Analog Devices introduces new impedance and potentiostat analog front ends for biological and chemical sensing

     Analog Devices introduces a new electrochemical and impedance measurement front end that enables the next generation of vital sign monitoring devices and smart electrochemical sensors. The AD5940 analog front end integrates potentiostat and electrochemical impedance spectroscopy (EIS) capabilities in a single chip, enabling sensor measurements in both the time and frequency domains. The device features an integrated hardware accelerator 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 the use of multiple ics to achieve similar performance, ADI's single-chip solution offers system accuracy and dimensional flexibility to measure 2-pin, 3-pin, and 4-pin electrochemical sensors. It 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 sign 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 offers a leading level of integration and performance for potentiostat and impedance-based electrochemical sensor management. The on-chip potentiostat enables the use of a range of electrochemical based standard measurement methods, such as current, voltage, or impedance measurement. Designed for use with the AD8233AFE in complete bioelectrical/biopotential measurement systems for healthcare relevant bioimpedance and human impedance measurements.

     The analog front-end chip is capable of measuring voltage, current and impedance. 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 that can generate AC signals up to 200 kHz. The current consumption of the ultra-low power potentiostat in bias mode is only 6.5uA.

     The AD5940 measurement channel features a 16-bit, 800 kSPS, multi-channel successive approximation register (SAR) analog-to-digital converter (ADC) with input buffer, a built-in anti-aliasing 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 as well as internal voltage channels. The internal channel enables on-chip diagnostic measurement of internal power supply voltage, chip temperature and reference voltage.

     The AD5940 measurement module can be controlled by direct register writing (done via the serial peripheral interface SPI), or by using a pre-programmed timing controller that provides autonomous control of the AFE chip. The 6 kB static random access memory (SRAM) is divided into deep data first-in first-out (FIFO) and command memory. The measurement commands are stored in the command memory and the measurement results are stored in the data FIFO. Many FIFO-related interrupts can be used to indicate the state of the FIFO.