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INA111: Trouble getting gain for output signals.

Part Number: INA111


I have a INA111BP I am using in a research setting to amplify a signal/reduce noise coming from a non-contact displacement measuring capacitive probe. The probe runs from a coaxial connection to a Capacitec 210-SLC-200Hz pre-amplifer unit, which has two outputs: a signal voltage and ground. So far I have been having trouble getting the amplifier to create gain based on the resistor values placed across pins 1&5.

I have been attempting to test my amplifier on a bread-board with a voltage source and a signal generator. In order to visualize the resulting waveform I have the amplifier outputs(V_o) attached to a digital oscilloscope probe and REF attached to the probes ground. For input voltage my lab has a 12V power source and I have been using a signal generator to feed a sinewave at 200hz into the circuit. 

When the power source(12V) is on feeding into pins 2&3 of the amp and the signal generator +&- leads are connected to pins 4&6 respectively, I can register a sinusoidal function, but the function does not change in amplitude whatsoever when I switch out different resistors into the Rg pins.

Any help on this matter is appreciated. Feel free to ask more about the current setup I have been using.

Thank You,


  • Hi Cam,

    To start I would like to verify that you are making connections to the proper pins, because the connections you have described do not align with the pinout of the INA111 shown below:


    What is the amplitude of your input signal and what is your common-mode input voltage? If you are operating in single supply with a grounded reference your output swing range depends heavily on your input common-mode voltage. The plot below shows these limitations:

    The tool used to generate this plot can be found here: 

    In single supply your inputs need to be biased to some common-mode, preferably mid-supply to maximize your output swing. If your connections are correct then this may be the source of your issue.