
Ultralow Noise XFET® Voltage References with Current Sink and Source Capability
AD8622
Low Power, Low Noise, Low Bias Current, Precision Dual RRO Op Amp
AD7170
12-Bit Low Power Σ−Δ ADC
AD8475
Precision, Selectable Gain, Fully Differential Funnel Amplifier
Applications
CN0254

Applicable Parts
AD8605
Precision, Low Noise, CMOS, RRIO Op Amp (single)
AD8609
Precision Quad MicroPower Rail-to-Rail Input/Output Amplifier
AD7689
16-Bit, 8-Channel,250 kSPS PulSAR ADC
ADUM3471
Isolated Switching Regulators (3/1 Channel Directionality)
ADP3336
Small, Adjustable Output, 500 mA anyCAP® Low Dropout Regulator
AD8608
Low Noise, CMOS, Rail-to-Rail, Input/Output Precision Quad Op Amp
Applications
CN0190

The module shown in Figure 1 is a reference solution for multivoltage power systems. The design can easily be adapted to customer requirements and provides the most popular system voltages. The circuit uses an optimum combination of switching and linear regulators to provide an overall efficiency of approximately 78% when the outputs are fully loaded. Output power delivered under full load is approximately 25 W.
Applicable Parts
ADCMP670
Dual Low Power 1.5% Comparator With 400 mV Reference
ADM1178
Hot Swap Controller and Digital Power Monitor with ALERTB Output
ADP1864
Constant Frequency Current-Mode Step-Down DC-to-DC Controller in TSOT
ADM1066
Super Sequencer® with Margining Control and Auxiliary ADC Inputs
ADP1741
2 A, Low VIN, Dropout, CMOS Linear Regulator
ADP121
150 mA, Low Quiescent Current, CMOS Linear Regulator in 5-Lead TSOT or 4-Ball WLCSP
ADP2108
Compact, 600 mA, 3 MHz, Step-Down DC-to-DC Converter
ADP1613
650 kHz /1.3 MHz Step-Up PWM DC-to-DC Switching Converter with 2.0 A Current Limit
ADP2114
Configurable, Dual 2 A/Single 4 A, Synchronous Step-Down DC-to-DC Regulator
ADP1872
Synchronous Current-Mode Buck Controller with Constant On-time and 0.6 V Reference Voltage
ADP151
Ultra Low Noise, 200 mA CMOS Linear Regulator
ADP2300
1.2 A, 20 V, 700 kHz Nonsynchronous Step-down Switching Regulator
ADP2301
1.2 A, 20 V, 1.4 MHz non-synchronous step-down switching regulator
ADM1170
1.6 V to 16.5 V Hot Swap Controller
AD628
High Common-Mode Voltage, Programmable Gain Difference Amplifier
ADCMP350
Comparator & 0.6V Reference in 4-SC70 w/ Open-Drain Active-Low Output
Applications
CN0218

Figure 1: High Common-Mode Voltage Current Monitor (All Connections and Decoupling Not Shown)
The AD8212 accurately amplifies a small differential input voltage in the presence of large positive common-mode voltages greater than 500 V when used in conjunction with an external PNP transistor.
Galvanic isolation is provided by the ADuM5402 quad channel isolator. This is not only for protection but to isolate the downstream circuitry from the high common-mode voltage. In addition to isolating the output data, the ADuM5402 digital isolator can also supply isolated +3.3 V for the circuit.
The measurement result from the AD7171 is provided as a digital code utilizing a simple 2-wire, SPI-compatible serial interface.
This combination of parts provides an accurate high voltage positive rail current sense solution with a small component count, low cost, and low power.
Applicable Parts
Applications
CN0196

Modern microprocessors and microconverters are generally low power and operate on low supply voltages. Source and sink current for 2.5 V CMOS logic outputs ranges from μA to mA . Driving an H-bridge switching 12 V with a 4 A peak current requires the use of carefully selected interface and level translation components, especially if low jitter is needed.
The ADG787 is a low voltage CMOS device that contains two
independently selectable single-pole double-throw (SPDT)
switches. With a 5 V dc power supply, a voltage as low as 2 V
is a valid high input logic voltage. Therefore, the ADG787
provides appropriate level translation from the 2.5 V controlling
signal to the 5 V logic level needed to drive the ADuM7234
half-bridge driver.
The ADuM7234 is an isolated, half-bridge gate driver that
employs Analog Devices’ iCoupler® technology to provide
independent and isolated high-side and low-side outputs
making it possible to use N-channel MOSFETs exclusively in
the H-bridge. There are several benefits in using N-channel
MOSFETs: N-channel MOSFETs typically have one third of the
on resistance of P-channel MOSFETs and higher maximum
current; they switch faster, thereby reducing power dissipation;
and the rise time and fall time is symmetrical.
The 4 A peak drive current of the ADuM7234 ensures that the
power MOSFETs can switch on and off very fast, thereby
minimizing the power dissipation in the H-bridge stage. The
maximum drive current of the H-bridge in this circuit can be
up to 85 A, which is limited by the maximum allowable
MOSFET current.
The ADuC7061 is a low power, ARM7 based precision analog microcontroller with integrated pulse width modulated (PWM) controllers that have outputs that can be configured to drive an H-bridge after suitable level translation and conditioning.
Figure 1. H-Bridge Using ADuM7234 Isolated Half-bridge Driver (Simplified Schematic: All Connections and Decoupling Not Shown)
Applicable Parts
ADUM3100
Digital Isolator, Enhanced System-Level ESD Reliability
ADUC7061
Low-Power, Precision Analog Microcontroller, Dual Σ-Δ ADCs, Flash/EE, ARM7TDMI
ADUM7234
Isolated Precision Half-Bridge Driver, 4 A Output
ADCMP350
Comparator & 0.6V Reference in 4-SC70 w/ Open-Drain Active-Low Output
ADP1720
50 mA, High Voltage, Micropower Linear Regulator
ADG787
2.5 Ω CMOS Low Power Dual 2:1 Mux/Demux USB 1.1 Switch
Applications
CN0213

The analog front-end circuit shown in Figure 1 is optimized for high precision and high common-mode rejection ratio (CMRR) when processing these types of industrial-level signals.
Figure 1. High Performance Analog Front End for Process Control (Simplified Schematic: All Connections and Decoupling Not Shown)
The circuit level shifts and attenuates the signals so they are compatible with the input range requirements of most modern single-supply SAR ADCs, such as the AD7685 high performance 16-bit 250 kSPS PulSAR® ADC.
With an 18 V p-p input signal, the circuit achieves approximately 105 dB common-mode rejection (CMR) at 100 Hz and 80 dB CMR at 5 kHz.
High precision, high input impedance, and high CMR are provided by the AD8226 instrumentation amplifier. For high precision applications, a high input impedance is required to minimize system gain errors and also to achieve good CMR. The AD8226 gain is resistor-programmable from 1 to 1000.
A resistive level shifter/attenuator stage directly on the input would inevitably degrade CMR performance due to the mismatch between the resistors. The AD8226 provides the excellent CMR required for both small signal and large signal inputs. The AD8275 level shifter/attenuator/driver performs the attenuation and level shifting function in the circuit, without any need for external components.
Traditionally, sigma-delta ADCs have been used in high resolution measurement systems because signal bandwidths are quite low, and the sigma-delta architecture provides excellent noise performance at low update rates. However, there is an increased trend for higher update rates, especially in multichannel systems, to allow faster per-channel update, or for increased channel density. In such cases a high performance SAR ADC is a good alternative. The circuit shown in Figure 1 uses the AD7685 250 kSPS 16 bit ADC, with the AD8226 high performance in-amp, and the AD8275 attenuator/level shifter amplifier implemented as a complete system solution without the need for any external components.
Applicable Parts
AD7685
16-Bit, 250 kSPS PulSAR® ADC in MSOP/QFN
AD8226
Wide Supply Range, Rail-to-Rail Output Instrumentation Amplifier
AD8275
G = 0.2, Level Translation, 16-Bit ADC Driver
ADP1720
50 mA, High Voltage, Micropower Linear Regulator
ADR439
Ultralow Noise XFET® 4.5V Voltage Reference w/Current Sink and Source Capability
Applications
CN0209

