Data Acquisition

The AD7768-1 is a low power, high performance, Σ-Δ analog-to-digital converter (ADC), with a Σ-Δ modulator and digital filter for precision conversion of both ac and dc signals. The AD7768-1 is a single-channel version of the AD7768, an 8-channel, simultaneously sampling, Σ-Δ ADC. The AD7768-1 provides a single configurable and reusable data acquisition (DAQ) footprint, which establishes a new industry standard in combined ac and dc performance and enables instrumentation and industrial system designers to design across multiple measurement variants for both isolated and nonisolated applications.

The AD7768-1 achieves a 108.5 dB dynamic range when using the low ripple, finite impulse response (FIR) digital filter at 256 kSPS, giving 110.8 kHz input bandwidth, combined with ±1.1 ppm integral nonlinearity (INL), ±30 µV offset error, and ±30 ppm gain error.

A wider bandwidth, up to 500 kHz Nyquist (filter −3 dB point of 204 kHz), is available using the sinc5 filter, enabling a view of signals over an extended range.

The AD7768-1 offers the user the flexibility to configure and optimize for input bandwidth vs. output data rate (ODR) and vs. power dissipation. The flexibility of the AD7768-1 allows dynamic analysis of a changing input signal, making the device particularly useful in general-purpose DAQ systems. The selection of one of three available power modes allows the designer to achieve required noise targets while minimizing power consumption. The design of the AD7768-1 is unique in that it becomes a reusable and flexible platform for low power dc and high performance ac measurement modules.

The AD7768-1 achieves the optimum balance of dc and ac performance with excellent power efficiency. The following three operating modes allow the user to trade off the input bandwidth vs. power budgets:

• Fast mode offers both a sinc filter with up to 256 kSPS and 52.2 kHz of bandwidth, and 26.4 mW of power consumption, or a FIR filter with up to 256 kSPS, 110.8 kHz of bandwidth and 36.8 mW of power consumption.
• Median mode offers a FIR filter with up to 128 kSPS, 55.4 kHz of bandwidth and 19.7 mW of power consumption.
• Low power mode offers a FIR filter with up to 32 kSPS, 13.85 kHz of bandwidth and 6.75 mW of power consumption.

The AD7768-1 offers extensive digital filtering capabilities that meet a wide range of system requirements. The filter options allow configuration for frequency domain measurements with tight gain error over frequency, linear phase response requirements (brick wall filter), a low latency path (sinc5 or sinc3) for use in control loop applications, and measuring dc inputs with the ability to configure the sinc3 filter to reject the line frequency of either 50 Hz or 60 Hz. All filters offer programmable decimation.

A 1.024 MHz sinc5 filter path exists for users seeking an even higher ODR than is achievable using the low ripple FIR filter. This path is quantization noise limited. Therefore, it is best suited for customers requiring minimum latency for control loops or implementing custom digital filtering on an external field programmable gate array (FPGA) or digital signal processor (DSP).

The filter options include the following:

• A low ripple FIR filter with a ±0.005 dB pass-band ripple to 102.4 kHz.
• A low latency sinc5 filter with up to a 1.024 MHz data rate to maximize control loop responsiveness.
• A low latency sinc3 filter that is fully programmable, with 50 Hz/60 Hz rejection capabilities.

When using the AD7768-1, embedded analog functionality within the AD7768-1 greatly reduces the design burden over the entire application range. The precharge buffer on each analog input decreases the analog input current compared to competing products, simplifying the task of an external amplifier to drive the analog input.

A full buffer input on the reference reduces the input current, providing a high impedance input for the external reference device or in buffering any reference sense resistor scenarios used in ratiometric measurements.

The device operates with a 5.0 V AVDD1 − AVSS supply, a 2.0 V to 5.0 V AVDD2 − AVSS supply, and a 1.8 V to 3.3 V IOVDD − DGND supply.

In low power mode, the AVDD1, AVDD2, and IOVDD supplies can run from a single 3.0 V rail.

