The AD5940 AFE integrates potentiostat and electrochemical impedance spectroscopy (EIS) functionality into a single chip, providing sensor measurement in the time and frequency domains. It has integrated hardware accelerators for advanced sensor diagnostics and low noise for accurate sensor measurements. The low-power AD5940 has been designed to work with the AD8233 AFE in a complete bioelectric/biopotential measurement system.
An on-chip potentiostat allows for a host of standard electrochemical-based measurement techniques, such as amperometric, voltametric, or impedance measurements. The device consists of two potentiostat loops, a low bandwidth loop that can 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 SAR ADC with input buffers, a built in anti-alias filter (AAF), and a programmable gain amplifier (PGA). 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 SPI interface, or alternatively, by using a pre-programmable sequencer, which provides autonomous control of the AFE chip. 6 kB of SRAM is partitioned for a deep data 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.