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IN-Amp Offset Corr. Loop, Bypass Capacitors

mahir rahman
Intellectual 350 points
Other Parts Discussed in Thread: INA129

Dear All,

Kindly asking about the bypass capacitors which are not shown in the attached cct.:

1. What is meant by them?

2. The Ref. Pin of the IC INA129E is a nulling pin?

3. If we added a switch in series with R1, is it required to add another switches is series with Ref pin and with the two input pins in order to make offset correction using the auto-zeroing technique?

Please i need help with the above questions.

Best Regards

  • 0
    Guru 21975 points

    Mahir,

    The note about bypass capacitors refers to the capacitors that would be connected from the power supply voltages to ground near the amplifiers. Follow recommendations in the amplifier data sheets. Bypass capacitors are often omitted from circuit diagrams to reduce the "clutter" and focus attention on main aspects of the circuit.

    The Ref pin of a instrumentation amplifier is normally connected to ground. This provides the reference to which the output voltage is referred. In this case, the reference voltage is derived from the integrator circuit, U2. See the INA129 data sheet for details on the Ref pin function.

    A switch could be placed in series with R1. This would allow a "zero on command" type of function. The integrator would hold the Ref voltage when the switch is opened. No additional switch should be used as the voltage on the Ref pin must be held by the integrator after the switch in series with R1 is opened.

    Regards, Bruce.