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Data Sheet

AD5940/AD5941

GENERAL DESCRIPTION

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The AD5940 and AD5941 are high precision, low power analog

front ends (AFEs) designed for portable applications that require

high precision, electrochemical-based measurement techniques,

such as amperometric, voltammetric, or impedance measurements.

The AD5940/AD5941 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/AD5941 is designed for electrochemical toxic gas sensing.

The AD5940/AD5941 consist 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 po-

tentiostat. 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/AD5941 measurement channel features a 16-bit, 800

kSPS, multichannel successive approximation register (SAR) ana-

log-to-digital converter (ADC) with input buffers, a built in antialias

filter, and a programmable gain amplifier (PGA). An input multiplex-

er (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 chan-

nels. 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 ultra low leakage, programmable switch matrix connects the

sensor to the internal analog excitation and measurement blocks.

This matrix provides an interface for connecting external transimpe-

dance amplifier resistors (RTIAs) and calibration resistors. The ma-

trix 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/AD5941 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 controlled using the AFE sequencer. The AFE sequencer

allows cycle accurate control of multiple external sensor devices.

The AD5940/AD5941 operate from a 2.8 V to 3.6 V supply and

are specified over a temperature range of −40°C to +85°C. The

AD5940 is packaged in a 56-lead, 3.6 mm × 4.2 mm WLCSP. The

AD5941 is packaged in a 48-lead LFCSP.

AD5941 Datasheet(PDF) 6 Page - Analog Devices

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