原标题：ADI AD4020低噪音高速20位SAR差分ADC解决方案

　　ADI公司的AD4020是低噪音低功耗高速20位1.8MSPS精密逐次逼近型寄存器(SAR)模数转换器(ADC),具有易用特性,可降低信号链的功耗和复杂性,支持较高的通道密度.采用1.8 V电源供电,具有±VREF全差分输入范围(2.4 V至5.1 V),实现最大±3 ppm积分非线性(INL),保证20位无失码和100.5 dB典型信噪比(SNR),主要用在自动测试设备(ATE),机器自动化,医疗设备,电池供电设备和精密数据采集系统.本文介绍了AD4020主要特性,功能框图,多种应用框图,以及评估板EVAL-AD400xFMCZ/EVAL-AD4020FMCZ主要特性,框图,电路图,材料清单和PCB设计图.

　　The AD4020 is a low noise, low power, high speed, 20-bit, 1.8 MSPS precision successive approximation register (SAR) analog-to-digital converter (ADC). It incorporates ease of use features that lower the signal chain power, reduce signal chain complexity, and enable higher channel density. The high-Z mode, coupled with a long acquisition phase, eliminates the need for a dedicated high power, high speed ADC driver, thus broadening the range of low power precision amplifiers that can drive this ADC directly, while still achieving optimum performance. 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 low serial peripheral interface (SPI) clock rate requirement reduces the digital input/output power consumption, broadens processor options, and simplifies the task of sending data across digital isolation.

　　Operating from a 1.8 V supply, the AD4020 has a ±VREF fully differential input range with VREF ranging from 2.4 V to 5.1 V. The AD4020 consumes only 15 mW at 1.8 MSPS with a minimum SCK rate of 71 MHz in turbo mode and achieves ±3.1 ppm integral nonlinearity (INL), guaranteed no missing codes at 20 bits with 100.5 dB typical signal-to-noise ratio (SNR). The reference voltage is applied externally and can be set independently of the supply voltage.

　　The SPI-compatible versatile serial interface features seven different modes including the ability, using the SDI input, to daisy-chain several ADCs on a single 3-wire bus, and provides an optional busy indicator. The AD4020 is compatible with 1.8 V, 2.5 V, 3 V, and 5 V logic, using the separate VIO supply.

　　The AD4020 is available in a 10-lead MSOP or a 10-lead LFCSP with operation specified from −40℃ to +125℃. The device is pin compatible with the 18-bit, 2 MSPS AD4003.

　　AD4020主要特性:

　　Throughput: 1.8 MSPS maximum

　　INL: ±3.1 ppm maximum

　　Guaranteed 20-bit no missing codes

　　Low power

　　9.0 mW at 1.8 MSPS (VDD only)

　　83 μW at 10 kSPS, 15 mW at 1.8 MSPS (total)

　　SNR: 100.5 dB typical at 1 kHz, 99 dB typical at 100 kHz

　　THD: −123 dB typical at 1 kHz, −100 dB typical at 100 kHz

　　Ease of use features reduce system power and complexity

　　Input overvoltage clamp circuit

　　Reduced nonlinear input charge kickback

　　High-Z mode

　　Long acquisition phase

　　Input span compression

　　Fast conversion time allows low SPI clock rates

　　SPI-programmable modes, read/write capability, status word

　　Differential analog input range: ±VREF

　　0 V to VREF with VREF from 2.4 V to 5.1 V

　　Single 1.8 V supply operation with 1.71 V to 5.5 V logic interface

　　SAR architecture: no latency/pipeline delay

　　Valid first accurate conversion

　　Guaranteed operation: −40℃ to +125 ℃

　　Serial interface: SPI/QSPI/MICROWIRE/DSP compatible

　　Ability to daisy-chain multiple ADCs and busy indicator

　　10-lead packages: 3 mm × 3 mm LFCSP, 3 mm × 4.90 mm MSOP

　　AD4020应用:

　　Automatic test equipment

　　Machine automation

　　Medical equipment

　　Battery-powered equipment

　　Precision data acquisition systems

　　图1.AD4020功能框图

　　图2.AD4020多电源典型应用框图

　　图3.AD4020单电源典型应用框图

　　图4.AD4020带全差分放大器的典型应用框图

　　图5.AD4020带全差分放大器用于单端/差分转换的典型应用框图

　　评估板

　　EVAL-AD4000FMCZ/EVAL-AD4001FMCZ/EVAL-AD4003FMCZ/EVAL-AD4020FMCZ The AD4000/AD4001/AD4003/AD4020 family evaluation board covers the ease of use, 16-/18-/20-bit, precision successive approximation register (SAR) analog-to-digital converters (ADCs). The AD4000/AD4001/AD4003/AD4020 are low power, 16-bit/ 18-bit/20-bit, precision SAR ADCs that offer very high performance with throughputs up to 2 MSPS (1.8 MSPS for the AD4020). The evaluation board is designed to demonstrate the performance of the AD4000/AD4001/AD4003/AD4020 family of ADCs and to provide an easy to understand interface for a variety of system applications. A full description of these products is available in their respective data sheets, which must be consulted when using this evaluation board.

　　The EVAL-AD4000FMCZ/EVAL-AD4001FMCZ/EVAL-AD4003FMCZ/EVAL-AD4020FMCZ evaluation boards are ideal for use with the Analog Devices, Inc., high speed system demonstration platform (EVAL-SDP-CH1Z). These evaluation boards interface to the SDP-H1 board via a 120-pin connector. SMA connectors, JP2 and JP3, are provided for the low noise analog signal source.

　　On-board components include a high precision buffered band gap 5.0 V reference (the ADR4550), a reference buffer (the ADA4807-1), a common-mode buffer (the ADA4807-1), a signal conditioning circuit with two op amps (the ADA4807-1), and a power supply to derive the necessary voltage levels to supply all voltage needs.

　　The EVAL-AD4000FMCZ, EVAL-AD4001FMCZ, and EVAL-AD4003FMCZ are populated with the AD4000, AD4001, and AD4003, respectively. However, these boards can be used to evaluate the performance of the AD4004, AD4005, AD4007, and AD4011 by limiting the sample rate in the evaluation software to the maximum sample rate of the specific ADC. For example, the AD4000 on the EVAL-AD4000FMCZ can be used to evaluate the performance of the AD4004 if the sample rate is limited to 1 MSPS. See the data sheet of each product for its corresponding evaluation board.

　　评估板EVAL-AD4020FMCZ主要特性:

　　Fully featured evaluation board for 10-lead precision ADCs

　　Versatile analog signal conditioning circuitry

　　On-board reference, reference buffers, and ADC drivers

　　PC software for control and data analysis of time and frequency domain

　　System demonstration platform-compatible (EVAL-SDP-CH1Z)

　　EVALUATION BOARD KIT CONTENTS

　　AD4000/AD4001/AD4003/AD4020 evaluation board (see Table 6)

　　12 V wall adapter power supply

　　图6.评估板EVAL-AD4020FMCZ外形图

　　评估板EVAL-AD4020FMCZ材料清单: