About the differential amplifier!

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xzp

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Generally, we use the differential amplifier in the sensor output voltage detection, however, I always saw that there is a 10Meg resistor parallel at the two differential input, why that 10 meg resistor useing here? why not 1Meg or 100Meg?
can anybody give me an explaination?
thank you guys!
 

It is compensation offset currents. As is known, the differential amplifier has Large input resistance, thus at a small offset current on an input, we have the big offset voltage. These resistors applied to neutralization of this effect. The size of resistance is defined by the technology manufacture of a microcircuit and its parameters. The top limit of resistance is limited to size of offset currents, bottom - accuracy of measurement (when this additional resistance starts to influence factor of transfer)
 

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