The device requires an external reference. The absolute input reference (REF_IN) voltage range is 1 V to AVDD1 − AVSS.

The specified operating temperature range is −40°C to +125°C. The device is housed in a 4 mm × 5 mm, 28-lead LFCSP.

Note that, throughout this data sheet, multifunction pins, such as XTAL2/MCLK, are referred to either by the entire pin name or by a single function of the pin, for example, MCLK, when only that function is relevant.

Applications

• Platform ADC to serve a superset of measurements and sensor types
  • Sound and vibration, acoustic, and material science research and development
  • Control and hardware in loop verification
  • Condition monitoring for predictive maintenance
  • Electrical test and measurement
  • Audio testing and current and voltage measurement
  • Clinical electroencephalogram (EEG), electromyogram (EMG), and electrocardiogram (ECG) vital signs monitoring
  • USB-, PXI-, and Ethernet-based modular DAQ
  • Channel to channel isolated modular DAQ designs

The AD4003/AD4007/AD4011 are high accuracy, high speed, low power, 18-bit, Easy Drive, precision successive approximation register (SAR) analog-to-digital converters (ADCs). The high throughput allows both accurate capture of high frequency signals and decimation to achieve higher SNR, while also reducing antialiasing filter challenges.

Easy Drive features reduce signal chain complexity and power consumption, and enable higher channel density. The reduced input current, particularly in high-Z mode, coupled with a long signal acquisition phase, eliminates the need for a dedicated high power, high speed ADC driver, which broadens the range of low power precision amplifiers that can drive these ADCs directly (see Figure 2). The input span compression feature enables the ADC driver amplifier and the ADC to operate off common supply rails without the need for a negative supply while preserving the full ADC code range. The input overvoltage clamp protects the ADC inputs against overvoltages, minimizes disturbance on the reference pin, and eliminates the need for external protection diodes.

The low serial peripheral interface (SPI) clock rate (75 MHz for the AD4003 in turbo mode) reduces the digital input/output power consumption, broadens processor options, and simplifies the task of sending data across digital isolation.

The SPI-compatible versatile serial interface features seven different programmable modes with an optional busy indicator. Using the SDI input, several ADCs can be daisy-chained on a single 3-wire bus. The AD4003/AD4007/AD4011 are compatible with 1.8 V, 2.5 V, 3 V, and 5 V logic, using the separate supply, VIO.

Applications

• Automatic test equipment
• Machine automation
• Medical equipment
• Battery-powered equipment
• Precision data acquisition systems

The ADR4520/ADR4525/ADR4530/ADR4533/ADR4540/ADR4550 devices are high precision, low power, low noise voltage references featuring ±0.02% maximum initial error, excellent temperature stability, and low output noise.

This family of voltage references uses an innovative core topology to achieve high accuracy while offering industry-leading temperature stability and noise performance. The low, thermally induced output voltage hysteresis and low long-term output voltage drift of the devices also improve system accuracy over time and temperature variations.

A maximum operating current of 950 μA and a maximum low dropout voltage of 300 mV allow the devices to function very well in portable equipment.

The ADR4520/ADR4525/ADR4530/ADR4533/ADR4540/ADR4550 series of references are each provided in an 8-lead SOIC package and are available in a wide range of output voltages, all of which are specified over the extended industrial temperature range of −40°C to +125°C. The ADR4525W, available in an 8-lead SOIC package, is qualified for automotive applications.

Applications

• Precision data acquisition systems
• High-resolution data converters
• High-precision measurement devices
• Industrial instrumentation
• Medical devices
• Automotive battery monitoring

The AD5791 is a single 20-bit, unbuffered voltage-output DAC that operates from a bipolar supply of up to 33 V. The AD5791 accepts a positive reference input in the range 5 V to VDD – 2.5V and a negative reference input in the range VSS + 2.5 V to 0 V. The AD5791 offers a relative accuracy specification of ±1 LSB max, and operation is guaranteed monotonic with a ±1 LSB DNL max specification.

