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OA1NP, OA2NP, OA4NP

Application information

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4.7

Using the OA1NP, OA2NP, OA4NP series with sensors

The OA1NP, OA2NP, OA4NP series has MOS inputs, thus input bias currents can be

guaranteed down to 5 pA maximum at ambient temperature. This is an important parameter

when the operational amplifier is used in combination with high impedance sensors.

The OA1NP, OA2NP, and OA4NP series is perfectly suited for trans-impedance

configuration as shown in Figure 39. 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 OA1NP, OA2NP, OA4NP series, using

trans-impedance configuration, is able to provide a voltage value based on the physical

parameter sensed by the sensor.

Electrochemical gas sensors

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

hundreds of

A. As the input bias current of the OA1NP, OA2NP, and OA4NP is very low

(see Figure 9, Figure 10, and Figure 11) compared to these current values, the OA1NP,

OA2NP, OA4NP series is well adapted for use with the electrochemical sensors of two or

three electrodes. Figure 40 shows a potentiostat (electronic hardware required to control a

three electrode cell) schematic using the OA1NP, OA2NP, and OA4NP. In such a

configuration, the devices minimize leakage in the reference electrode compared to the

current being measured on the working electrode.

Figure 39. Trans-impedance amplifier schematic