Application information

TSU111

20/30

DocID029790 Rev 2

5.5

Using the TSU111 with sensors

The TSU111 has MOS inputs, thus input bias currents can be guaranteed down to 10 pA

maximum at ambient temperature. This is an important parameter when the operational

amplifier is used in combination with high impedance sensors.

The TSU111 is perfectly suited for trans-impedance configuration. This configuration allows

a current to be converted into a voltage value with a gain set by the user. It is an ideal

choice for portable electrochemical gas sensing or photo/UV sensing applications. The

TSU111, using trans-impedance configuration, is able to provide a voltage value based on

the physical parameter sensed by the sensor.

5.5.1

Electrochemical gas sensors

The output current of electrochemical gas sensors is generally in the range of tens of nA to

hundreds of µA. As the input bias current of the TSU111 is very low (see Figure 8,

Figure 9, and Figure 10) compared to these current values, the TSU111 is well adapted for

use with the electrochemical sensors of two or three electrodes. Figure 35: "Potentiostat

schematic using the TSU111" shows a potentiostat (electronic hardware required to control

a three electrode cell) schematic using the TSU111. In such a configuration, the devices

minimize leakage in the reference electrode compared to the current being measured on

the working electrode.

Another great advantage of TSU111 versus the competition is its low noise for low

frequencies (3.6 µVpp over 0.1 to 10Hz), and low input offset voltage of 150µV max. These

improved parameters for the same power consumption allow a better accuracy.

Figure 34: Trans-impedance amplifier schematic

TSU111

R

+

-

V ref + RI

V ref

I

Sensor:

electrochemical

photodiode/UV