Gas Sensor Amplifier Reference Design

The design is a low-power amplifier for electrochemical cells that uses very little electricity, making it suitable for battery-powered sensors.

There is a growing use of electrochemical cells in both portable and long-life fixed monitoring devices. Examples include glucose monitors, other portable biomedical devices, and long-life battery-powered devices such as carbon monoxide (CO) gas and environmental monitors. Due to their operational requirements, these sensors must be continuously biased to function properly. Power cycling is typically avoided because it can lead to long recovery times, the need for re-zeroing, or potential sensor damage. The optimal approach is to maintain continuous bias on the sensor while power cycling the rest of the device. The reference design from Texas Instruments (TI) presents a micropower amplifier for two- or three-terminal electrochemical cells, consuming less than 1-μA of total supply current, making it suitable for battery-powered or energy-harvested sensor applications. 

Electrochemical cells require a constant bias, necessitating that the amplifier circuit continuously operates to eliminate sensor start-up and settling times. The design is implemented on a PCB compatible with the TI LaunchPad Development Kit platform. This compatibility facilitates testing with an MSP430 ultra-low-power processor, which uses the LaunchPad processor’s analogue-to-digital converters (ADCs) and a liquid crystal display (LCD) for stand-alone functionality. A three-terminal carbon monoxide sensor exemplifies using an electrochemical cell in this setup.

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The design finds applications across various fields, such as electrochemical gas detectors, biotransducers and biosensors, electrochemistry, and galvanostatic. Each area benefits from the design’s precise and reliable measurement capabilities, essential for monitoring, analyzing, and controlling different biochemical and electrochemical processes. These applications are crucial in environmental monitoring, medical diagnostics, chemical research, and energy storage systems.

The reference design details a nano-power, potentiostat-type circuit for electrochemical sensors. It uses a three-terminal CO gas sensor as a demonstration. Still, it can be adapted to accommodate other two-, three-, or four-terminal electrochemical, potentiostatic, or amperometric cells used in gas, industrial, and medical applications. 

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A nano-power amplifier circuit allows the sensor to operate continuously and independently from the monitoring processor, ensuring the sensor remains biased for immediate readings and minimizing start-up and settling times. The LPV802 dual micropower amplifier, chosen for its ultra-low power consumption (typically 320 nA per channel), enables the entire potentiostat circuit to use less than 1 μA of supply current, suitable for continuous operation in battery-powered settings.

The design is implemented on a PCB compatible with the LaunchPad BoosterPack specification, enabling users to use the MSP430 LaunchPad platform to acquire, calculate, log, and display measurement results. The MSP430FR6989 LaunchPad board is selected for its multiple ADC input pins, ultra-low-power mode capability, USB connectivity, and onboard LCD.

TI has tested this reference design. It comes with a bill of materials (BOM), schematics, assembly drawing, printed circuit board (PCB) layout, and more. The company’s website has additional data about the reference design. To read more about this reference design, click here.