The circuit shown in Figure 1 provides a fully programmable universal analog front end (AFE) for process control applications. The following inputs are supported: 2-, 3-, and 4- wire RTD configurations, thermocouple inputs with cold junction compensation, unipolar and bipolar input voltages, and 4 mA-to-20 mA inputs.
Today, many analog input modules use wire links (jumpers) to configure the customer input requirements. This requires time, knowledge, and manual intervention to configure and reconfigure the input. This circuit provides a software controllable switch to configure the modes along with a constant current source to excite the RTD. The circuit is also reconfigurable to set common-mode voltages for the thermocouple configuration. A differential amplifier is used to condition the analog input voltage range to the Σ-Δ ADC. The circuit provides industry-leading performance and cost.
Because of the voltage gain provided by the AD8676 and AD8275, the design is particularly suitable for small signal inputs, all types of RTDs, or thermocouples.
The AD7193 is a 24-bit Σ-Δ ADC that can be configured to have four differential inputs or eight pseudo differential inputs. The ADuM1400 and ADuM1401 provide all the necessary signal isolation between the microcontroller and the ADC. The circuit also includes standard external protection and is compliant with the IEC 61000 specifications.
Figure 1. Universal Programmable Analog Front End for Process Control Applications (Simplified Schematic: All Connections and Decoupling Not Shown)
Applicable Parts
AD8676
Ultra Precision, 36 V, 2.8 nV/√Hz Dual RRO Op Amp
ADG442
LC2MOS Quad SPST Switch
AD8275
G = 0.2, Level Translation, 16-Bit ADC Driver
ADT7310
±0.5°C Accurate, 16-Bit Digital SPI Temperature Sensor
AD7193
4-Channel, 4.8 kHz, Ultralow Noise, 24-Bit Sigma-Delta ADC with PGA
ADG1414
9.5 Ω RON ±15 V/+12 V/±5 V iCMOS Serially-Controlled Octal SPST Switches
ADUM1401
Quad-Channel Digital Isolator (3/1 Channel Directionality)
ADUM1400
Quad-Channel Digital Isolator (4/0 Channel Directionality)
ADP1720
50 mA, High Voltage, Micropower Linear Regulator
REF194
4.5V Precision Micropower, Low Dropout, Low Voltage Reference
AD8617
Low Cost Micropower, Low Noise CMOS RRIO Dual Op Amp
Applications
CN0237

Power dissipation of the ADA4940-1 in the circuit is typically 6.25 mW. The 18-bit, 1 MSPS AD7982 ADC consumes only 7 mW at 1 MSPS. This power also scales with the throughput. The ADR435 consumes only 4.7 mW, making the total power dissipated by the system less than 18 mW.
Figure 1. High Performance 18-Bit Differential ADC Driver (Simplified Schematic: All Connections and Decoupling Not Shown)
Applicable Parts
Applications
CN0187

The ADL5502 is a mean-responding (true rms) power detector
in combination with an envelope detector to accurately
determine the crest factor (CF) of a modulated signal. It can be
used in high frequency receiver and transmitter signal chains
from 450 MHz to 6 GHz with envelope bandwidths over 10 MHz.
The peak-hold function allows the capture of short peaks in the
envelope with lower sampling rate ADCs. Total current
consumption is only 3 mA @ 3 V.
The ADA4891-4 is a high speed, quad, CMOS amplifier that
offers high performance at a low cost. Current consumption is
only 4.4 mA/amplifier at 3 V. The amplifier features true singlesupply
capability, with an input voltage range that extends 300 mV
below the negative rail. The rail-to-rail output stage enables
the output to swing to within 50 mV of each rail, ensuring
maximum dynamic range. Low distortion and fast settling time
makes it ideal for this application.
The AD7266 is a dual, 12-bit, high speed, low power, successive approximation ADC that operates from a single 2.7 V to 5.25 V power supply and features sampling rates up to 2 MSPS. The device contains two ADCs, each preceded by a 3-channel multiplexer, and a low noise, wide bandwidth track-and-hold
amplifier that can handle input frequencies in excess of 30 MHz.
Current consumption is only 3 mA at 3 V. It also contains an
internal 2.5 V reference.
The circuit operates on a single +3.3 V supply from the
ADP121, a low quiescent current, low dropout, linear regulator
that operates from 2.3 V to 5.5 V and provides up to 150 mA
of output current. The low 135 mV dropout voltage at 150 mA
load improves efficiency and allows operation over a wide input
voltage range. The low 30 μA of quiescent current at full load
makes the ADP121 ideal for battery-operated portable equipment.
The ADP121 is available in output voltages ranging from 1.2 V to 3.3 V. The parts are optimized for stable operation with small 1 μF ceramic output capacitors. The ADP121 delivers good transient performance with minimal board area. Short-circuit protection and thermal overload protection circuits prevent damage in adverse conditions. The ADP121 is available in tiny 5-lead TSOT and 4-ball, 0.4 mm pitch halidefree WLCSP packages and utilizes the smallest footprint solution to meet a variety of portable applications.
Figure 1. High Speed, Low Power, Crest Factor, Peak, and RMS Power Measurement System (Simplified Schematic: All connections and Decoupling Not Shown)
Applicable Parts
ADP121
150 mA, Low Quiescent Current, CMOS Linear Regulator in 5-Lead TSOT or 4-Ball WLCSP
ADL5502
450 MHz TO 6000 MHz Crest Factor Detector
ADA4891-4
Low Cost CMOS, High Speed, Rail-to-Rail Amplifier (Quad)
AD7266
Differential/Single-Ended Input, Dual, Simultaneous Sampling, 2 MSPS, 12-Bit, 3-Channel SAR A/D Converter
Applications
CN0180

Whereas suitable interface circuits can be designed using resistor networks and dual op amps, errors in the ratio matching of the resistors, and between the amplifiers, produce errors at the final output. Achieving the required output phase matching and settling time can be a challenge, especially at low power levels.
The circuit shown in Figure 1 uses the AD8475 differential funnel amplifier to perform attenuation, level shifting, and conversion to differential without the need for any external components. The ac and dc performances are compatible with those of the 18-bit, 1 MSPS AD7982 PulSAR® ADC and other 16- and 18-bit members of the family, which have sampling rates up to 4 MSPS.
The AD8475 is a fully differential attenuating amplifier with integrated precision thin film gain setting resistors. It provides precision attenuation (by 0.4× or 0.8×), common-mode level shifting, and single-ended-to-differential conversion along with input overvoltage protection. Power dissipation on a single 5 V supply is only 15 mW. The 18-bit, 1 MSPS AD7982 consumes only 7 mW, which is 30× lower than competitive ADCs. The total power dissipated by the combination is only 22 mW.
Applicable Parts
Applications
CN0130

This product is used primarily in the automatic test equipment (ATE) industry as the power supply that drives the device under test (DUT). As such, there are many different requirements placed on the DPS, including voltage and current specifications (depending on the type of DUT it will drive), and other factors, such as stability, accuracy, etc.
As a device power supply, it is of utmost importance that the AD5560 can deliver the voltage and currents required by the DUT in a timely manner.
The AD5560 is designed to achieve a peak-to-peak voltage span of 25 V that can be placed anywhere within the range of −22 V to +25 V, limited by the maximum allowable voltage of |AVDD − AVSS| ≤ 33 V.
In addition, the current range that the AD5560 can deliver can be as high as ±1.2 A. Note that 1.2 A isn’t practical at the higher output voltages because of the power dissipation limitations of the package.
The 1.2 A capability is primarily intended for supplying a low voltage rail no greater than approximately 3.5 V, but this depends greatly on the cooling abilities and other conditions. Therefore, in reviewing the voltage/current requirements, many factors need to be taken into account, such as headroom, footroom, power dissipation under worst case conditions, supply rails, thermal performance, etc.
This circuit is designed to deliver three DUT rails:
The selection of components and configuration of the circuit will be tailored specifically for the above combinations.
For alternative use or just for more detailed information on the part itself, refer to the AD5560 data sheet.
Applicable Parts
Applications
CN0274

The 3-axis accelerometer controls the high-side switch by monitoring the acceleration in three axes and closes or opens
the switch depending on the presence or absence of motion.
The ADXL362 is an ultralow power, 3-axis accelerometer that consumes less than 100 nA in wake-up mode. Unlike accelerometers that use power duty cycling to achieve low power consumption, the ADXL362 does not alias input signals by under sampling; it samples continuously at all data rates. There is also an on-chip, 12-bit temperature sensor accurate to ±0.5°.
The ADXL362 provides 12-bit output resolution and has three operating ranges, ±2 g, ±4 g, and ±8 g. It is specified over a minimum temperature range of −40°C to +85°C. For applications
where a noise level less than 480 μg/√Hz is desired, either of its two lower noise modes (down to 120 μg/√Hz) can be selected at a minimal increase in supply current.
The ADP195 is a high-side load switch designed for operation between 1.1 V and 3.6 V and is protected against reverse current flow from output to input. The device contains a low on-resistance, P-channel MOSFET that supports over 1.1 A of continuous load current and minimizes power losses.

