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Circuits from the Lab

Circuits from the Lab reference circuits are engineered and tested for quick and easy system integration to help solve today's analog, mixed-signal, and RF design challenges.

March 2014

CN0337: 12-Bit, 300 kSPS, Single-Supply, Fully Isolated RTD Temperature Measurement System with 3-Wire Compensation

This completely isolated 12-bit, 300-kSPS RTD temperature measuring system uses only three active devices to process the output of a Pt100 RTD. An innovative circuit provides lead-wire compensation using a standard 3-wire connection. The circuit operates on a single 3.3-V supply. The total error after room temperature calibration is less than 0.24% FSR for a 10C change in temperature, making it ideal for a wide variety of industrial temperature measurements. Both data and power are isolated, making the circuit robust to high voltages and ground-loop interference often encountered in harsh industrial environments.

CN0335: 12-Bit, 300 kSPS, Single-Supply, Fully Isolated, Data Acquisition System for 10 V Inputs

This completely isolated 12-bit, 300-kSPS data acquisition system uses only three active devices to process 10-V input signals using a single 3.3-V supply. The total error after room temperature calibration is less than 0.1% FSR over a 10C temperature change, making it ideal for a wide variety of industrial measurements. Both data and power are isolated, thereby making the circuit robust to high voltages and ground-loop interference often encountered in harsh industrial environments.

CN0314: Configurable 4-20 mA Loop Powered Transmitter/Receiver using a Micropower Instrumentation Amplifier

This configurable 4 mA-to-20 mA loop-powered transmitter is 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 that converts a differential input voltage into a current output, or as a receiver that converts a 4 mA-to-20 mA current input to a voltage output. 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. The circuit is configurable, so a single hardware design can be used as a backup for both transmitter and receiver at the same time, minimizing inventory requirements.

February 2014

CN0336: 12-Bit, 300 kSPS, Single-Supply, Fully Isolated, Data Acquisition System for 4-20 mA Inputs

This completely isolated 12-bit, 300-kSPS data-acquisition system uses only three active devices to process 4-mA to 20-mA input signals using a single 3.3-V supply. The total error after room temperature calibration is 0.06% FSR over a 10C temperature range, making it ideal for a wide variety of industrial measurements. The small footprint makes it an industry-leading solution for 4-mA to 20-mA data acquisition systems where accuracy, speed, cost, and size play a critical role. Both data and power are isolated, making the circuit robust to high voltages and ground-loop interference often encountered in harsh industrial environments.

January 2014

CN0348: 16-Bit Single-Supply Buffered Voltage Output Digital-to Analog Conversion with Less Than 1 LSB Integral and Differential Nonlinearity

This complete single-supply,16-bit buffered voltage output DAC 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 LSBs to 5 LSBs in a 16-bit system. This industry leading solution is ideal for industrial process control and instrumentation applications that require a compact, single-supply, low-cost, highly linear 16-bit buffered voltage source. Total power dissipation for the three active devices is less than 25 mW typical when operating on a single 6-V supply.

CN0341: Magnetoresistive Linear Position Measurement

This contactless, anisotropic magnetoresistive (AMR) linear position measurement solution features 0.002-inch accuracy over a 0.5-inch range, making it ideal for applications where accurate, high-speed, non-contact length and position measurements are critical. It provides all the signal conditioning, including instrumentation amplifiers, buffers, and a 2-channel ADC, required to efficiently process the low-level AMR sensor bridge outputs. The result is an industry leading position measurement solution suitable for valve and flow measurement, machine tool speed control, motor speed measurement, and other industrial or automotive applications.

CN0332: Magnetoresistive (MR) Rotational Speed Sensor

This low-cost, high-speed, single-supply magnetoresistive (MR) signal conditioner features a minimum PCB footprint. The complete signal conditioning solution amplifies the small output voltage of the magnetoresistive sensor and converts it into a digital output signal with less than 5 ns rise and fall times and approximately 100-ps rms jitter. An excellent alternative to Hall effect sensors, the circuit provides a compact, cost effective, robust solution for high-speed rotational sensing in industrial and automotive applications.

November 2013

CN0340: True RMS RF Detector with 95 dB Detection Range

This true rms responding power detector uses a variable gain amplifier (VGA) and a power detector to provide a 95-dB wide detection range, making it useful for accurate measurement of signals with diverse or varying crest factors, such as those found in GSM/EDGE, CDMA, WCDMA, TD-SCDMA, and LTE receivers and transmitters. The 65-dB detection range of the ADL5902 rms detector is extended to 95 dB by the addition of the AD8368 linear-in-dB VGA.

