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[原创] ADI AD5940高精度电化学测量前端解决方案

关键词:模拟前端(AFE) 传感器 电化学 AD5940

时间:2019-06-25 10:42:35       来源:中电网

ADI公司的AD5940是高精度高阻抗低功耗电化学测量模拟前端(AFE),设计用于需要高精度基于电化学测量技术的手持应用如测量电流,伏安法或阻抗测量.和AD8233 AFE一起,AD5940在完整的生物电或生物电位测量系统用来测量皮肤阻抗和身体阻抗,还可以对电化学毒性气体进行检测.AD5940包括两个高精度激励回路和一个共通的测量通路,可使所测的传感器进行到底各种性能的测试.第一个激励回路包括一个超低功耗双输出串数模转换器(DAC),和一个低功耗低噪音电位仪.DAC的一个输出控制电位仪的非反相输入,另一个输出控制跨导放大器(TIA)的非反相输入,这种低功耗激励回路能产生DC-200Hz的信号.第二个激励回路包括12位DAC,相对比较高的速度,能产生高达200kHz的高频激励信号.AD5940测量通路具有16位800 kSPS多路逐次逼近寄存器(SAR)模数转换器(ADC),具有输入缓冲器,内置抗混淆滤波器和可编增益放大器(PGA),ADC前的输入复接允许用户选择测量输入通路,而输入通路包括多个外部电流输入,外部电压输入和内部通路,它允许内部电源电压,芯片温度和基准的诊断测量.器件工作电压2.8V-3.6V,工作温度−40℃ 到 +85℃.主要用在电化学测量,电化学气体传感器,电位仪/电流仪/伏安法/循环伏安法,生物阻抗应用如皮肤阻抗和身体阻抗,连续葡萄糖监测和电池阻抗.本文介绍了AD5940主要特性,简化框图和功能框图,ADC核框图和多种应用框图,以及EVAL-AD5940BIOZ 生物电评估板和电化学测量评估板EVAL-AD5940ELCZ主要特性,电路图和PCB设计图.

The AD5940 is a high precision, low power analog front end (AFE) designed for portable applications that require high precision, electrochemical-based measurement techniques, such as amperometric, voltammetric, or impedance measurements. The AD5940 is designed for skin impedance and body impedance measurements, and works with the AD8233 AFE in a complete bioelectric or biopotential measurement system. The AD5940 is designed for electrochemical toxic gas sensing.

The AD5940 consists of two high precision excitation loops and one common measurement channel, which enables a wide capability of measurements of the sensor under test. The first excitation loop consists of an ultra low power, dual output string, digital-to-analog converter (DAC), and a low power, low noise potentiostat. One output of the DAC controls the noninverting input of the potentiostat, and the other output controls the noninverting input of the transimpedance amplifier (TIA). This low power excitation loop is capable of generating signals from dc to 200 Hz.

The second excitation loop consists of a 12-bit DAC, referred to as the high speed DAC. This DAC is capable of generating high frequency excitation signals up to 200 kHz.

The AD5940 measurement channel features a 16-bit, 800 kSPS, multichannel successive approximation register (SAR) analog-to-digital converter (ADC) with input buffers, a built in antialias filter, and a programmable gain amplifier (PGA). An input mux in front of the ADC allows the user to select an input channel for measurement. These input channels include multiple external current inputs, external voltage inputs, and internal channels. The internal channels allow diagnostic measurements of the internal supply voltages, die temperature, and reference voltages.

The current inputs include two TIAs with programmable gain and load resistors for measuring different sensor types. The first TIA, referred to as the low power TIA, measures low bandwidth signals. The second TIA, referred to as the high speed TIA, measures high bandwidth signals up to 200 kHz.

An ultralow leakage, programmable switch matrix connects the sensor to the internal analog excitation and measurement blocks. This matrix provides an interface for connecting external RTIAs and calibration resistors. The matrix can also be used to multiplex multiple electronic measurement devices to the same wearable electrodes.

A precision 1.82 V and 2.5 V on-chip reference source is available. The internal ADC and DAC circuits use this on-chip reference source to ensure low drift performance for the 1.82 V and 2.5 V peripherals.

The AD5940 measurement blocks can be controlled via direct register writes through the serial peripheral interface (SPI) interface, or, alternatively, by using a preprogrammable sequencer, which provides autonomous control of the AFE chip. 6 kB of static random access memory (SRAM) is partitioned for a deep data first in, first out (FIFO) and command FIFO. Measurement commands are stored in the command FIFO and measurement results are stored in the data FIFO. A number of FIFO related interrupts are available to indicate when the FIFO is full.