(Simplified Schematic: Decoupling and All Connections Not Shown)
Basic Operation of the ADXL362
The ADXL362 is a three-axis, ultralow power acceleration measurement system capable of measuring dynamic acceleration (resulting from motion or shock) as well as static acceleration (that is, gravity).
The moving component of the sensor is a polysilicon, surface micromachined structure, also referred to as a beam, built on top of a silicon wafer. Polysilicon springs suspend the structure over the surface of the wafer and provide a resistance against acceleration forces.
Deflection of the structure is measured using differential capacitors. Each capacitor consists of independent fixed plates and plates attached to the moving mass. Any acceleration deflects the beam and unbalances the differential capacitor, resulting in a sensor output whose amplitude is proportional to acceleration. Phase-sensitive demodulation is used to determine the magnitude and polarity of the acceleration.
Modes of Operation
The three basic modes of operation for the ADXL362 are standby, measurement, and wake-up.
- Placing the ADXL362 in standby mode suspends measurement and reduces current consumption to 10 nA. Any pending data or interrupts are preserved; however, no new information is processed. The ADXL362 powers up in standby mode with all sensor functions turned off.
- Measurement mode is the normal operating mode of the ADXL362. In this mode, acceleration data is continuously read, and the accelerometer consumes less than 3 μA across its entire range of output data rates of up to 400 Hz using a 2.0 V supply. All described features are available while operating in this mode. The ability to continuously output data from the minimum 12.5 Hz to the maximum 400 Hz data rate while still delivering less than 3 μA of current consumption is what defines the ADXL362. as an ultralow power accelerometer. Under sampling and aliasing do not occur with the ADXL362. because it continuously samples the full bandwidth of its sensor at all data rates.
- Wake-up mode is ideal for simple detection of the presence or absence of motion at extremely low power consumption (270 nA at a 2.0 V supply voltage). Wake-up mode is useful particularly for implementation of a motion-activated on/off switch, allowing the rest of the system to be powered down until activity is detected. Wake-up mode reduces current consumption to a very low level by measuring acceleration only 6 times a second to determine whether motion is present. In wake-up mode, all accelerometer features are available with the exception of the activity timer. All registers are accessible, and real-time data is available from the part.
The CN0274 evaluation software uses the wake-up mode of the ADXL362. That is, the ADXL362 is asleep until it detects motion at which point it enters measurement mode.
The ADXL362 offers a few options for decreasing noise at the
expense of only a small increase in current consumption.
The noise performance of the ADXL362 in normal operation, typically 7 LSB rms at 100 Hz bandwidth, is adequate for most applications, depending upon bandwidth and the desired resolution. For cases where lower noise is needed, the ADXL362 provides two lower noise, operating modes that trade reduced noise for somewhat higher supply current.
Table 1. ADXL362 Noise vs. Supply Current
Mode | Noise (µg/√Hz Typical) |
Current Consumption (µA Typical) |
Normal Operation |
380 |
2.7 |
Low Noise |
280 |
4.5 |
Ultralow Noise |
175 |
15 |
Table 1 shows the supply current values and noise densities
obtained for normal operation and the two lower noise modes,
at a typical 3.3 V supply.
The CN0274 evaluation software uses the normal operation noise mode of the ADXL362.
Motion Detection
The ADXL362 has built-in logic that detects activity (acceleration
above a certain threshold) and inactivity (lack of acceleration above a certain threshold).
Detection of an activity or inactivity event is indicated in the status register and can also be configured to generate an interrupt.
In addition, the activity status of the device, that is, whether it is moving or stationary, is indicated by the AWAKE bit.
Activity and inactivity detection can be used when the accelerometer is in either measurement mode or wake-up mode.
Activity Detection
An activity event is detected when acceleration stays above a specified threshold for a user-specified time period. The two activity detection events are absolute and referenced.
- When using absolute activity detection, acceleration samples are compared to a user set threshold to determine whether motion is present. For example, if a threshold of 0.5 g is set, and the acceleration on any axis is 1 g for longer than the user defined activity time, the activity status is asserted. In many applications, it is advantageous for activity detection to be based not on an absolute threshold but on a deviation from a reference point or orientation. This is particularly useful because it removes the effect on activity detection of the static 1 g imposed by gravity. When an accelerometer is stationary, its output can reach 1 g, even when it is not moving. In absolute activity, if the threshold is set to less than 1 g, activity is immediately detected in this case.
- In the referenced activity detection, activity is detected when acceleration samples are at least a user set amount above an internally defined reference, for the user defined amount of time. The reference is calculated when activity detection is engaged, and the first sample obtained is used as a reference point. Activity is only detected when the acceleration has deviated sufficiently from this initial orientation. The referenced configuration results in a very sensitive activity detection that detects even the most subtle motion events.
The CN0274 evaluation software uses the referenced mode of operation when searching for activity.
Inactivity Detection
An inactivity event is detected when acceleration remains below a specified threshold for a specified time. The two inactivity detection events are absolute and referenced.
- In absolute inactivity detection, acceleration samples are compared to a user set threshold for the user set time to determine the absence of motion.
- In referenced inactivity detection, acceleration samples are compared to a user specified reference for a user defined amount of time. When the part first enters the awake state, the first sample is used as a reference point, and the threshold is applied around it. If the acceleration stays inside the threshold, the part enters the asleep state. If an acceleration value moves outside the threshold, this point is then used as a new reference, and the thresholds are reapplied to this new point.
The CN0274 evaluation software uses the referenced mode of operation when searching for inactivity.
Linking Activity and Inactivity Detection
The activity and inactivity detection functions can be used concurrently, and processed manually by a host processor, or they can be configured to interact in several ways:
- In default mode, activity and inactivity detection are both enabled, and all interrupts must be serviced by a host processor; that is, a processor must read each interrupt before it is cleared and can be used again.
- In linked mode, activity and inactivity detection are linked to each other such that only one of the functions is enabled at any given time. Once activity is detected, the device is assumed moving or awake and stops looking for activity: inactivity is expected as the next event so only inactivity detection operates. When inactivity is detected, the device is assumed stationary or asleep. Activity is now expected as the next event so that only activity detection operates. In this mode, a host processor must service each interrupt before the next is enabled.
- In loop mode, motion detection operates as previously described in linked mode; however, interrupts do not need to be serviced by a host processor. This configuration simplifies the implementation of commonly used motion detection and enhances power savings by reducing the amount of power used in bus communication.
- When enabling autosleep mode in linked mode or loop mode, it causes the device to autonomously enter wake-up mode when inactivity is detected, and reenter measurement mode when activity is detected.
The CN0274 evaluation software uses the autosleep and loop modes to demonstrate the functionality of the ADXL362.
The AWAKE Bit
The AWAKE bit is a status bit that indicates whether the ADXL362 is awake or asleep. The device is awake when it has seen an activity condition, and the device is asleep when it has seen an inactivity condition.
The awake signal can be mapped to the INT1 or INT2 pin and can thus be used as a status output to connect or disconnect power to downstream circuitry based on the awake status of the accelerometer. Used in conjunction with loop mode, this configuration implements a trivial, autonomous motion-activated switch.
If the turn-on time of the downstream circuitry can be tolerated, this motion switch configuration can save significant system-level power by eliminating the standby current consumption of the rest of the application. This standby current can often exceed the full operating current of the ADXL362.
Interrupts
Several of the built-in functions of the ADXL362 can trigger interrupts to alert the host processor of certain status conditions.
Interrupts may be mapped to either (or both) of two designated output pins, INT1 and INT2, by setting the appropriate bits in the INTMAP1 and INTMAP2 registers. All functions can be used simultaneously. If multiple interrupts are mapped to one pin, the OR combination of the interrupts determines the status of the pin.
If no functions are mapped to an interrupt pin, that pin is automatically configured to a high impedance (high-Z) state. The pins are placed in this state upon a reset as well.
The INT pins may be connected to the interrupt input of a host processor and interrupts responded to with an interrupt routine. Because multiple functions can be mapped to the same pin, the STATUS register can be used to determine which condition caused the interrupt to trigger.
The CN0274 evaluation software configures the ADXL362 such that when activity is detected, the INT1 pin is high, and when inactivity is detected, the INT1 pin is low.
Test Results
All testing was performed using the EVAL-CN0274-SDPZ and the EVAL-SDP-CS1Z. Functionality of the part is demonstrated by setting the activity threshold at 0.5 g, the inactivity threshold at 0.75 g, and the number of inactivity samples at 20. When looking for activity, only one acceleration sample on any axis is required to cross the threshold.
Starting with the circuit oriented so that the battery pack is flat against the table, the printed circuit board (PCB) can be slowly rotated 90° in any direction causing the acceleration to cross the threshold as it approaches perpendicular to the initial orientation.Figure 2 shows a screen shot of the CN0274 evaluation software showing the ADXL362 first asleep, looking for activity. Then, when Sample 11 crosses the threshold, the ADXL362 enters the awake state and begins looking for inactivity. The thresholds adjust to show the device is now looking for inactivity.

The output of the ADP195, or the interrupt pin itself, was measured using a digital multimeter. When the ADXL362 is awake, the interrupt goes high and drives the EN pin of the ADP195, high, which in turn drives the gate of the MOSFET low, causing the switch to close, connecting any downstream circuitry to the power supply. Conversely, when the ADXL362 is asleep, the interrupt drives the EN pin of the ADP195 low, which in turn drives the gate of the MOSFET high, causing the switch to open.
PCB Layout Considerations
In any circuit where accuracy is crucial, it is important to consider the power supply and ground return layout on the board. The PCB should isolate the digital and analog sections as much as possible. The PCB for this system was constructed in a 4-layer stack up with large area ground plane layers and power plane polygons. See the MT-031 Tutorial for more discussion on layout and grounding, and the MT-101 Tutorial for information on decoupling techniques.
Decouple the power supply to the ADXL362 with 1 μF and 0.1 μF capacitors to properly suppress noise and reduce ripple. Place the capacitors as close to the device as possible. Ceramic capacitors are advised for all high frequency decoupling.
Power supply lines should have as large a trace width as possible to provide low impedance paths and reduce glitch effects on the supply line. Shield clocks and other fast switching digital signals from other parts of the board by digital ground. A photo of the PCB is shown in Figure 3.
A complete design support package for this circuit note can be found at www.analog.com/CN0274-DesignSupport.
Applicable Parts
Applications
Security and Surveillance
- Access Control
- Asset Tracking
CN0247

The circuit shown in Figure 1 is an ultralow, power data acquisition system using the AD7091R 12-bit, 1 MSPS SAR ADC and an AD8031 op amp driver with a total circuit power dissipation of less than 5 mW on a single 3 V supply.
The low power consumption and small package size of the selected components makes this combination an industryleading solution for portable battery-operated systems where power dissipation, cost, and size play a critical role.
The AD7091R requires typically only 350 μA of supply current on the VDD pin at 3 V, which is significantly lower than any competitive ADC offering currently available in the market. This translates to ~1 mW typical power dissipation.
The AD8031 requires only 800 μA of supply current, that results in 2.4 mW typical power dissipation at 3 V supply, making the total power dissipation of the system less than 5 mW when sampling at 1 MSPS with a 10 kHz analog input signal.