CN0320: An IQ Demodulator-Based IF-to-Baseband Receiver with IF and Baseband Variable Gain and Programmable Baseband Filtering

This flexible, frequency agile, direct conversion IF-to-baseband receiver features a fixed 5-dB conversion gain to reduce the cascaded noise figure. Variable baseband gain adjusts the signal level, and a programmable low-pass filter eliminates out-of-channel blockers and noise. The filter bandwidth can be dynamically adjusted as the input signal bandwidth changes, ensuring full use of the available dynamic range of the driven ADC. The core circuit is an integrated I/Q demodulator with fractional-N PLL and VCO. With a single variable reference frequency, the PLL/VCO can provide a local oscillator (LO) between 750 MHz and 1150 MHz.

CN0276: High Performance, 10-Bit to 16-Bit Resolver-to-Digital Converter

This complete high-performance resolver-to-digital (RDC) circuit accurately measures angular position and velocity in automotive, avionics, and critical industrial applications where high reliability is required over a wide temperature range. The innovative resolver rotor driver circuit has two modes of operation: high performance and low power. In high-performance mode, the system operates on a 12-V supply and can supply 6.4 V rms (18 V p-p) to the resolver. In low-power mode, the system operates on a 6-V supply and can supply 3.2 V rms (9.2 V p-p) to the resolver, while drawing less than 100 mA. Active filtering is provided in both driver and receiver to minimize the effects of quantization noise. The maximum tracking rate is 3125 rps in 10-bit mode (resolution = 21 arc min) and 156.25 rps in 16-bit mode (resolution = 19.8 arc sec).

CN0269: 18-Bit, 1.33 MSPS, 16-Channel Data Acquisition System

This high-performance multichannel data acquisition circuit has been optimized for fast channel-to-channel switching with industrial signal levels. It can process 16 single-ended channels or eight differential channels, with 18-bit resolution at sampling rates up to 1.33 MSPS. A 250-kHz channel-to-channel switching rate provides 16-bit performance, making it an ideal solution for multichannel data acquisition in process control and power line monitoring applications.

October 2013

CN0323: Magnetoresistive Angle Measurement

This contactless, AMR (anisotropic magnetoresistive) angle measurement solution provides 1 angular accuracy over a 180 range, making it ideal for applications that require accurate, high speed, non-contact angle measurements. The full signal chain, which includes instrumentation amplifiers, buffers, and a dual channel ADC, efficiently processes the AMR sensors low level bridge outputs. The result is an industry leading angle measurement solution suitable for machine tool speed control, crane angle control, motor speed measurement, and other applications.

CN0302: Ultra-Fast Settling PLL with RF to 13 GHz

This PLL circuit uses a 13-GHz fractional-N synthesizer, wideband active loop filter, and VCO, to achieve phase settling time of less than 5 μs to within 5 for a 200-MHz frequency jump. The performance is achieved using an active loop filter with 2.4-MHz bandwidth. This wideband loop filter is enabled by the 110-MHz maximum frequency of the ADF4159s phase-frequency detector (PFD); and the 145-MHz gain-bandwidth product of the AD8065 op amp. The AD8065 can operate on a 24 V supply voltage, allowing control of most wideband VCOs having tuning voltages from 0 V to 18 V.

CN0280: Robust Completely Isolated Current Sense Circuit with Isolated Power Supply for Solar Photovoltaic Converters

This completely isolated current sensor with isolated power source is highly robust and can be mounted close to the sense resistor for accurate measurements and minimum noise pickup. The 16-MHz output data stream from a sigma-delta modulator is processed by a DSP using a SINC3 digital filter. Ideal for monitoring the ac current in solar photovoltaic (PV) converters, the circuit can handle peak ac voltages of several hundred volts and currents between a few mA and 25 A.

September 2013

CN0326: Isolated Low Power pH Monitor with Temperature Compensation

This completely isolated low power pH sensor signal conditioner and digitizer with automatic temperature compensation achieves 0.5% accuracy for pH between 0 and 14, with greater than 14-bits of noise-free code resolution, making it suitable for a variety of industrial applications such as chemical, food processing, water, and wastewater analysis. It supports a wide variety of pH sensors with internal resistance that can range from 1 MΩ to several GΩ. Digital signal and power isolation provides immunity to noise and transient voltages often encountered in harsh industrial environments.

CN0277: High-Precision, 18-Bit, 5 MSPS, Low Power Data Acquisition Signal-Chain

This 18-bit, 5-MSPS, low-power, low-noise, high-precision, complete data-acquisition signal-chain solution dissipates only 122 mW. The reference, reference buffer, driver amplifiers, and ADC provide an optimized solution with industry-leading 99-dB SNR and −117-dB THD. Its low power and small PCB footprint make it ideal for portable applications.

