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INA333: input bias current return path

Kailyn Chen
Genius 9560 points
Part Number: INA333

Hello，

According to the datasheet 8.2.2.5 Input Bias Current Return Path, it describes that: With higher source impedance, using two equal resistors provides a balanced input with possible advantages of lower input offset voltage as a result of bias current and better high-frequency common-mode rejection, so I made a circuit which the signal source impedance is 100Kohm, but the output is not correct, if I changed the internal resistance to 0ohm or connect the resistor to one input like thermalcouple application, the output is right. But it is used to the differential source impedance is low.  Please help to analysis.

8407.INA333.TSC

Best regards

Kailyn

  • 0
    TI__Guru* 77521 points

    Hi Kailyn,

    Here is the equivalent circuit in your source, and it formed a voltage divider the in the input section (reduce the input voltage delta by approx half). The reason is not working because you have very high source impedance for VG1. Typically, voltage generator is an low input impedance source. 

    If you want to simulate the microphone - a higher source impedance, select R12 to 1-2 kohm as source impedance for microphone or hydrophone etc., then simulate the Figure 34.

    If you have more questions, please let us know. 

    Best,

    Raymond

  • 0
    Guru 140200 points

    Hi Kailyn,

    what exactly is your source? How constant is the 100k source impedance?

    Kai