Figure 1. 12-Bit, 1 MSPS Low Power ADC with Driver (Simplified Schematic: All Connections Not Shown)
Applicable Parts
Applications
CN0318

Maximum integral nonlinearity (INL) is ±0.5 LSB, and maximum differential nonlinearity (DNL) is ±0.5 LSB for the AD5760 voltage output DAC (B-grade).
The complete system has less than 0.1 LSB peak-to-peak noise and drift measured over a 100 second interval. The circuit is ideal for medical instrumentation, test and measurement, and industrial control applications where precision low drift voltage sources are required.

Figure 1. 16-Bit Accurate, ±10 V Voltage Source (Simplified Schematic: All Connections and Decoupling Not Shown)
Applicable Parts
Applications
CN0158

The ADuM4160 is designed primarily as an isolation element for a peripheral USB device. However, there are occasions when it is useful to isolate a host device. Several issues must be addressed to use the ADuM4160 for this application. Whereas the buffers on the upstream and downstream sides of the ADuM4160 are the same and capable of driving a USB cable, the downstream buffers must be capable of adjusting speed to a full or low speed peripheral that is connected to it.
Unlike the case of building a dedicated peripheral interface where the speed is known and not changed, host applications must adapt. The ADuM4160 is intended to be hardwired to a single speed via pins; therefore, it works when the peripheral plugged into its downstream side is the correct speed, but it fails when the wrong speed peripheral is attached. The best way to address this is to combine the ADuM4160 with a hub controller.
The upstream side of a hub controller can be thought of as a standard fixed speed peripheral port that can be easily isolated with the ADuM4160, whereas the speed of the downstream ports is handled by the hub controller. The hub controller converts peripherals of different speeds to match the upstream port speed. The circuit shown in Figure 1 shows how a two-port hub chip can be used to isolate two downstream host ports in a design that can be made fully compliant with the USB specification.

Figure 1. USB Cable Isolator Circuit
The ADuM4160 provides an inexpensive and easy to implement isolation buffer for medical and industrial peripherals. The challenge that must be met is to use this to create a fully com-pliant host port by pairing the ADuM4160 with a hub chip. As with isolating any peripheral device, the services that the ADuM4160 and hub provide are as follows:
- Directly isolates, in the upstream, the USB D+ and D− lines of a hub chip, allowing the hub to manage the downstream host port activity.
- Implements an automatic scheme for data flow of control that does not require external control lines.
- Provides medical grade isolation.
- Allows creation of one or more host ports that meet the USB-IF certification standards.
- Supports full speed signaling rates.
- Supports flexible power configurations.
The goal of the application circuit is to isolate a hub as if it were a full speed peripheral device. The hub or host function requires that 2.5 W of power be available to each downstream port. Power to run the downstream side of the isolator and power the hub and ports is provided as part of the solution. The application circuit is typical of many medical and industrial applications.
Applicable Parts
Applications
CN0160

- Isolate directly in the USB D+ and D− lines allowing the use of existing USB infrastructure in microprocessors.
- Implement an automatic scheme for data flow of control that does not require external control lines.
- Provide medical grade isolation.
- Allow a complete peripheral to meet the USB-IF certifi-cation standards.
- Support full speed (12 Mbps) and low speed (1.5 Mbps) signaling rates.
- Support flexible power configurations.
The application circuit shown is typical of many medical and industrial applications.

Figure 1. USB Peripheral Isolator Circuit
Applicable Parts
Applications
CN0159

The ADuM4160 is designed primarily as an isolation element for a peripheral USB device. However, there are occasions when it is useful to create an isolated cable function. Several issues must be addressed to use the ADuM4160 for this application. Whereas the buffers on the upstream and downstream sides of the ADuM4160 are the same and capable of driving a USB cable, the downstream buffers must be capable of adjusting speed to a full or low speed peripheral that is connected to it. The upstream connection must act like a peripheral, and the downstream connection must behave like a host.
Unlike the case of building a dedicated peripheral interface where the speed is known and not changed, host applications must adapt to detect whether a low or full speed device has been connected. The ADuM4160 is intended to be hardwired to a single speed via pins; therefore, it works when the peripheral plugged into its downstream side is the correct speed, but it fails when the wrong speed peripheral is attached. The best way to address this is to combine the ADuM4160 with a hub controller.
The upstream side of a hub controller can be thought of as a standard fixed speed peripheral port that can be easily isolated with the ADuM4160, whereas the downstream ports are all handled by the hub controller. However, in many cases, while it is not certifiable as fully USB compliant, a single speed cable is acceptable from a practical standpoint, especially if custom connectors are used so that it cannot be confused with a compliant device. The hub chip can be eliminated, and the design becomes very small and simple.
The ADuM4160 provides an inexpensive and easy way to implement an isolation buffer for medical and industrial peripherals. The challenge that must be met is to use this to create a bus-powered cable isolator by pairing the ADuM4160 with a small isolated dc-to-dc converter such as the ADuM5000. As with isolating any device, the services that the ADuM4160 provides are as follows:
- Directly isolates, in the upstream, the USB D+ and D− lines of a cable.
- Implements an automatic scheme for data flow of control that does not require external control lines.
- Provides medical grade isolation.
- Supports full speed or low speed signaling rates.
- Supports isolated power delivery through the cable.

Figure 1. USB Cable Isolator Circuit
Applicable Parts
Applications
CN0312

The circuit shown in Figure 1 is a dual-channel colorimeter that features a modulated light source transmitter and a synchronous detector receiver. The circuit measures the ratio of light absorbed by the sample and reference containers at three different wavelengths.
The circuit provides an efficient solution for many chemical analysis and environmental monitoring instruments used to measure concentrations and characterize materials through absorption spectroscopy.
The photodiode receiver conditioning path includes a programmable gain transimpedance amplifier for converting the diode current into a voltage and for allowing analysis of different liquids having wide variations in light absorption. The 16-bit sigma delta (Σ-Δ) analog-to-digital converter (ADC) provides additional dynamic range and ensures sufficient resolution for a wide range of photodiode output currents.
Using the modulated source and synchronous detector rather than a constant (dc) source, eliminates measurement errors due to ambient light and low frequency noise and provides higher accuracy.

Applicable Parts
ADG633
CMOS, ±5 V/+5 V/+3 V, Triple SPDT Switch
AD8615
Precision 20 MHz CMOS Single RRIO Operational Amplifier
AD8271
Programmable Gain Precision Difference Amplifier
ADR4525
Ultra-Low-Noise, High-Accuracy 2.5V Voltage Reference
AD8618
Precision 20 MHz CMOS Quad Rail-to-Rail Operational Amplifier
ADG733
CMOS, 2.5 Ω Low Voltage, Triple SPDT Switch
AD7798
3-Channel, Low Noise, Low Power, 16-Bit, Sigma Delta ADC with On-Chip In-Amp
Applications
CN0261

Choosing complementary products for high performance ADCs can be a challenge. The circuit in Figure 1 shows a complete front end solution for the 18-bit, 250 kSPS PulSAR® ADC, which is optimized for ac performance.
The circuit centers on the AD7691, which is a low power ADC (1.35 mW @ 2.5 V and 100 kSPS) from the PulSAR family. The ADC is driven directly from the AD8597 ultralow distortion, ultralow noise amplifier, and the ADC’s reference is the ultralow noise 5 V ADR435. The circuit achieves 101 dB SNR and 118 dB THD with a 1 kHz input tone.

Applicable Parts
Applications
CN0251

The circuit shown in Figure 1 is a flexible signal conditioning circuit for processing signals of wide dynamic range, varying from several mV p-p to 20 V p-p. The circuit provides the necessary conditioning and level shifting and achieves the dynamic range using the internal programmable gain amplifier (PGA) of the high resolution analog-to-digital converter (ADC).
A ±10 V full-scale signal is very typical in process control and industrial automation applications; however, in some situations, the signal can be as small as several mV. Attenuation and level shifting is necessary to process a ±10 V signal with modern low voltage ADCs. However, amplification is needed for small signals to make use of the dynamic range of the ADC. Therefore, a circuit with a programmable gain function is desirable when the input signal varies over a wide range.
In addition, small signals may have large common-mode voltage swings; therefore, high common-mode rejection (CMR) is required. In some applications, where the source impedance is large, high impedance is also necessary for the analog front-end input circuit.

