+

VREF

CE

WE

RE

Potentiostat (Bias Loop)

+

RF

Transimpedance Amplifier (I to V conversion)

RL

CO Sensor

VTIA

U1

U2

ISENS

R2

10 NŸ

C1

0.1µF

VREF

2.5V

Riso

49.9 k

C2

1µF

R1

10 k

15

TLV6003

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SLOS981 – OCTOBER 2019

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8.2 Typical Application

Figure 32 shows a simple micropower potentiostat circuit for use with three-terminal unbiased CO sensors;

although, the design is applicable to many other type of three-terminal gas sensors or electrochemical cells.

The basic sensor has three electrodes: the sense or working electrode (WE), counter electrode (CE) and

reference electrode (RE). A current flows between the CE and WE proportional to the detected concentration.

The RE monitors the potential of the internal reference point. For an unbiased sensor, the WE and RE electrodes

must be maintained at the same potential by adjusting the bias on CE. Through the potentiostat circuit formed by

U1, the servo feedback action maintains the RE pin at a potential set by VREF.

R1 maintains stability due to the large capacitance of the sensor.

C1 and R2 form the potentiostat integrator and set the feedback time constant.

U2 forms a transimpedance amplifier (TIA) to convert the resulting sensor current into a proportional voltage. The

transimpedance gain, and resulting sensitivity, is set by RF according to Equation 1.

VTIA = (–I * RF) + VREF

(1)

RL is a load resistor with a value that is normally specified by the sensor manufacturer (typically, 10 Ω). The

potential at WE is set by the applied VREF.

Riso provides capacitive isolation and, combined with C2, form the output filter and ADC reservoir capacitor to

drive the ADC.

Figure 32. Three Terminal CO Gas Sensor