The part uses a versatile 3-wire serial interface that operates at clock rates up to 35 MHz and that is compatible with standard SPI, QSPI™, MICROWIRE™, and DSP interface standards. The part incorporates a power-on reset circuit that ensures the DAC output powers up to 0 V and in a known output impedance state and remains in this state until a valid write to the device takes place. The part provides an output clamp feature that places the output in a defined load state.

Product Highlights

1. 1 ppm Accuracy.
2. Wide Power Supply Range up to ±16.5 V.
3. Operating Temperature Range: −40°C to +125°C.
4. Low 7.5 nV/√Hz Noise Spectral Density.
5. Low 0.05 ppm/°C Temperature Drift.

The AD5686R nanoDAC+™ is a quad, 16-bit, rail-to-rail, voltage output DAC. The device includes a 2.5V, 2ppm/˚C internal reference (enabled by default) and a gain select pin giving a full-scale output of 2.5V (gain=1) or 5V (gain=2).

The device operates from a single 2.7 V to 5.5 V supply, is guaranteed monotonic by design and exhibits less than 0.1% FSR gain error and 1.5mV offset error performance. The device is available in a 3mm X 3mm LFCSP and a TSSOP package.

The AD5686R also incorporates a power-on-reset circuit and a RSTSEL pin that ensures the DAC outputs power up to zero-scale or midscale, and remain there until a valid write takes place. Each device contains a per-channel power-down feature that reduces the current consumption of the device to 4 uA at 3 V while in power-down mode.

The AD5686R employs a versatile SPI interface that operates at clock rates up to 50 MHz and includes a V_LOGIC pin intended for 1.8V/3V/5V logic.

Product Highlights

1. High Relative Accuracy: AD5686R (16-bit): ±2LSB INL max
2. Low drift on-chip reference: 2.5 V, 2 ppm/°C temperature drift.
3. Two package options: 3mm × 3mm 16 lead LFCSP or 16 lead TSSOP

Applications

• Optical transceivers
• Base-station power amplifiers
• Process control (PLC I/O cards)
• Industrial automation
• Data acquisition systems

The ADA4807-1/ADA4807-2 are low power, low noise, rail-to-rail voltage feedback amplifiers with exceptionally high performance. They are designed to have the lowest input noise (3.1 nV/√Hz and 0.7 pA/√Hz) among high speed, rail-to-rail amplifiers in the industry while operating on only 1 mA or less of quiescent supply current, making them ideal for a wide range of applications from battery-powered, portable instrumentation to high speed systems where component density requires lower power dissipation. The ADA4807 operate over a wide range of supply voltages from ±1.5 V to ±5 V, as well as from 3 V to 10 V single supplies, and include a disable feature that allows reduction of the typical quiescent supply current to 2.4 μA or less when asserted.

For systems with high dynamic range signals, the output voltage swings to within 50 mV of each rail, maximizing the output cdynamic range, and the full, rail-to-rail input stage permits input operation up to and beyond the supply rails.

The ADA4807 feature high speed performance of 180 MHz small signal −3 dB bandwidth, a 225 V/μs slew rate, and a settling time of 47 ns to 0.1% (4 V step) with a low input offset voltage of ±20 μV and 0.7 μV/°C drift. For ±5 V supplies, the HD2 is −112 dBc and HD3 is –115 dBc for a 2 V p-p, 100 kHz output signal driving a 1 kΩ load. The low distortion and fast settling time make these amplifiers ideal for driving high speed single-supply precision ADCs with up to 18-bit resolution. The ADA4807 deliver this excellent performance while consuming 1 mA or less of quiescent current.

The ADA4807-1 (single) is available in space-saving 6-lead SC70 and 6-lead SOT-23 packages. The ADA4807-2 (dual) is available in 10-lead LFCSP and 8-lead MSOP packages. The ADA4807 operate over the −40°C to +125°C industrial temperature range.