The circuit shown in Figure 1 solves all of these challenges and provides programmable gain, high CMR, and high input impedance. The input signal passes through the 4-channel ADG1409 multiplexer into the AD8226 low cost, wide input range instrumentation amplifier. The AD8226 offers high CMR up to 80 dB and very high input impedance (800 MΩ differential mode and 400 MΩ common mode). A wide input range and rail-to-rail output allow the AD8226 to make full use of the supply rails.
The AD8475 is a fully differential, attenuating amplifier with integrated precision gain resistors. It provides precision attenuation (G = 0.4 or G = 0.8), common-mode level shifting, and single-ended-to-differential conversion. The AD8475 is an easy to use, fully integrated precision gain block, designed to process signal levels up to ±10 V on a single supply. Therefore, the AD8475 is suitable for attenuating signals from the AD8226 up to 20 V p-p, while maintaining high CMR and offering a differential output to drive the differential input ADC.
The AD7192 is a 24-bit sigma-delta (Σ-Δ) ADC with an internal PGA. The on-chip, low noise gain stage (G = 1, 8, 16, 32, 64, or 128) means that signals of large and small amplitude can be interfaced directly to the ADC.
With the combination of the previous parts, the circuit offers very good performance and easy configuration for signals with varying amplitudes. The circuit can be used in industrial automation, process control, instrumentation, and medical equipment applications.
Applicable Parts
ADG1409
4 Ω Ron, 4-Channel ±15 V/+12 V/±5 V iCMOS Multiplexer
AD7192
4.8 kHz Ultra-Low Noise 24-Bit Sigma-Delta ADC with PGA
AD8226
Wide Supply Range, Rail-to-Rail Output Instrumentation Amplifier
AD8475
Precision, Selectable Gain, Fully Differential Funnel Amplifier
ADP1720
50 mA, High Voltage, Micropower Linear Regulator
ADR444
Ultralow Noise, LDO XFET® 4.096V Voltage Reference w/Current Sink and Source
Applications
CN0255

This circuit uses the AD7988-1, a low power (350 μA) PulSAR® analog-to- digital converter (ADC), driven directly from the ADA4841-1 high performance, low voltage, low power op amp. This amplifier was chosen for its excellent dynamic performance and its ability to operate with a single-supply voltage and to provide a rail-to-rail output. In addition, the input commonmode voltage range includes the negative rail.
The AD7988-1 ADC requires an external voltage reference
between 2.4 V and 5.1 V. In this application, the voltage reference
chosen was the ADR4525 precision 2.5 V reference.

Applicable Parts
Applications
CN0277


Figure 1. 18-Bit, 5 MSPS Signal Chain (All Connections and Decoupling Not Shown)
Applicable Parts
AD7960
18-Bit, 5 MSPS PULSAR® Differential ADC
AD8032
2.7 V, 800 µA, 80 MHz Rail-to-Rail I/O Dual Amplifier
AD8031
2.7 V, 800 µA, 80 MHz Rail-to-Rail I/O Single Amplifier
ADA4897-1
1 nV/√Hz, Low Power, Rail-to-Rail Output Amplifiers
ADR4550
Ultra-Low-Noise, High-Accuracy 5.0V Voltage Reference
ADA4897-2
1 nV/√Hz, Low Power Operational Amplifier
Applications
CN0305

This approach is highly useful in portable battery powered or multichannel applications, or where power dissipation is critical. It also provides benefits in applications where the ADC is idle most of the time between conversion bursts.
Drive amplifiers for high performance successive approximation ADCs are typically selected to handle a wide range of input frequencies. However, when an application requires a lower sampling rate, considerable power can be saved because reducing the sampling rate reduces the ADC power dissipation proportionally.
To take full advantage of the power saved by reducing the ADC sampling rate, a low bandwidth, low power amplifier is required.
For example, the 80 MHz ADA4841-1 op amp (12 mW at 10 V) is recommended for inputs up to approximately 100 kHz with the AD7988-5 16-bit successive approximation register (SAR) ADC (3.5 mW at 500 kSPS and 2.1 mW at 300 kSPS). The total system power dissipation including the ADR435 reference (4.65 mW at 7.5 V) is 18.75 mW at 300 kSPS.
For input bandwidths less than 4 kHz and sampling rates less than 300 kSPS, the 1.3 MHz OP1177 op amp (4 mW at 10 V) offers excellent signal-to-noise ratio (SNR) and total harmonic distortion (THD) performance and reduces total system power from 18.75 mW to 10.75 mW, which is a 43% power savings at 300 kSPS.

Applicable Parts
Applications
CN0104

Applicable Parts
ADR435
Ultralow Noise XFET® Voltage References with Current Sink and Source Capability
ADG412
LC2MOS Precision Quad SPST Switch
AD5522
Quad Parametric Measurement Unit With Integrated 16-Bit Level Setting DACs
ADG1209
Low Capacitance, 4-Channel, ±15 V/+12 V iCMOS Multiplexer
AD7685
16-Bit, 250 kSPS PulSAR® ADC in MSOP/QFN
Applications
CN0306

This approach is highly useful in portable battery powered or multichannel applications, or where power dissipation is critical. It also provides benefits in applications where the ADC is idle most of the time between conversion bursts.
Drive amplifiers for high performance successive approximation ADCs are typically selected to handle a wide range of input frequencies. However, when an application requires a lower sampling rate, considerable power can be saved because reducing the sampling rate reduces the ADC power dissipation proportionally.
To take full advantage of the power saved by reducing the ADC sampling rate, a low bandwidth, low power amplifier is required. For instance, the 80 MHz ADA4841-1 op amp (12 mW at 10 V) is recommended for operation with the AD7988-1 16-bit successive approximation register (SAR) ADC (0.7 mW at 100 kSPS). The total system power dissipation including the ADR435 reference (4.65 mW at 7.5 V) is 17.35 mW at 100 kSPS.
For input bandwidths up to 1 kHz and sampling rates of 100 kSPS, the 3 MHz AD8641 op amp (2 mW at 10 V) offers excellent signal-to-noise ratio (SNR) and total harmonic distortion (THD) performance and reduces total system power from 17.35 mW to 7.35 mW, which is a 58% power savings at 100 kSPS.

Applicable Parts
Applications
CN0307

The circuit in Figure 1 is a 16-bit, 6 MSPS, successive approximation (SAR) analog-to-digital converter (ADC) and differential-to-differential driver combination optimized for low noise (signal-to-noise ratio (SNR) = 88.6 dB) and low distortion (total harmonic distortion (THD) = −110 dBc) at low power. The circuit is ideal for high performance multiplexed data acquisition systems, such as portable digital x-ray systems and security scanners, because the SAR architecture can sample without the latency or pipeline delay typically incurred with pipeline ADCs. The 6 MSPS sampling rate allows fast sampling of multiple channels, and the ADC has true 16-bit dc linearity performance and a serial low voltage differential signaling (LVDS) interface for low pin count and low digital noise.

The driver uses two low noise (1 nV/√Hz) ADA4897-1 op amps that maintain the dynamic performance of the AD7625 ADC at low power levels (3 mA per amplifier). The fast settling time (45 ns to 0.1%) of ADA4897-1 makes them ideal for multiplexed applications.
This combination offers industry-leading dynamic performance at low power in a small board area with the AD7625 in a 5 mm × 5 mm, 32-lead LFCSP; the ADA4897-1 in an 8-lead SOIC; and the AD8031 in a 5-lead SOT-23 package.
Applicable Parts
AD8032
2.7 V, 800 µA, 80 MHz Rail-to-Rail I/O Dual Amplifier
AD8031
2.7 V, 800 µA, 80 MHz Rail-to-Rail I/O Single Amplifier
AD7625
16-Bit, 6MSPS PulSAR Differential ADC
ADA4897-1
1 nV/√Hz, Low Power, Rail-to-Rail Output Amplifiers
ADA4897-2
1 nV/√Hz, Low Power Operational Amplifier
ADR434
Low Noise XFET® Voltage References with Current Sink and Source Capability
Applications
Security and Surveillance
- Asset Tracking
- Scanning Equipment
CN0272

Other suitable applications for this circuit are as an analog opto-isolator. It can also be adapted to applications that require larger bandwidth and less resolution such as adaptive speed control systems.
This circuit note discusses the design steps needed to optimize the circuit shown in Figure 1 for a specific bandwidth including stability calculations, noise analysis, and component selection considerations.
Applicable Parts
Applications
CN0105

