OA1NP Datasheet, PDF (21/31 Pages) STMicroelectronics – Rail-to-rail input and output

OA1NP, OA2NP, OA4NP
Application information
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
,
6HQVRU
HOHFWURFKHPLFDO
SKRWRGLRGH89
5


9UHI 5,
9UHI
*$066*
DocID025993 Rev 2
21/31
31