Avionics

The test system shown in Figure 1 is an accurate, cost effective, 8-channel battery testing system for single-cell, lithium ion (Li-ion) batteries with open circuit voltage (OCV) between 3.5 V and 4.4 V.

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.

The circuit shown in Figure 1 is a highly integrated 16-bit, 1 MSPS, multiplexed 8-channel flexible data acquisition system (DAS) with a programmable gain instrumentation amplifier (PGIA) capable of handling the full range of industrial signal levels.

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.

The circuit shown in Figure 1 is a high performance industrial signal level multichannel data acquisition circuit that has been optimized for fast channel-to-channel switching. It can process 16-channels of single-ended inputs or 8-channels of differential inputs with up to 18-bit resolution.

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.

It is important to provide fast and high resolution conversion information when sampling industrial level signals. Traditionally, the highest resolution analog-to-digital converters (ADCs) available at sampling rates up to 500 kSPS were 14 bit to 18 bit. The circuit shown in Figure 1 is a single-supply system optimized for sampling industrial level signals with a 24-bit, 250 kSPS sigma- delta (Σ-Δ) ADC. Each of the two differential or four pseudodifferential channels can be scanned at a rate up to 50 kSPS with 17.2 bits of noise-free code resolution.

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.

The circuit shown in Figure 1 is a complete high performance resolver-to-digital (RDC) circuit that accurately measures angular position and velocity in automotive, avionics, and critical industrial applications where high reliability is required over a wide temperature range.

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).

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.

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 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.

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).

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.

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.

A growing number of applications require data acquisition systems that must operate reliably at very high ambient temperature environments, such as downhole oil and gas drilling, avionics, and automotive. The circuit shown in Figure 1 is a 16-bit, 600 kSPS successive approximation analog-to-digital converter (ADC) system using devices rated, characterized, and guaranteed at 175°C. Because many of these harsh environment applications are battery-powered, the signal chain has been designed for low power consumption while still maintaining high performance.

This circuit uses the AD7981, a low power (4.65 mW at 600 kSPS), high temperature PulSAR^® ADC, driven directly from the AD8634 high temperature, low power op amp. The AD7981 ADC requires an external voltage reference between 2.4 V and 5.1 V, and in this application, the voltage reference chosen is the micropower ADR225 precision 2.5 V reference, which is also qualified for high temperature operation and has a very low quiescent current of 60 μA maximum at 210°C.

All of the ICs in this design have packaging specially designed for high temperature environments, including monometallic wire bonds. In addition, this reference design describes the selection of the passive components, printed circuit board PCB) materials, and construction techniques to enable operation at these extreme temperatures. A complete design support package including bill of materials, schematic, assembly, and layout files is also available.

The circuit shown in Figure 1 is a high performance, resolver-to-digital converter (RDC) circuit that accurately measures angular position and velocity in automotive, avionics, and critical industrial applications where high reliability is required over a wide temperature range. The AD8397 high current driver can supply 310 mA into a 32 Ω load and eliminates the requirement for discrete push-pull buffer solutions.

Common applications of RDCs are in automotive and industrial markets to provide motor shaft position and/or velocity feedback. 

The circuit shown in Figure 1 is a flexible, integrated, 4-channel thermocouple measurement system based on the Arduino-compatible EVAL-ADICUP360 platform, which contains the ADuCM360 low power, precision analog microcontroller. The ADuCM360 has an ARM Cortex™-M3 processor core, a number of peripherals, and also precision analog functions including a dual, 24-bit, Σ-Δ analog-to-digital converter (ADC); multiplexer; programmable gain amplifier (PGA); and voltage reference.

The circuit can process up to four independent thermocouple channels, and the software linearization algorithms support eight different types of thermocouples (B, E, J, K, N, R, S, and T). The four thermocouples can be connected in any combination, and resistance temperature detectors (RTDs) on each thermocouple channel provide cold junction compensation (CJC). No extra compensation is needed. Thermocouple measurements using this system cover the full operating range of the various types of thermocouples.

The circuit interfaces to the EVAL-ADICUP360 Arduino-compatible platform for rapid prototyping. With a USB to UART interface and open source firmware, the EVAL-CN0394-ARDZ and EVAL-ADICUP360 combination can be easily adapted to a variety of thermocouple applications.