• High speed, battery operated systems
• High component density systems
• High resolution analog-to-digital converter (ADC) drivers
• Portable test instruments
• Active filters

The ADA4610-1/ADA4610-2/ADA4610-4 are precision junction field effect transistor (JFET) amplifiers that feature low input noise voltage, current noise, offset voltage, input bias current, and rail-to-rail output. The ADA4610-1 is a single amplifier, the ADA4610-2 is a dual amplifier, and the ADA4610-4 is a quad amplifier.

The combination of low offset, noise, and very low input bias current makes these amplifiers especially suitable for high impedance sensor amplification and precise current measurements using shunts. With excellent dc precision, low noise, and fast settling time, the ADA4610-1/ADA4610-2/ADA4610-4 provide superior accuracy in medical instruments, electronic measurement, and automated test equipment. Unlike many competitive amplifiers, the ADA4610-1/ADA4610-2/ADA4610-4 maintain fast settling performance with substantial capacitive loads. Unlike many older JFET amplifiers, the ADA4610-1/ADA4610-2/ADA4610-4 do not suffer from output phase reversal when input voltages exceed the maximum common-mode voltage range.

The fast slew rate and great stability with capacitive loads make the ADA4610-1/ADA4610-2/ADA4610-4 ideal for high performance filters. Low input bias currents, low offset, and low noise result in a wide dynamic range for photodiode amplifier circuits. Low noise and distortion, high output current, and excellent speed make the ADA4610-1/ADA4610-2/ ADA4610-4 great choices for audio applications.

The ADA4610-1/ADA4610-2/ADA4610-4 are specified over the −40°C to +125°C extended industrial temperature range.

The ADA4610-1 is available in an 8-lead SOIC package and in a 5-lead SOT-23 package. The ADA4610-2 is available in 8-lead SOIC, 8-lead MSOP, and 8-lead LFCSP packages. The ADA4610-4 is available in a 14-lead SOIC package and in a 16-lead LFCSP.

Applications

• Instrumentation
• Medical instruments
• Multipole filters
• Precision current measurement
• Photodiode amplifiers
• Sensors
• Audio

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)

The circuit shown in Figure 1 is a flexible, 4-channel, low power thermocouple measurement circuit with an overall power consumption of less than 8 mW. The circuit has a multiplexed front end, followed by an instrumentation amplifier that performs cold junction compensation (0°C to 50°C) and converts the thermocouple output to a voltage with a precise scale factor of 5 mV/°C. The error is less than 2°C, over a measurement range of −25°C to +400°C, and is primarily due to the thermocouple nonlinearity. A nonlinearity correction algorithim reduces the error to less than 0.5°C over a 900°C measurement range. Noise free resolution is less than 0.1°C.

The signal is then digitized by a 24-bit Σ-Δ ADC, and the digital value is provided on an SPI serial interface. With the PMOD form factor for rapid prototyping, the design requires minimal PC board area and is ideal for applications that require precise thermocouple temperature measurements.

The AD8675 precision op amp has low offset voltage (75 μV maximum), low noise (2.8 nV/√Hz typical), and is an optimum output buffer for the AD5780. The AD5780 has two internal matched feedforward and feedback resistors, which are connected to the AD8675 op amp and provide the 10 V offset voltage. This allows an output voltage swing of ±10 V with a single external 10 V reference.

The digital input to the circuit is serial and is compatible with standard SPI, QSPI, MICROWIRE^®, and DSP interface standards. For high accuracy applications, the compact circuit offers high precision, as well as low noise—this is ensured by the combination of the AD5780, ADR445, and AD8675 precision components.

This combination of parts provides industry-leading 18-bit integral nonlinearity (INL) of ±1 LSB and differential nonlinearity (DNL) of ±0.75 LSB, with guaranteed monotonicity, as well as low power, small PCB area, and cost effectiveness in an LFCSP package.