August 2013

CN0290: Extending the Low-Frequency Range of a High-Performance Phase Locked Loop

This high-performance phase locked loop (PLL) uses high-speed clock buffers and low-noise LDOs to maintain low phase noise even at low reference and RF frequencies. For example, the ADF4106 PLL specifies a 20-MHz minimum reference frequency and a 500-MHz minimum RF input frequency. This frequency range can be lowered to a 10-MHz reference frequency and a 100-MHz RF input frequency using additional clock buffers.

CN0287: Isolated 4-Channel Thermocouple/RTD Temperature Measurement System with 0.5C Accuracy

This completely isolated 4-channel temperature measurement circuit, optimized for performance, input flexibility, robustness, and low cost, supports all types of thermocouples with cold-junction compensation and 2-, 3-, or 4-wire RTDs with resistances up to 4 kΩ. The RTD excitation current is programmable for optimum noise and linearity. RTD measurements achieve 0.1C typical accuracy, and Type-K thermocouple measurements achieve 0.05C typical accuracy. The circuit uses a 4-channel AD7193 24-bit sigma-delta ADC with on-chip PGA for high accuracy and low noise. Input transient and overvoltage protection are provided by low-leakage transient voltage suppressors and Schottky diodes. The SPI-compatible digital inputs and outputs are isolated to 2500 V rms, and the circuit operates on a fully isolated power supply.

CN0239: Broadband 6 GHz Active Mixer with a Glueless Local Oscillator Interface

This 10-MHz to 6-GHz wideband active mixer has a direct interface to a frequency synthesizer-based low phase noise local oscillator (LO). It offers an optimum solution for wideband applications that require frequency conversion to higher or lower frequencies. The two-chip circuit covers a broad LO frequency range from 35 MHz to 4400 MHz. The LO interface is simple and glueless, eliminating the need for a balun, matching network, and LO buffer. In addition, the mixer bias adjust function allows optimization of IP3, noise figure, and supply current based on the application requirements or on the size of the input signal.

July 2013

CN0303: MEMS-Based Vibration Analyzer with Frequency Response Compensation

This circuit offers a high linearity, low noise, wide-bandwidth vibration sensing solution that is ideal for applications, such as bearing analysis, engine monitoring, and shock detection, that require high dynamic range (70 g to 500 g) and flat frequency response to 22 kHz.

CN0284: High-Performance, Low-Noise Studio Microphone with MEMS Microphones, Analog Beamforming, and Power Management

This professional-grade studio or live-performance microphone uses up to 32 analog MEMS microphones connected to op amps and a difference amplifier. Designed for low noise, its output is linear for acoustic inputs up to 131 dB SPL. Powered from a single 9-V battery, the 9-V and 1.8-V power rails are generated from two voltage regulators. The ADMP411, which consists of a MEMS microphone element and an impedance-matching amplifier, has a frequency response that is flat to 28 Hz, making it ideal for full-bandwidth, wide dynamic range audio capture.

May 2013

CN0325: PLC/DCS Universal Analog Input Using Either 4 or 6 Pin Terminal Block

This circuit provides two, 16-bit, fully isolated, universal analog input channels suitable for programmable logic controller (PLC) and distributed control system (DCS) modules. Both channels are software programmable and support a number of voltage and current ranges and thermocouple and RTD types. The inputs are protected for dc overvoltage conditions of 30 V. The demonstration board contains two fully isolated universal input channels: in one, the voltage, current, thermocouple, and RTD inputs all share the same terminals to minimize the number of pins required; in the other, separate terminals for voltage/current inputs and thermocouple/RTD inputs provides a lower part count and component cost.

CN0319: 4 mA-to-20 mA, Loop Powered Temperature Monitor Using the Integrated PWM on the ADuCM360 Precision Analog Microcontroller

This circuit provides a low cost solution to temperature monitoring because most of the circuit functionality is integrated into the ADuCM360 precision analog microcontroller, including dual 24-bit Σ-Δ ADCs, the ARM Cortex-M3 processor core, and the PWM/DAC features for controlling the 4 mA-to-20 mA loop for loop voltages up to 28 V.

CN0318: 16-Bit, Linear, Ultra Stable, Low Noise, Bipolar 10 V DC Voltage Source

This 16-bit, ultra-stable, low-noise, precision, bipolar (10 V) voltage source requires a minimum number of precision external components. It features 0.5 LSB maximum integral nonlinearity (INL) and differential nonlinearity (DNL) with the AD5760 voltage-output DAC (B-grade). The complete system has less than 0.1-LSB p-p 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.

CN0301: Universal LVDT Signal Conditioning Circuit

This complete adjustment-free linear variable differential transformer (LVDT) signal conditioning 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 AD698 LVDT signal conditioner, which 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 82-dB dynamic range and 250-Hz system bandwidth, making it ideal for precision industrial position and gauging applications.