The AD7626 industry breakthrough dynamic performance of 91.5 dB SNR at 10 MSPS with 16-bit INL performance, no latency, and LVDS interface, all coupled with power dissipation of only 136 mW. A key feature of the SAR architecture used inthe AD7626 is the ability to sample at 10 MSPS without the latency, or "pipeline delay," typically incurred with pipeline ADCs coupled with the excellent linearity performance.
The ADA4932-1 has low distortion (100 dB SFDR @ 10 MHz), fast settling time (9 ns to 0.1%), high bandwidth (560 MHz, −3 dB, G = 1), and low current (9.6 mA). These characteristics make it the ideal choice for driving the AD7626. It also features the functionality to easily set the required output common- mode voltage.
The combination offers industry-leading dynamic performance and small board area with the AD7626 in a 5 mm × 5 mm, 32-lead LFCSP, the ADA4932-1 in a 3 mm × 3 mm, 16-lead LFCSP, and the AD8031 in a 5-lead SOT-23 package.
Applicable Parts
Applications
CN0148

In measurement and protection systems, simultaneous sampling capability is needed to maintain the phase information between the current and voltage channels on multiphase power line networks. The wide dynamic range capability of the AD7606 makes it ideal for capturing both under voltage/current and over voltage/current conditions. The input voltage range is pin-programmable for either ±5 V or ±10 V.
This circuit note describes details of the recommended PC board layout for applications using multiple AD7606 devices. The layout is optimized for channel-to-channel matching and part-to-part matching and will help reduce the complexity of calibration routines in high channel count systems. The circuit provides the ability to use the AD7606 2.5 V internal reference when channel-to-channel matching is important or an external ADR421 precision high accuracy (B grade: ±1 mV max), low drift (B grade: 3 ppm/°C max), low noise (1.75 μV p-p, typical, 0.1 Hz to 10 Hz) reference for high channel applications that require excellent absolute accuracy. The low noise and the stability and accuracy characteristics of the ADR421 make it ideal for high precision conversion applications. The combination of the two devices yields a level of integration, channel density, and accuracy that is unsurpassed in the industry.
Applicable Parts
ADR421
Ultraprecision, Low Noise, 2.500 V XFET® Voltage References
AD7606
8-Channel DAS with 16-Bit, Bipolar, Simultaneous Sampling ADC
AD7606-4
4-Channel DAS with 16-Bit, Bipolar, Simultaneous Sampling ADC
AD7606-6
6-Channel DAS with 16-Bit, Bipolar, Simultaneous Sampling ADC
AD7605-4
4-Channel DAS with 16-Bit, Bipolar Input, Simultaneous Sampling ADC
Applications
CN0385

The circuit can process eight gain-independent channels and is compatible with both single-ended and differential input signals.
The analog front end includes a multiplexer, programmable gain instrumentation amplifier (PGIA); precision analog-to- digital converter (ADC) driver for performing the single-ended to differential conversion; and an 18-bit, 2.0 MSPS precision PulSAR® ADC for sampling the signal on the active channel. Gain configurations of 0.4, 0.8, 1.6, and 3.2 are available.
The maximum sample rate of the system is 2 MSPS in turbo mode, and 1.5 MSPS in normal mode. The channel switching logic is synchronous to the ADC conversions, and the maximum channel switching rate is 1.5 MHz. A single channel can be sampled at up to 2 MSPS with 18-bit resolution in turbo mode. Channel switching rates up to 750 kHz also provide 18-bit performance.

Applicable Parts
AD4003
18-Bit, 2 MSPS, Easy Drive, Differential SAR ADC
AD8251
10 MHz, G = 1, 2, 4, 8 iCMOS® Programmable Gain Instrumentation Amplifier
AD8475
Precision, Selectable Gain, Fully Differential Funnel Amplifier
ADG5207
High Voltage, Latch-Up Proof, 8-Channel Differential Multiplexer
ADR4540
Ultra-Low-Noise, High-Accuracy 4.096V Voltage Reference
ADUM141E
Robust, Quad Channel Isolator W/ Output Enable & 1 Reverse Channel
ADUM3470
Isolated Switching Regulators (4/0 Channel Directionality)
ADP5070
1 A/0.6 A, DC-to-DC Switching Regulator with Independent Positive and Negative Outputs
ADP2441
36 V,1 A, Synchronous, Step-Down DC-DC Regulator
ADP7118
20 V, 200 mA, Low Noise, CMOS LDO Linear Regulator
ADP7182
–28 V, −200 mA, Low Noise, Linear Regulator
Applications
CN0355

The circuit in Figure 1 is a complete, low power signal conditioner for a bridge type sensor and includes a temperature compensation channel. This circuit is ideal for a variety of industrial pressure sensors and load cells that operate with drive voltages of between 5 V and 15 V.
The circuit can process full-scale signals from approximately 10 mV to 1 V, using the internal programmable gain amplifier (PGA) of the 24-bit, sigma-delta (Σ-Δ) ADC, making it suitable for a wide variety of pressure sensors.
The entire circuit uses only three ICs and requires only 1 mA (excluding the bridge current). A ratiometric technique ensures that the accuracy and stability of the system does not depend on a voltage reference.

Applicable Parts
Applications
CN0396


Electrochemical sensors offer several advantages for instruments that detect or measure the concentration of many toxic gases. Most sensors are gas specific and have usable resolutions under one part per million (ppm) of gas concentration.
The Alphasense COH-A2 sensor, which detects carbon monoxide (CO) and hydrogen sulfide (H2S), is used in this example.
The EVAL-CN0396-ARDZ printed circuit board (PCB) is designed in an Arduino-compatible shield form factor and interfaces to the EVAL-ADICUP360 Arduino-compatible platform board for rapid prototyping.
Applicable Parts
AD7798
3-Channel, Low Noise, Low Power, 16-Bit, Sigma Delta ADC with On-Chip In-Amp
ADA4528-1
Precision, Ultralow Noise, RRIO, Zero-Drift Single Op Amp
ADA4528-2
Precision, Ultralow Noise, RRIO, Zero-Drift Dual Op Amp
AD5270
1024-Position, 1% Resistor Tolerance Error, SPI Interface and 50-TP Memory Digital Rheostat
ADT7310
±0.5°C Accurate, 16-Bit Digital SPI Temperature Sensor
ADP7102
20 V, 300 mA, Low Noise, CMOS LDO
ADR3412
Micro-Power, High-Accuracy 1.2V Voltage Reference.
Applications
Building Technology
- Heating Ventilation and Air Conditioning
CN0373

The circuit shown in Figure 1 provides a completely isolated connection between the popular USB bus and an RS-485 or RS-232 bus. Both signal and power isolation ensures a safe USB device interface to an industrial bus or debug port, allowing TIA/EIA-485/232 bus traffic monitoring and the convenience of sending and receiving commands to and from a PC that is not equipped with an RS-485 or RS-232 port.
Isolation in this circuit increases system safety and robustness by providing protection against electrical line surges and breaks the ground connection between bus and digital pins, thereby removing possible ground loops within the system.
The TIA/EIA RS-485 bus standard is one of the most widely used physical layer bus designs in industrial and instrumentation applications. RS-485 offers differential data transmission between multiple systems, often over very long distances. RS-485 communication offers additional robustness through differential communication when compared to the RS-232 standard.
TIA/EIA RS-232 devices are widely used in industrial machines, networking equipment, and scientific instruments. In modern personal computers, which are often used for debugging network problems, USB has displaced RS-232 from most of its peripheral interface roles, and many computers do not come equipped with RS-232 ports. The circuit in Figure 1 offers a robust and compact solution for both RS-232 and RS-485 interfaces.

Applicable Parts
ADM3252E
Isolated, Dual Channel RS-232 Line Driver/Receiver
ADM2587E
2.5 kV Signal and Power Isolated, ±15 kV ESD Protected, Full/Half Duplex RS-485 Transceiver (500kbps)
ADUM3160
Full/Low Speed USB Digital Isolator
ADUM3070
Isolated Switch Regulator With Integrated Feedback
ADP190
Logic Controlled, High-Side Power Switch
ADP7102
20 V, 300 mA, Low Noise, CMOS LDO
Applications
Consumer
CN0363


By using modulated light and digital synchronous detection rather than a constant (dc) source, the system strongly rejects any noise sources at frequencies other than the modulation frequency, providing excellent accuracy.
The dual-channel circuit measures the ratio of light absorbed by the liquids in the sample and reference containers at three different wavelengths. This measurement forms the basis of many chemical analysis and environmental monitoring instruments used to measure concentrations and characterize materials through absorption spectroscopy.
Applicable Parts
AD7175-2
24-Bit, 250 kSPS, Sigma-Delta ADC with 20 µs Settling and True Rail-to-Rail Buffers
ADA4528-1
Precision, Ultralow Noise, RRIO, Zero-Drift Single Op Amp
AD8615
Precision 20 MHz CMOS Single RRIO Operational Amplifier
AD5201
33-Position Digital Potentiometer
ADA4805-1
0.2 µV/°C Offset Drift, 105 MHz Low Power, Low Noise, Rail-to-Rail Amplifier
ADG633
CMOS, ±5 V/+5 V/+3 V, Triple SPDT Switch
ADG733
CMOS, 2.5 Ω Low Voltage, Triple SPDT Switch
ADG704
CMOS, Low Voltage 2.5 Ω 4-Channel Multiplexer
ADG819
0.5 Ω CMOS 1.8 V to 5.5 V 2:1 Mux/SPDT Switch with BBM Switching Action
Applications
CN0370

The circuit in Figure 1 is a complete single-supply, low noise LED current source driver controlled by a 16-bit digital-to-analog converter (DAC). The system maintains ±1 LSB integral and differential nonlinearity and has a 0.1 Hz to 10 Hz noise of less than 45 nA p-p for a full-scale output current of 20 mA.
The innovative output driver amplifier eliminates the crossover nonlinearity normally associated with most rail-to-rail input op amps that can be as high as 4 LSBs or 5 LSBs for a 16-bit system.
This industry-leading solution is ideal for pulse oximetry applications where 1/f noise superimposed on the LED brightness levels affects the overall accuracy of the measurement.
Total power dissipation for the three active devices is less than 20 mW typical when operating on a single 5 V supply.