Figure 1. 18-Bit Accurate, ±10V Voltage Source (Simplified Schematic: All Connections and Decoupling Not Shown)

The circuit shown in Figure 1 provides a programmable 20-bit voltage with an output range −10 V to +10 V, ±1 LSB integral nonlinearity, ±1 LSB differential nonlinearity, and low noise.

The digital input to the circuit is serial and is compatible with standard SPI, QSPI™, MICROWIRE^®, and DSP interface standards. For high accuracy applications, the circuit offers high precision, as well as low noise, and this is ensured by the combination of the AD5791, AD8675, and AD8676 precision components.

The reference buffer is critical to the design because the input impedance at the DAC reference input is heavily code dependent and will lead to linearity errors if the DAC reference is not adequately buffered. With a high open-loop gain of 120 dB, the AD8676 has been proven and tested to meet the settling time, offset voltage, and low impedance drive capability required by this circuit application. The AD5791 is characte-rized and factory calibrated using the AD8676 dual op amp to buffer its voltage reference inputs, further enhancing confidence in partnering the components.

This combination of parts provides industry-leading 20-bit integral nonlinearity (INL) of ±1 LSB and differential nonlinearity (DNL) of ±1 LSB, with guaranteed monotonicity, as well as low power, small PCB area, and cost effectiveness.

Figure 1. 20-Bit Accurate, ±10 V Voltage Source (Simplified Schematic: All Connections and Decoupling Not Shown)

The circuit in Figure 1 is a two-channel, bank isolated, wide bandwidth data acquisition (DAQ) system, implemented with a simultaneous sampling architecture using an analog-to-digital converter (ADC) per channel. The system achieves high channel density along with isolation between the bank and the digital backplane, all while delivering exceptional performance. The design also makes efficient use of isolation channels by configuring the ADCs in daisy-chain mode and utilizing an isolator product with a trimmed delay clock feature. Power generation is also simplified using an isolator with an integrated pulse width modulation (PWM) controller and transformer driver to perform dc-to-dc conversion across the isolation barrier. The system also includes many common features of a typical DAQ signal chain, including input circuit protection, programmable gain channels, high accuracy, and high performance.

The simultaneous sampling realizes multiple channels without sample rate limitations inherent in multiplexed DAQ signal chains. The analog front end (AFE) design is also simpler than the multiplexed option, because the settling performance requirements of the system are less demanding. Sampling occurs simultaneously for each channel, while sequential sampling systems have delays between channels.

Digital bank isolated DAQ designs provide protection for digital back end circuitry and reduce ground loop and common-mode interference between banks. They feature multiple DAQ signal chains per ground plane, and can be implemented with fewer digital isolation devices than channel-to-channel isolated systems.

The Analog Devices, Inc., ADA4945-1CP-EBZ evaluation board allows the user to evaluate the performance of the ADA4945-1 fully differential amplifier. The ADA4945-1CP-EBZ evaluation board can be configured to accept either a single-ended or differential input signal.

The ADA4945-1CP-EBZ evaluation board uses several 2-pin and 3-pin headers to control various features of the ADA4945-1. Apply the proper jumpers to set the ADA4945-1 high and low output clamp levels, set the ADA4945-1 output common-mode voltage, choose high or low power mode for the ADA4945-1, and set the ADA4945-1 digital ground level.

Optimized power and ground planes ensure low noise and high speed operation. Component placement and power supply bypassing provide maximum circuit flexibility and performance. The ADA4945-1CP-EBZ evaluation board accepts 0402 surface mount technology (SMT) components, 0805 bypass capacitors, and 2.54 mm headers.

Input and output signals are brought to and from the board via 50 Ω, side launch Subminiature Version A (SMA) connectors.

Full specifications on the ADA4945-1 are available in the ADA4945-1 data sheet. Consult the data sheet in conjunction with this user guide when working with the ADA4945-1CP-EBZ evaluation board.