A number of general-purpose inputs/outputs (GPIOs) are available and are controlled using the AFE sequencer, which allows cycle accurate control of multiple external sensor devices.

The AD5940 operates from a 2.8 V to 3.6 V supply and is specified over a temperature range of −40℃to +85℃. The AD5940 is packaged in a 56-lead, 3.6 mm × 4.2 mm WLCSP package.

AD5940主要特性:

Analog input
16-bit, 800 kSPS ADC
Voltage, current, and impedance measurement capability
Internal and external current and voltage channels
Ultralow leakage switch matrix and input mux
Input buffers and programmable gain amplifier
Voltage DACs
Dual output voltage DAC with an output range of 0.2 V to 2.4 V
12-bit VBIAS0 output to bias potentiostat
6-bit VZERO0 output to bias TIA
Ultra low power: 1 μA
1 high speed, 12-bit DAC
Output range to sensor: ±607 mV
Programmable gain amplifier on output with gain settings of 2 and 0.05
Amplifiers, accelerators, and references
 1 low power, low noise potentiostat amplifier suitable for potentiostat bias in electrochemical sensing
1 low noise, low power TIA, suitable for measuring sensor current output
50 pA to 3 mA range Programmable load and gain resistors for sensor output
Analog hardware accelerators
Digital waveform generator
Receive filters
Complex impedance measurement (DFT) engine
1 high speed TIA to handle wide bandwidth input signals from 0.015 Hz up to 200 kHz
Digital waveform generator for generation of sinusoid and trapezoid waveforms 2.5 V and 1.82 V internal reference voltage sources
System level power savings
Fast power-up and power-down analog blocks for duty cycling
Programmable AFE sequencer to minimize workload of host controller
6 kB SRAM to preprogram AFE sequences
Ultra low power potentiostat channel: 6.5 μA of current consumption when powered on and all other blocks in hibernate mode
Smart sensor synchronization and data collection
Cycle accurate control of sensor measurement
Sequencer controlled GPIOs
On-chip peripherals
SPI serial input/output
Wake-up timer
Interrupt controller
Power
2.8 V to 3.6 V supply
1.82 V input/output compliant
Power-on reset
Hibernate mode with low power DAC and potentiostat amplifier powered up to maintain sensor bias Package and temperature range
3.6 mm × 4.2 mm, 56-ball WLCSP
Fully specified for operating temperature range of −40℃ to +85℃

AD5940应用:

Electrochemical measurements
Electrochemical gas sensors
Potentiostat/amperometric/voltammetry/cyclic voltammetry
Bioimpedance applications
Skin impedance
Body impedance
Continuous glucose monitoring
Battery impedance

图1. AD5940简化框图

图2. AD5940功能框图

图3.AD5940 ADC核框图(IN+, REF, GND,和IN−内部节点)

图4.ADC输入通路基本框图

图5.开关矩阵框图-开关连接到高速DAC和高速TIA

图6.AD5940系统时钟架构图

图7.低频2线生物阻抗回路(最大带宽=300Hz)

图8.高频4线生物阻抗回路(最大带宽=200kHz)

图9.电位模式采用宽带宽AFE回路

图10.采用AD5940,AD8232和AD8233的身体组成和ECG系统解决方案

图11.采用AD5940的典型水分析应用

全生物电系统中AD5940和AD8233

The AD5940 is a high precision, ultra low power, analog front end (AFE) system designed to excite and measure the current, voltage, or impedance response of a sensor.

The AD5940 features two high precision measurement loops. An ultra low power, sub 1 kHz loop and a high speed, sub 200 kHz loop allow the AD5940 to precisely measure the impedance of a sensor.

This application note details how to set up the AD5940 and the AD8233 in a full bioelectric system that can perform electrodermal activity (EDA), body impedance analysis (BIA), and electrocardiogram (ECG) measurements through the same set of electrodes.

The hardware used contains the AD5940 evaluation kit; which includes the EVAL-ADICUP3029 Arm® based Arduino form factor microcontroller; the EVAL-AD5940BIOZ evaluation board; and the AD5940 Z test board shown in Figure 12.

图12.AD5940评估板外形图

评估板包括:

• EVAL-ADICUP3029
• EVAL-AD5940BIOZ
• AD5940 Z test board
• ECG cable
• MicroUSB to USB cable


图13.AD5940和AD8233的信号链图

图14.ECG模拟器连接到评估板示意图

图15.生物阻抗信号通路

优化AD5940的电化学测量

The AD5940 is a high precision, ultra low power, analog front end (AFE) system designed to excite and measure the current, voltage, or impedance response of a sensor.