CN0300: Complete Closed-Loop Precision Analog Microcontroller Thermocouple Measurement System with 4 mA to 20 mA Output

This circuit uses the ADuCM360 precision analog microcontroller in an accurate thermocouple temperature monitoring application and controls the 4-mA to 20-mA output current. The ADuCM360 integrates two 24-bit sigma-delta (Σ-Δ) analog-to-digital converters (ADCs), two programmable current sources, a 12-bit digital-to-analog converter (DAC), and a 1.2 V internal reference, as well as an ARM Cortex-M3 core, 126 kB flash, 8 kB SRAM, and various digital peripherals, such as UART, timers, SPIs, and I2C interfaces. The ADuCM360 is connected to a type-T thermocouple and a 100-Ω platinum resistance temperature detector, which is used for cold junction compensation. The low power Cortex-M3 core converts the ADC readings to a real temperature value. The −200C to +350C type-T temperature range is converted to a 4-mA to 20-mA output current. The loop-powered circuit provides a complete solution for thermocouple measurements with a minimum requirement for external components.

CN0296: Low Cost, High Performance Sound Bar System

This low-cost, high-performance sound bar system can accept an analog stereo audio signal as an input and output up to eight channels of audio with discrete processing on each channel. The circuit offers low power consumption and high efficiency without sacrificing audio quality, making it ideal for small docking stations and portable media devices. The circuit is capable of driving headphones without the need of additional components. The ADAU1761 low power, stereo audio codec with integrated SigmaDSP digital audio processing accepts two audio channels. It is optimized for audio applications and programmed using SigmaStudio development software for ease of use and faster development. The output of the ADAU1761 can send up to eight channels of digital audio data to the output amplifiers using the serial interface. The ADAU1761 allows different audio signal processing in each channel, such as volume control, custom equalization, filtering, and spatialization effects tuned to the specific speaker configuration. The ADAU1761 processes and converts analog audio to digital format and drives the SSM2518 power amplifier. The SSM2518 is a digital input class-D audio power amplifier that can output two channels of audio with a continuous power of 2 watts each into a 4 Ω load. The channel-mapping feature of the SSM2518 allows it to select the specific channel to output among those that are available in the interface, making it ideal for surround sound applications.

CN0295: Flexible, 4 mA-to-20 mA Pressure Sensor Transmitter with Voltage or Current Drive

This flexible current transmitter converts the differential voltage output from a pressure sensor to a 4-mA to 20-mA current. Optimized for a wide variety of bridge-based voltage or current driven pressure sensors, it utilizes only five active devices and has a total unadjusted error of less than 1%. The power supply voltage can range from 7 V to 36 V depending on the component and sensor driver configuration. The input of the circuit is protected for ESD and voltages beyond the supply rail, making it ideal for industrial applications.

CN0289: Flexible, 4 mA-to-20 mA, Loop-Powered Pressure Sensor Transmitter with Voltage or Current Drive

This robust, flexible loop-powered current transmitter converts the differential voltage output from a pressure sensor to a 4 mA-to-20 mA current output. Optimized for a wide variety of bridge based voltage or current driven pressure sensors, the design uses only four active devices and has a total unadjusted error of less than 1%. The loop supply voltage can range from 12 V to 36 V. The input of the circuit is protected for ESD and voltages beyond the supply rail, making it ideal for industrial applications.

CN0249: 14-Bit, 125 MSPS Quad ADC with SNR Enhanced by Post Digital Summation

This quad 14-bit, 125-MSPS ADC system uses post digital summation to increase the signal-to-noise ratio (SNR) from 74 dBFS for a single ADC to 78.5 dBFS for the quad ADC with summation. Especially suitable for applications such as ultrasound and radar that require high SNR, this technique makes use of modern high-performance low-power quad pipelined ADCs. The circuit makes use of the fundamental principle that uncorrelated noise sources add on a root-sum-square (rss) basis, while signal voltages add on a linear basis.

April 2013

CN0321: Fully Isolated, Single Channel Voltage and 4 mA to 20 mA Output with HART

This complete, fully isolated, analog output channel is suitable for programmable logic controllers (PLCs) and distributed control system (DCS) modules that require standard 4 mA to 20 mA HART-compatible current outputs and unipolar or bipolar output voltage ranges. It provides a flexible building block for channel-to-channel isolated PLC/DCS output modules or any other industrial application that requires a fully isolated analog output. The circuit also includes external protection on the analog output terminals. The AD5422 16-bit digital-to-analog converter (DAC) is software configurable and provides all the necessary current and voltage outputs. The AD5700-1 HART-compliant modem, used in conjunction with the AD5422, forms a complete HART-compatible 4 mA to 20 mA solution. The AD5700-1 includes a precision internal oscillator that provides additional space savings, especially in channel-to-channel isolated applications.


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