Figure 1. ±1 LSB Linear 16-Bit LED Current Source Driver (Simplified Schematic: All Connections and Decoupling Not Shown)
Applicable Parts
Applications
CN0359

A carefully selected combination of precision signal conditioning components yields an accuracy of better than 0.3% over a conductivity range of 0.1 μS to 10 S (10 MΩ to 0.1 Ω) with no calibration requirements.
Automatic detection is provided for either 100 Ω or 1000 Ω platinum (Pt) resistance temperature devices (RTDs), allowing the conductivity measurement to be referenced to room temperature.
The system accommodates 2- or 4-wire conductivity cells, and 2-, 3-, or 4-wire RTDs for added accuracy and flexibility.
The circuit generates a precise ac excitation voltage with minimum dc offset to avoid a damaging polarization voltage on the conductivity electrodes. The amplitude and frequency of the ac excitation is user-programmable.
An innovative synchronous sampling technique converts the peak-to-peak amplitude of the excitation voltage and current to a dc value for accuracy and ease in processing using the dual, 24-bit Σ-Δ ADC contained within the precision analog microcontroller.
The intuitive user interface is an LCD display and an encoder push button. The circuit can communicate with a PC using an RS-485 interface if desired, and operates on a single 4 V to 7 V supply.

Applicable Parts
AD8253
10 MHz, G = 1, 10, 100, 1000 iCMOS® Programmable Gain Instrumentation Amplifier
ADA4627-1
36 V, 19 MHz, Low Noise, Low Bias Current, JFET Op Amp
ADA4000-1
Single, Low Cost, Precision JFET Input Operational Amplifier
ADA4638-1
30V Auto-zero, Rail-to-Rail Output Precision Amplifier
ADA4528-2
Precision, Ultralow Noise, RRIO, Zero-Drift Dual Op Amp
ADA4077-2
4 MHz, 7 nV/√Hz, Low Offset and Drift, High Precision Dual Amplifier
AD8542
General-Purpose CMOS Dual Rail-to-Rail Amplifier
ADP2300
1.2 A, 20 V, 700 kHz Nonsynchronous Step-down Switching Regulator
ADP1613
650 kHz /1.3 MHz Step-Up PWM DC-to-DC Switching Converter with 2.0 A Current Limit
ADG1211
Low Capacitance, Low Charge Injection ±15 V/+12 V iCMOS Quad SPST Switches
ADG1419
2.1 Ω On Resistance, ±15 V/+12 V/±5 V, iCMOS SPDT Switch
ADM3483
3.3 V, Low Power, RS-485/RS-422 Transceiver (Half Duplex, 250 kbps, Slew Rate Limited, DE/RE)
ADuCM362
Low Power, Precision Analog Microcontroller with Dual Sigma-Delta ADCs, ARM Cortex-M3
ADuCM363
Low Power, Precision Analog Microcontroller with Single Sigma-Delta ADC, ARM Cortex-M3
Applications
CN0364

The analog input circuit is designed for group isolated industrial analog inputs and can support voltage and current input ranges including ±5 V, ±10 V, 0 V to +5 V, 0 V to +10 V, +4 mA to +20 mA, and 0 mA to +20 mA.
The circuit is powered from a standard 24 V bus supply and generates an isolated 5 V system supply voltage.
Applicable Parts
AD5700-1
Low Power HART Modem with Precision Internal Oscillator
AD7173-8
Low Power, 8-/16-Channel, 31.25 kSPS, 24-Bit, Highly Integrated Sigma-Delta ADC
ADG704
CMOS, Low Voltage 2.5 Ω 4-Channel Multiplexer
ADP2441
36 V,1 A, Synchronous, Step-Down DC-DC Regulator
ADUM3151
3.75 kV, 7-Channel, SPIsolator Digital Isolators for SPI (with 2/1 Aux channel directionality)
ADUM5211
Dual-Channel Isolators with Integrated DC-to-DC Converter (1/1 Channel Directionality)
AD7176-2
24-Bit, 250 kSPS Sigma Delta ADC with 20 µs Settling
AD7173-8
Low Power, 8-/16-Channel, 31.25 kSPS, 24-Bit, Highly Integrated Sigma-Delta ADC
AD7175-2
24-Bit, 250 kSPS, Sigma-Delta ADC with 20 µs Settling and True Rail-to-Rail Buffers
AD7172-2
Low Power, 24-Bit, 31.25 kSPS, Sigma-Delta ADC with True Rail-to-Rail Buffers
AD7177-2
32-Bit, 10 kSPS, Sigma-Delta ADC with 100 µs Settling and True Rail-to-Rail Buffers
AD7172-4
Low Power, with 4- or 8-channel, 24-bit, 31.25 kSPS, Sigma-Delta ADC with True Rail-to-Rail Buffers
Applications
CN0357

Electrochemical sensors offer several advantages for instruments that detect or measure the concentration of many toxic gases. Most sensors are gas specific and have usable resolutions under one part per million (ppm) of gas concentration.
The circuit shown in Figure 1 uses the ADA4528-2, dual auto zero amplifier, which has a maximum offset voltage of 2.5 μV at room temperature and an industry leading 5.6 μV/√Hz of voltage noise density. In addition, the AD5270-20 programmable rheostat is used rather than a fixed transimpedance resistor, allowing for rapid prototyping of different gas sensor systems, without changing the bill of materials.
The ADR3412 precision, low noise, micropower reference establishes the 1.2 V common-mode, pseudo ground reference voltage with 0.1% accuracy and 8 ppm/°C drift.
For applications where measuring fractions of ppm gas concentration is important, using the ADA4528-2 and the ADR3412 makes the circuit performance suitable for interfacing with a 16-bit ADC, such as the AD7790.

Applicable Parts
AD5270
1024-Position, 1% Resistor Tolerance Error, SPI Interface and 50-TP Memory Digital Rheostat
AD7790
16-Bit, Single-Channel, Ultra Low Power, Sigma Delta A/D Converter
AD8500
Micropower Precision CMOS Operational Amplifier
ADA4528-2
Precision, Ultralow Noise, RRIO, Zero-Drift Dual Op Amp
ADR3412
Micro-Power, High-Accuracy 1.2V Voltage Reference.
Applications
Instrumentation & Measurement
CN0348

The circuit in Figure 1 is a complete single-supply,16-bit buffered voltage output DAC that maintains ±1 LSB integral and differential nonlinearity by utilizing a CMOS DAC followed by an innovative amplifier that has no crossover distortion.
The circuit eliminates the crossover nonlinearity associated with most rail-to-rail op amps that can be as high as 4 or 5 LSBs for a 16-bit system.
This industry-leading solution is ideal for industrial process control and instrumentation applications where a compact, single-supply, low cost, and highly linear 16-bit buffered voltage source is required.
Total power dissipation for the three active devices is less than 25 mW typical when operating on a single 6 V supply.

Figure 1. ±1 LSB Linear 16-Bit Buffered Voltage Output DAC (Simplified Schematic, All Connections and Decoupling Not Shown)
Applicable Parts
Applications
CN0314

The circuit shown in Figure 1 is a configurable 4 mA-to-20 mA loop-powered transmitter based on an industry-leading micropower instrumentation amplifier. Total unadjusted error is less than 1%. It can be configured with a single switch as either a transmitter (Figure 1) that converts a differential input voltage into a current output, or as a receiver (Figure 5) that converts a 4 mA-to-20 mA current input to a voltage output.
Figure 1. Robust Loop Powered Configurable Transmitter Circuit with 4 mA-to-20 mA Output
The design is optimized for precision, low noise and low power industrial process control applications. The circuit can accept 0 V to 5V or 0 V to 10 V input range as a transmitter. As a receiver it can provide 0.2 V to 2.3 V or 0.2 V to 4.8 V output range compatible with ADCs using 2.5 V or 5 V references. The supply voltage can range from 12 V to 36 V as a transmitter and 7 V to 36 V as a receiver.
Since the circuit is configurable, a single hardware design can be used as a backup for both transmitter and receiver at the same time, minimizing customer inventory requirements.
Applicable Parts
Applications
Building Technology
- Building Control and Automation
CN0225

