The ad5941 is a high-precision, low-power analog front-end (AFE) designed for portable applications that require high-precision, electrochemical based measurement technologies such as current, volt ampere or impedance measurement. Ad5941 is specially designed for measuring skin impedance and human impedance. It can also be used in a complete bioelectrical energy / bioelectrical potential measurement system together with ad8233afe.

Ad5941 consists of two high-precision excitation loops and a general measurement channel, which can measure a wide range of sensors. The first excitation loop includes an ultra-low power, dual output string DAC and a low power, low noise potentiostatic amplifier. One output of the DAC controls the non inverting input of the potentiostatic amplifier, and the other output controls the non inverting input of the TIA. This low-power excitation loop can generate signals from DC to 200Hz.

The second excitation loop includes a 12 bit DAC (commonly referred to as high-speed DAC) capable of generating high-frequency excitation signals up to 200 kHz.

The ad5941 measurement channel has a 16 bit, 800ksps multichannel successive approximation register (SAR) ADC with input buffer, built-in anti aliasing filter and programmable gain amplifier (PGA). Its input voltage range is ± 1.35v. The input multiplexer before ADC allows the user to select the input channel for measurement. These input channels include a plurality of external current inputs, a plurality of external voltage inputs, and internal channels. The internal channel is used for diagnostic measurement of internal power supply voltage, bare chip temperature and reference voltage.

The current input includes two transimpedance amplifiers (TIA) with programmable gain and load resistance for measuring different types of sensors. The first TIA is called lptia and is used to measure low bandwidth signals. The second TIA is called high-speed TIA and is used to measure high bandwidth signals up to 200 kHz.

The ultra low leakage current programmable switch matrix is used to connect the sensor to the internal analog excitation and measurement module. It provides an interface for connecting the external TIA gain resistor and the calibration resistor. It can also be used to multiplex multiple electronic measurement kits to the same wearable electrode.

Provide precise 1.8V and 2.5V on-chip reference voltage sources. The internal ADC and DAC circuits use the on-chip reference voltage source to ensure the low drift performance of these peripherals.

The ad5941 measurement module can be controlled by direct register writing through the SPI interface, or by using a programmable timing controller, which can automatically control the AFE chip. 6KB SRAM is partitioned into deep data FIFO and command FIFO. The measurement command is stored in the command FIFO, and the measurement result is stored in the data FIFO. Many FIFO related interrupts are provided to indicate that the FIFO is full.

Many gpios are provided, which can be controlled by AFE timing controller. In this way, multiple external sensor kits can be accurately controlled periodically through the timing controller.

The ad5941 is powered by a 2.7V to 3.6V power supply with a rated temperature range of − 40 ° C to + 85 ° C. The ad5941 uses 48 pin 7 × 7mmlfcsp package.

Performance characteristics and application scope of low power analog front end ad5941

Application:

Electrochemical measurement

Electrochemical gas sensor

Potentiostat / current measurement / volt ampere measurement / cycle

Voltammetric measurement

Bio impedance application

Skin impedance

Body impedance

Continuous blood glucose monitoring

Battery impedance

Responsible editor: GT

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