ADI's New Electrochemical and Impedance Measurement Front End Keeps Wearable Devices "Always On"

The AD5940 analog front end integrates potentiostat and electrochemical impedance spectroscopy (EIS) functions in a single chip, enabling sensor measurements in both the time and frequency domains. The device features integrated hardware accelerators for advanced sensor diagnostics, best-in-class low noise performance for accurate sensor measurements, and is designed for “ always on ” wearable applications.

Compared to traditional discrete solutions that have limitations and require multiple ICs to achieve similar performance, ADI's single-chip solution has advantages in system accuracy and size flexibility, and can measure 2-pin, 3-pin, and 4-pin electrochemical sensors. This is an ideal solution for applications where high-precision biological and chemical sensing is mission-critical, such as industrial gas detection, liquid analysis, material sensing, vital signs monitoring, impedance spectroscopy, and disease management.

The AD5940 is an extremely low power, high performance impedance and electrochemical front end with intelligent autonomous control. This analog front end combines leading integration and performance levels for potentiostats and impedance-based electrochemical sensor management. The on-chip potentiostat allows for a range of standard electrochemical-based measurement methods such as current, voltage, or impedance measurements.

The AD5940 is designed for use in healthcare-related bioimpedance systems for skin impedance and body impedance measurements, and is used in conjunction with the AD8233AFE in a complete biopotential/biopotential measurement system.

The AD5940 is capable of measuring voltage, current, and impedance. The device includes two potentiostat loops: a low bandwidth loop that can generate AC signals up to 200 Hz, and a high bandwidth loop that can generate AC signals up to 200 kHz. The ultra-low power potentiostat consumes only 6.5uA in bias mode.

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 antialiasing filter (AAF), and a programmable gain amplifier (PGA). The ADC has an input voltage range of ±1.35 V. An input multiplexer located 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 internal supply voltages, chip temperature, and reference voltages.

The AD5940 measurement blocks can be controlled using direct register writes (done via the serial peripheral interface SPI) or by using a preprogrammed timing controller that provides autonomous control of the AFE chip. The 6 kB of static random access memory (SRAM) is divided into 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 the status of the FIFO.

The AD5940 is available in a 3.6 mm x 4.2 mm, 56-ball WLCSP package. Samples and products are available now. To view the AD5940 product page, download the data sheet, or request samples, please click "Read More ".