5V single power supply 8-channel data acquisition system circuit design

　　Circuit Functionality and Benefits: The circuit shown in Figure 1 is a highly integrated, 16-bit, 1 MSPS, multiplexed, 8-channel, flexible digital acquisition system (DAS) with an integrated programmable gain instrumentation amplifier (PGIA) capable of handling the full range of industrial-grade signals. A single +5 V supply powers the circuit, and a high-efficiency, low-ripple boost converter generates ±15 V to handle differential input signals up to ±24.576 V (±2 LSB INL maximum, ±0.5 LSB DNL typical). For high-precision applications, this compact, economical circuit provides high accuracy and low noise performance. The successive approximation register (SAR)-based data acquisition system incorporates true high-impedance differential input buffers, eliminating the need for additional buffering, which is typically used to reduce kickback in capacitive digital-to-analog converter (DAC)-based SAR analog-to-digital converters (ADCs). In addition, the circuit features high common-mode rejection, eliminating the need for an external instrumentation amplifier, which is typically required in applications where common-mode signals are present.

　　The ADAS3022 is a complete 16-bit, 1 MSPS data acquisition system that integrates the following components: an 8-channel, low-leakage multiplexer; a programmable gain instrumentation amplifier stage with 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 power consumption at the end of each conversion cycle, so the operating current and power consumption scale linearly with throughput, making it ideal for low sampling rate battery-powered applications. The ADAS3022 integrates 8 inputs and 1 COM input; the COM input can be configured as 8 single-ended channels, 8 channels referenced to the same reference voltage, 4 differential channels, or different combinations of single-ended and differential channels. In the circuit shown in Figure 1, the ADR434 low-noise reference buffered by the AD8031 op amp provides the reference voltage. The AD8031 is ideal for use as a reference buffer because it can drive dynamic loads with fast recovery.

　　The ADP1613 is a dc-to-dc step-up converter with an integrated power switch that provides the ADAS3022 with the ±15 V high voltage supplies required for the on-chip input multiplexer and programmable gain instrumentation amplifier without sacrificing the performance of the ADAS3022. This circuit uses a combination of the ADAS3022, ADP1613, ADR434, and AD8031 precision devices to provide both high accuracy and low noise performance.

　　Circuit Description: The first complete DAS on a single chip, capable of converting at rates up to 1 MSPS and accepting differential analog input signals up to ±24.576 V. The device requires high voltage bipolar supplies: ±15 V (VDDH and VSSH), +5 V (AVDD and DVDD), and +1.8 V to +5 V (VIO). The ADAS3022 simplifies the design challenges of a precision 16-bit, 1 MSPS DAS by eliminating the need for signal buffering, level shifting, amplification, noise suppression, and other analog signal conditioning found in standard solutions. In addition, the ADAS3022 offers improved timing and noise performance at higher data rates, smaller size, faster time to market, and lower price.

　　The ADAS3022 integrates a PGIA that can be set to gain 0.16, 0.2, 0.4, 0.8, 1.6, 3.2, and 6.4, and it can handle fully differential input ranges of ±24.576 V, ±20.48 V, ±10.24 V, ±5.12 V, ±2.56 V, ±1.28 V, and ±0.64 V, respectively. The input range is referenced to an internal 4.096 V reference voltage source. It can measure pseudo differential, unipolar, and bipolar input ranges relative to the input voltage on the COM pin. In the circuit shown in Figure 1, the external reference voltage is provided by the 4.096 V ADR434. The ADR434 has the characteristics of high precision, low power consumption (operating current is 800 A), low noise, ±0.12% maximum initial error, and excellent temperature stability. The AD8032 low power operational amplifier for buffering external reference voltages is an ideal choice for battery-powered systems with high bandwidth requirements or high-speed systems with high component density and low power consumption. The ADAS3022 digital interface consists of asynchronous inputs (CNV, RESET, PD, and BUSY) and a 4-wire serial interface (CS, SDO, SCK, and DIN) compatible with SPI, FPGA, or DSP for reading back conversion results and programming configuration registers.