ADI: impedance & potentiostat AFE for biological and chemical sensing

Analog Devices announces the AD5940, a lowest power, highest performance Impedance and electrochemical front end with intelligent autonomous control. The analog front end combines leading levels of integration and performance for potentiostat and impedance-based electrochemical sensor managements. The on-chip potentiostat allows for a host of standard electrochemical-based measurement techniques, such as amperometric, voltametric, or impedance measurements.

The AD5940 is designed to be used in healthcare-related bio-impedance systems for both skin impedance and body impedance measurements, and also to work with the AD8233 AFE in a complete bioelectric/biopotential measurement system.

The analog front end chip can measure Voltage, current and impedance. The device consists of two potentiostat loops, a low bandwidth loop with ability to generate AC signals up to 200 Hz and a high bandwidth loop with ability to generate AC signals up to 200kHz. The ultra-low power Potentiostat consumes 6.5uA in biased mode.

The AD5940 measurement channel features a 16-bit, 800 kSPS, multichannel successive approximation register analog-to-digital converter with input buffers, a built in anti-alias filter (AAF), and a programmable gain amplifier. The ADC features an input voltage range of ±1.35 V. An input mux before the ADC allows the user to select an input channel for measurement. These input channels include multiple external current and voltage inputs, and internal voltage channels. The internal channels enable on chip diagnostic measurements of the internal supply voltages, die temperature, and reference voltages.

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

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