The AD5940 is specifically designed for high precision analysis of electrochemical cells. This application note details how to set up and optimize the AD5940 to perform electrochemical measurements on a typical electrochemical cell.

The hardware used is the AD5940 evaluation kit, which includes the EVAL-ADICUP3029 Arm® Cortex™-M3 microcontroller-based Arduino Uno form factor and the EVAL-AD5940ELCZ, shown in Figure 16.

The following lists the items included in the EVAL-AD5940ELCZ evaluation kit.
•EVAL-AD5940ELCZ evaluation board
•EVAL-ADICUP3029 evaluation board
•Micro USB to USB cable
•Micro USB to crocodile clip cable

图16.评估板EVAL-AD5940ELCZ插到EVAL-ADICUP3029连接图

图17.电化学电池连接到AD5940

图18.EIS框图,测量传感器

图19.测量RCAL

图20.传感器连接到SEO

图21.2线阻抗

1.EVAL-AD5940BIOZ 生物电评估板

AD5940 专为包括体阻分析 (BIA) 和皮肤电活动 (EDA) 在内的生物阻抗应用而设计。该评估套件包括基于 EVAL-ADICUP3029 Arm® Cortex-M3 微控制器的 Arduino Uno 外形板. EVAL-AD5940BIOZ 生物电屏蔽板用来进行生物电测量,包括电化学活性(EDA),体阻抗分析(4线)(BIA),心电图(ECG)和体阻抗分析(2线)(BIOZ-2线)以及用于测量生物阻抗的 AD5940 和用于 ECG 测量的 AD8233以及定制的微型 USB - ECG 卡扣连接器.


图22.EVAL-AD5940BIOZ生物电屏蔽板外形图

图23.EVAL-AD5940BIOZ生物电屏蔽板电路图(1)

图24.EVAL-AD5940BIOZ生物电屏蔽板电路图(2)

图25.EVAL-AD5940BIOZ生物电屏蔽板PCB设计图(1)

图26.EVAL-AD5940BIOZ生物电屏蔽板PCB设计图(2)

图27.EVAL-AD5940BIOZ生物电屏蔽板PCB设计图(3)

图28.EVAL-AD5940BIOZ生物电屏蔽板PCB设计图(4)

图29.EVAL-AD5940BIOZ生物电屏蔽板PCB设计图(5)

图30.EVAL-AD5940BIOZ生物电屏蔽板PCB设计图(6)

图31.EVAL-AD5940BIOZ生物电屏蔽板PCB设计图(7)

图32.EVAL-AD5940BIOZ生物电屏蔽板PCB设计图(8)

图33.EVAL-AD5940BIOZ生物电屏蔽板PCB设计图(9)

图34.EVAL-AD5940BIOZ生物电屏蔽板PCB设计图(10)

2.电化学测量评估板EVAL-AD5940ELCZ

AD5940 专门用于对电化学电池进行高精度分析。该评估套件旨在轻松配置 AD5940,以便在典型的电化学电池上进行电化学测量。该评估套件包括基于 EVAL-ADICUP3029 Arm® Cortex-M3 微控制器的 Arduino Uno 外形板、EVAL-AD5940ELCZ 子板以及定制微型 USB 到鳄鱼线缆,用于将硬件连接到各种化学装置。


图35.电化学测量评估板EVAL-AD5940ELCZ 外形图

图36.电化学测量评估板EVAL-AD5940ELCZ电路图(1)

图37.电化学测量评估板EVAL-AD5940ELCZ电路图(2)
详情请见:
https://www.analog.com/media/en/technical-documentation/data-sheets/AD5940.pdf
https://www.analog.com/media/en/technical-documentation/application-notes/AN-1557.pdf
以及https://www.analog.com/media/en/technical-documentation/application-notes/AN-1563.pdf
https://wiki.analog.com/_media/resources/eval/user-guides/eval-ad5940/hardware/02_050193a_top.pdf
https://wiki.analog.com/_media/resources/eval/user-guides/eval-ad5940/hardware/02_049988b_top.pdf
https://wiki.analog.com/_media/resources/eval/user-guides/eval-ad5940/hardware/08-049988-01-b.pdf
AD5940.pdf
AN-1557.pdf
AN-1563.pdf
02_050193a_top.pdf
02_049988b_top.pdf
08-049988-01-b.pdf

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