The circuit shown in Figure 1 is a completely self-contained, microprocessor controlled, highly accurate conductivity measurement system ideal for measuring the ionic content of liquids, water quality analysis, industrial quality control, and chemical analysis.

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.

The circuit shown in Figure 1 is a dual-channel colorimeter featuring a modulated light source transmitter, programmable gain transimpedance amplifiers on each channel, and a very low noise, 24-bit Σ-Δ analog-to-digital converter (ADC). The output of the ADC connects to a standard FPGA mezzanine card. The FPGA takes the sampled data from the ADC and implements a synchronous detection algorithm.

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.

The circuit shown in Figure 1 is a high speed photodiode signal conditioning circuit with dark current compensation. The system converts current from a high speed silicon PIN photodiode and drives the inputs of a 20 MSPS analog-to-digital converter (ADC). This combination of parts offers spectral sensitivity from 400 nm to 1050 nm with 49 nA of photocurrent sensitivity, a dynamic range of 91 dB, and a bandwidth of 2 MHz. The signal conditioning circuitry of the system consumes only 40 mA of current from the ±5 V supplies making this configuration suitable for portable high speed, high resolution light intensity applications, such as pulse oximetry.

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.

The circuit shown in Figure 1 is a portable gas detector, using a 4-electrode electrochemical sensor, for simultaneous detection of two distinct gases. The potentiostatic circuit uses an optimum combination of components designed to provide single-supply, low power, and low noise performance, while offering a high degree of programmability to accommodate a variety of sensors for different types of gases.

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.

This circuit, shown in Figure 1, monitors bidirectional current from sources with dc voltages of up to ±270 V with less than 1% linearity error. The load current passes through a shunt resistor, which is external to the circuit. The shunt resistor value is chosen so that the shunt voltage is approximately 100 mV at maximum load current.

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.

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.

The circuit shown in Figure 1 provides two, 16-bit, fully isolated, universal analog input channels suitable for programmable logic controllers (PLCs) and distributed control system (DCS) modules. Both channels are software programmable and support a number of voltage, current ranges, thermocouple, and RTD types, as shown in Figure 1.

The evaluation board contains two different fully isolated universal input channels, one with a 4-pin terminal block (CH2), and one with a 6-pin terminal block (CH1).

For the 4-terminal block channel (CH2), the voltage, current, thermocouple, and RTD inputs all share the same 4 terminals, thus minimizing the number of terminal pins required. For the 6-pin terminal block channel (CH1), the voltage and current inputs share a set of 3 terminals, and the thermocouple and RTD inputs share another set of 3 terminals; this configuration requires more terminals but has a lower part count and component cost. Figure 2 shows a photo of the printed circuit board (PCB), and Figure 3 shows a more detailed schematic of the circuit.

The circuit shown in Figure 1 provides a complete, fully isolated, highly flexible, quad channel analog input system suitable for programmable logic controllers (PLCs) and distributed control system (DCS) applications that require multiple voltage inputs and HART-compatible, 4 mA to 20 mA current inputs.

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.

The circuit shown in Figure 1 is a 16-bit, 300 kSPS successive approximation analog-to-digital converter (ADC) system that has a drive amplifier that is optimized for a low system power dissipation of 10.75 mW for input signals up to 4 kHz and sampling rates of 300 kSPS.

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.

Modern complex systems using various combinations of FPGAs, CPUs, DSPs, and analog circuits typically require multiple voltage rails. In order to provide high reliability and stability, the power system must not only provide the multiple voltage rails but also include proper sequencing control and necessary protection circuits.

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.

The circuit shown in Figure 1 is a flexible, integrated, 4-channel thermocouple measurement system based on the AD7124-8 low power, low noise, precision 24-bit, Σ-Δ analog-to-digital converter (ADC).

The circuit can process up to four independent thermocouple channels, and the software linearization algorithms support eight different types of thermocouples (B, E, J, K, N, R, S, and T). The four thermocouples can be connected in any combination, and resistance temperature detectors (RTDs) on each thermocouple channel provide cold junction compensation (CJC). No extra compensation is needed. Thermocouple measurements using this system cover the full operating range of the various types of thermocouples.

The circuit has a standard serial peripheral interface (SPI) connection to Arduino-compatible platform boards for rapid prototyping. With a USB to UART interface and open source firmware, the EVAL-CN0391-ARDZ can be easily adapted to a variety of thermocouple applications.

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.