The circuit, shown in Figure 1, is a complete analog front end
for digitizing ±10 V industrial level signals with a 16-bit
differential input PulSAR® ADC. The circuit provides a high
impedance instrumentation amplifier input with high CMR,
level shifting, attenuation, and differential conversion, with only
two analog components. Because of the high level of integration,
the circuit saves printed circuit board space and offers a cost
effective solution for a popular industrial application.
Signal levels of up to ±10 V are typical in process control and industrial automation systems. With smaller signal inputs from sensors such as thermocouples and load cells, large commonmode voltage swings are often encountered. This requires a flexible analog input that handles both large and small differential signals with high common-mode rejection and also has a high impedance input.
Figure 1. High Performance Analog Front for Industrial Process Control (Simplified Schematic: All Connections and Decoupling Not Shown)
Attenuation and level shifting are necessary to process
industrial level signals with modern low voltage ADCs. In
addition, fully differential input ADCs offer the advantages of
good common-mode rejection, reduction in second-order
distortion products, and simplified dc trim algorithms.
Industrial signals, therefore, need further conditioning to
properly interface with differential input ADCs.
The circuit in Figure 1 is a complete and highly integrated analog front end industrial level signal conditioner that uses only two active components to drive an AD7687 differential input 16-bit PulSAR ADC: the AD8295 precision in-amp (with two on-chip auxiliary op amps) and the AD8275 level translator/ADC driver. An ADR431 low noise 2.5V XFET® reference supplies the voltage reference for the ADC.
The AD8295 is a precision instrumentation amplifier with two
uncommitted on-chip signal processing amplifiers and two
precisely matched 20 kΩ resistors in a small 4 mm × 4 mm
package.
The AD8275 is a G = 0.2 difference amplifier that can be used to
attenuate ±10 V industrial signals, and the attenuated signal can
be easily interfaced to a single supply low voltage ADC. The
AD8275 performs the attenuation and level shifting function in
the circuit, maintaining good CMR without any need for
external components.
The AD7687 is a 16-bit, successive approximation ADC that operates from a single power supply between 2.3 V and 5.5 V. It has a differential input for good CMR and also offers the ease of use associated with SAR ADCs.
Applicable Parts
Applications
CN0189

The circuit, shown in Figure 1, incorporates a dual axis ADXL203 accelerometer and the AD7887 12-bit successive approximation (SAR) ADC to create a dual axis tilt measurement system.
The ADXL203 is a polysilicon surface micromachined sensor and signal conditioning circuit. Acceleration in the X or Y axis will produce a corresponding output voltage on the XOUT or YOUT output pins of the device. The X axis and Y axis are perpendicular to one another. The AD8608 quad op amp buffers, attenuates, and level shifts the ADXL203 outputs so they are at the proper levels to drive the inputs of the AD7887. The rail-to-rail input/output AD8608 is chosen for its low offset voltage (65 μV maximum), low bias current (1 pA maximum), low noise (8 nV/√Hz), and small footprint (14-lead SOIC or TSSOP).
The AD7887 is configurable for either dual or single channel operation via the on-chip control register. In this application it is configured for dual channel mode, allowing the user to monitor both outputs of the ADXL203, thereby providing a more accurate and complete solution.
The system maintains an accuracy of 1° over 90° and over temperature. The circuit provides this precision, performance, and range in a low cost, low power, small footprint, calibration dependent solution. The ADXL203 is specified over a minimum temperature range of −40°C to +105°C and is available in an 8-terminal ceramic leadless chip carrier package (LCC).

Applicable Parts
Applications
CN0201


A single +5 V supply powers the circuit, and a high efficiency, low ripple boost converter generates the ±15 V that allows processing differential input signals up to ±24.576 V with ±2 LSB INL (maximum), and ±0.5 LSB DNL (typical). For high accuracy applications, this compact and cost-effective circuit offers high precision, as well as low noise.
The successive approximation register (SAR)-based data acquisition system includes true high impedance differential input buffers; therefore, there is no need for additional buffering, as is usually required to reduce kickback in capacitive digital-toanalog converter (DAC)-based SAR analog-to-digital converters (ADCs). In addition, the circuit has high common-mode rejection, eliminating the need for external instrumentation amplifiers, which are typically required in applications where common-mode signals are present.
The ADAS3022 is a complete 16-bit, 1 MSPS data acquisition system that integrates an 8-channel, low leakage multiplexer; a programmable gain instrumentation amplifier stage with a high common-mode rejection; a precision low drift 4.096 V reference; a reference buffer; and a high performance, no latency, 16-bit SAR ADC. The ADAS3022 reduces its power at the end of each conversion cycle; therefore, the operating currents and power scale linearly with throughput make it ideal for the low sampling rates in battery-powered applications.
The ADAS3022 has eight inputs and a COM input that can be configured as eight single-ended channels, eight channels with a common reference, four differential channels, or various combinations of single-ended and differential channels.
In the circuit shown in Figure 1, the reference is supplied by the ADR434 low noise reference buffered by an AD8031 op amp. The AD8031 is ideally suited as a reference buffer because of its ability to drive dynamic loads with fast recovery.
The ADP1613 is a dc-to-dc boost converter with an integrated power switch and provides the ADAS3022 high voltage ±15 V supplies required for the on-chip input multiplexer and the programmable gain instrumentation amplifier without compromising the performance of the ADAS3022.
This circuit offers high precision, as well as low noise, which is ensured by the combination of the ADAS3022, ADP1613, ADR434, and AD8031 precision components.
Applicable Parts
AD8032
2.7 V, 800 µA, 80 MHz Rail-to-Rail I/O Dual Amplifier
AD8031
2.7 V, 800 µA, 80 MHz Rail-to-Rail I/O Single Amplifier
ADP1613
650 kHz /1.3 MHz Step-Up PWM DC-to-DC Switching Converter with 2.0 A Current Limit
ADAS3022
16-Bit, 1 MSPS, 8 Channel Data Acquisition System
ADR434
Low Noise XFET® Voltage References with Current Sink and Source Capability
ADAS3023
16-Bit, 8-Channel Simultaneous Sampling Data Acquisition System
Applications
CN0269

A single channel can be sampled at up to 1.33 MSPS with 18-bit resolution. A channel-to-channel switching rate of 250 kHz between all input channels provides 16-bit performance.
The signal processing circuit combined with a simple 4-bit up-down binary counter provides a simple and cost effective way to realize channel-to-channel switching without an FPGA, CPLD, or high speed processor. The counter can be programmed to count up or count down for sequentially sampling multiple channels, or can be loaded with a fixed binary word for sampling a single channel.
This circuit is an ideal solution for a multichannel data acquisition card for many industrial applications including process control, and power line monitoring.

Figure 1. Multichannel Data Acquisition Circuit (Simplified Schematic: All Components, Connections, and Decoupling Not Shown)
Applicable Parts
AD8065
High Performance, 145 MHz FastFET™ Op Amps
AD8475
Precision, Selectable Gain, Fully Differential Funnel Amplifier
ADG5236
High Voltage Latch-Up Proof, Dual SPDT Switches
ADG5208
High Voltage Latch-Up Proof, 4-/8-Channel Multiplexers
AD7984
18-Bit, 1.33 MSPS PulSAR 10.5 mW ADC in MSOP/QFN
ADR444
Ultralow Noise, LDO XFET® 4.096V Voltage Reference w/Current Sink and Source
Applications
CN0310

This circuit solves the problem of acquiring and digitizing the standard industrial signal levels of ±5 V, ±10 V, and 0 V to 10 V
with precision ADCs having low supply voltages by using an
innovative differential amplifier with internal laser trimmed
resistors to perform the attenuation and level shifting. Applications
for the circuit include process controls (PLC/DCS modules), medical, and scientific multichannel instrumentation and chromatography.

Applicable Parts
Applications
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- AN-385: Wide Temp. Range, Ultralow Drift Accelerometers Using Low Cost Crystal Ovens PDF
- AN-830: Factors Affecting Sensor Response (Rev. 0) PDF
- AN-601: Minimizing Power Consumption of iMEMS® Accelerometers PDF
- AN-378: Reducing the Average Power Consumption of Accelerometers PDF
- AN-282: Fundamentals of Sampled Data Systems PDF
- AN-345: Grounding for Low-and-High-Frequency Circuits PDF
- AN-0991: Active Filter Evaluation Board for Standard SOIC Op Amps (Rev. A) PDF
- AN-1042: ADIS16130 Quick Start Guide and Bias Optimization Tips (Rev. 0) PDF
- AN-1045: iSensor® IMU Mounting Tips (Rev. 0) PDF
- AN-348: Avoiding Passive-Component Pitfalls PDF
- AN-1057: Using an Accelerometer for Inclination Sensing (Rev. 0) PDF
- AN-1049: Calibrating iMEMS® Gyroscopes (Rev. 0) PDF
- AN-1041: iSensor® IMU Quick Start Guide and Bias Optimization Tips (Rev. 0) PDF
- AN-767: Using Absolute Output iMEMS® Gyroscopes with Ratiometric ADCs (Rev. 0) PDF
- AN-688: Phase and Frequency Response of iMEMS® Accelerometers and Gyros (Rev. 0) PDF
- AN-358: Noise and Operational Amplifier Circuits PDF
- AN-1063: Oversampling Technique to Improve ADXL345 Output Resolution (Rev. 0) PDF
- AN-649: Using the Analog Devices Active Filter Design Tool (Rev. 0) PDF
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