TSZ121 datasheet(23/38 Pages) STMICROELECTRONICS

23 / 38 page

TSZ121, TSZ122, TSZ124

Application information

DocID023563 Rev 5

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The output voltage is calculated using Equation 2:

Equation 2

As the current delivered by the O2 sensor is extremely low, the impact of the Vio can

become significant with a traditional operational amplifier. The use of the chopper amplifier

of the TSZ121, TSZ122, or TSZ124 is perfect for this application.

In addition, using TSZ121, TSZ122, or TSZ124 devices for the O2 sensor application

ensures that the measurement of O2 concentration is stable even at different temperature

thanks to a very good ΔV

io/ΔT.

5.11.2

Precision instrumentation amplifier

The instrumentation amplifier uses three op amps. The circuit, shown in Figure 48:

"Precision instrumentation amplifier schematic", exhibits high input impedance, so that the

source impedance of the connected sensor has no impact on the amplification.

Figure 48: Precision instrumentation amplifier schematic

The gain is set by tuning the Rg resistor. With R1 = R2 and R3 = R4, the output is given by

Equation 3.

Equation 3

The matching of R1, R2 and R3, R4 is important to ensure a good common mode rejection

ratio (CMR).

ou t

–

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