The circuit shown in Figure 1 is a single-supply, low noise, portable gas detector, using an electrochemical sensor. The Alphasense CO-AX carbon monoxide sensor is used in this example.

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. 

The circuit shown in Figure 1 is a cost effective, isolated, multi-channel data acquisition system that is compatible with standard industrial signal levels. The components are specifically selected to optimize settling time between samples, providing 18-bit performance at channel switching rates up to approximately 750 kHz.

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.

The circuit shown in Figure 1 measures peak and rms power at any RF frequency from 450 MHz to 6 GHz over a range of approximately 45 dB. The measurement results are converted to differential signals in order to eliminate noise and are provided as digital codes at the output of a 12-bit SAR ADC with serial interface and integrated reference. A simple twopoint calibration is performed in the digital domain.

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.

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.

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.

In power line measurement and protection systems, there is a requirement to simultaneously sample large numbers of current and voltage channels of multiphase power distribution and transmission networks. In these applications, the channel count can vary from as few as six channels to greater than 64 channels. The AD7606 8-channel data acquisition system (DAS) with 16-bit bipolar simultaneously sampling SAR ADCs with on-chip overvoltage protection greatly simplifies signal condi-tioning circuitry and reduces the overall parts count, board real estate, and cost of the measurement and protection board. Even with its high level of integration, each AD7606 requires only nine low value ceramic decoupling capacitors.

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.

The circuit shown in Figure 1 provides a method to convert a high frequency single-ended input signal to a balanced differential signal used to drive the AD7626 16-bit, 10 MSPS PulSAR^® ADC. The circuit maximizes the AD7626 performance for high frequency input tones using the ADA4932-1 low power differential amplifier to drive the ADC. The true benefit of this combination of devices is high performance at low power.

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 in the 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.

Standard single-ended industrial signal levels of ±5 V, ±10 V, and 0 V to +10 V are not directly compatible with the differential input ranges of modern high performance 16-bit or 18-bit single-supply SAR ADCs. A suitable interface drive circuit is required to attenuate, level shift, and convert the industrial signal into a differential one with the correct amplitude and common-mode voltage that match the input requirements of the ADC.

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.

The universal serial bus (USB) is rapidly becoming the standard interface for most PC peripherals. It is displacing RS-232 and the parallel printer port because of superior speed flexibility and support of device hot swap. There has been a strong desire on the part of industrial and medical equipment manufacturers to use the bus as well, but adoption has been slow because there has not been a good way to provide the isolation required for connections to machines that control dangerous voltages or low leakage defibrillation proof connections in medical applications.

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:

1. Directly isolates, in the upstream, the USB D+ and D− lines of a cable.
2. Implements an automatic scheme for data flow of control that does not require external control lines.
3. Provides medical grade isolation.
4. Supports full speed or low speed signaling rates.
5. Supports isolated power delivery through the cable.

The goal of the application circuit shown in Figure 1 is to isolate a peripheral device that already implements a USB interface. It is not possible to make a fully compliant bus-powered cable because there are no 100% efficient power converters to transfer the bus voltage across the barrier. In addition, the quiescent current of the converter does not comply with the standby current requirements of the USB standard. This is all in addition to the speed detection limitations of the ADuM4160. What can be achieved is a fixed speed or switch-controlled speed cable that can supply a modest power to the downstream peripheral. However, it is a custom application that is not completely compliant with the USB standard.

The universal serial bus (USB) is rapidly becoming the standard interface for most PC peripherals. It is displacing RS-232 and the parallel printer port because of superior speed, flexibility, and support of device hot swap. There has been a strong desire on the part of industrial and medical equipment manufacturers to use the bus as well, but adoption has been slow because there has not been a good way to provide the isolation required for connections to machines that control dangerous voltages or low leakage defibrillation proof connections in medical applications.

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.

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:

1. 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.
2. Implements an automatic scheme for data flow of control that does not require external control lines.
3. Provides medical grade isolation.
4. Allows creation of one or more host ports that meet the USB-IF certification standards.
5. Supports full speed signaling rates.
6. 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.

The universal serial bus (USB) is rapidly becoming the standard interface for most PC peripherals. It is displacing RS-232 and the parallel printer port because of superior speed, flexibility, and support of device hot swap. There has been a strong desire on the part of industrial and medical equipment manufacturers to use this bus as well, but adoption has been slow because there has not been a good way to provide the isolation required for connections to machines that control dangerous voltages or low leakage defibrillation proof connections in medical applications.

The ADuM4160 provides an inexpensive and easy to implement isolation buffer for medical and industrial peripherals. The challenges that need to be met are:

1. Isolate directly in the USB D+ and D− lines allowing the use of existing USB infrastructure in microprocessors.
2. Implement an automatic scheme for data flow of control that does not require external control lines.
3. Provide medical grade isolation.
4. Allow a complete peripheral to meet the USB-IF certifi-cation standards.
5. Support full speed (12 Mbps) and low speed (1.5 Mbps) signaling rates.
6. Support flexible power configurations.

The circuit shown in Figure 1 isolates a peripheral device that already supports a USB interface. Because the peripheral is not explicitly defined in this circuit, power to run the secondary side of the isolator has been provided as part of the solution. If the circuit is built onto the PCB of a peripheral design, power could be sourced from the peripheral’s off line supply, a battery, or the USB cable bus power, depending on the needs of the application.

The application circuit shown is typical of many medical and industrial applications.

The circuit block diagram shown in Figure 1 is a low phase noise translation loop synthesizer (also known as an offset loop). This circuit translates the lower 100 MHz reference frequency of the ADF4002 phase locked loop (PLL) up to a higher frequency range of 5.0 GHz to 5.4 GHz, as determined by the frequency of the local oscillator (LO).

The translation loop synthesizer has very low phase noise (<50 fs) in contrast to a synthesizer using only a PLL. The low phase noise is because of the very low N value used by the ADF4002 integer-N PLL, which controls the voltage controlled oscillator (VCO). In this example, the ADF4002 phase frequency detector (PFD) runs at 100 MHz, and N = 1, yielding phase noise performance that is not limited by the N value of the PLL.

The combination of parts shown in Figure 1 provides an ultralow power, 3-axis, motion activated power switch solution capable of controlling up to 1.1 A of load current. The circuit is ideal for applications where extended battery life is critical. When the switch is off, the battery current is less than 300 nA, and when the switch is on, it draws less than 3 μA. The circuit provides an industry leading, low power motion sensing solution suitable for wireless sensors, metering devices, home healthcare, and other portable applications.

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.

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.

Power/Noise Tradeoff

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 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.

When a certain status condition is detected, the pin that condition is mapped to is activated. The configuration of the pin is active high by default, so that when it is activated, the pin goes high. However, this configuration can be switched to active low by setting the INT_LOW pin in the appropriate INTMAP register.

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.

For better visibility, the X-axis and Z-axis plots are disabled using the radio buttons above the chart.

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.

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 common-mode 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.

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.

The circuit shown in Figure 1 uses the ultralow power AD7982 18-bit, 1 MSPS analog-to-digital converter (ADC) driven by the ADA4940-1, a low power fully differential amplifier. The ADR435 low noise precision 5.0 V voltage reference is used to supply the 5 V needed for the ADC. All the ICs shown in Figure 1 are available in small packages, either 3 mm × 3 mm LFCSP or 3 mm × 5 mm MSOP, which helps to reduce board cost and space.

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.

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.

The circuit, shown in Figure 1, is an H-bridge composed of high power switching MOSFETs that are controlled by low voltage logic signals. The circuit provides a convenient interface between logic signals and the high power bridge. The bridge uses low cost N-channel power MOSFETs for both the high and low sides of the H-bridge. The circuit also provides galvanic isolation between the control side and power side. This circuit can be used in motor control, power conversion with embedded control interface, lighting, audio amplifiers, and uninterruptable power supplies (UPS).

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.

The circuit in Figure 1 is a completely isolated, robust, industrial, 4-channel data acquisition system that provides 16-bit, noise free code resolution and an automatic channel switching rate of up to 42 kSPS. The channel to channel crosstalk at 42 kSPS switching is less than 15 ppm FS (less than −90 dB) because of the unique selection of fast settling components in the multiplexed signal chain.

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.

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.

Signal levels in industrial process control systems generally fall into one of the following categories: single-ended current (4 mA-to-20 mA), single-ended, differential voltage (0 V to 5V, 0 V to 10 V, ±5 V, ±10 V), or small signal inputs from sensors such as thermocouples or load cells. Large common-mode voltage swings are also typical, especially for small signal differential inputs; therefore good common-mode rejection is an important specification in the analog signal processing system.

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.

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.