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OPA656 Transimpedance amplifier

Other Parts Discussed in Thread: TEST, DEM-OPA-SO-1A, OPA656


I need a transimpedance amplifier to connect output voltage of AC resistors (value from 10 mohm to 1000 ohm) to PXI 4461 that has 1 MΩ || 217 pF on the inputs. The frequency of interest is 50-100 kHz.

I am new to amplifiers, so I guess I need a unity gain amplifier (OPA656 looks good to me) conected as transimpedance amplifier. That looks simple, and I plan to use DEM-OPA-SO-1A to test everything. I know I don't need any resistor in the return path, but my question is do I need any other components (capacitors or resistors connected such as from positive to ground), etc...

And also, is OPA656 fit for purpose or is there any better amplifier to do the job. Is evaluation board DEM-OPA-SO-1A OK to test it?

Thanks for all the help


  • Hello Neven,
    Can you please send me a schematic of what you are trying to achieve. I don't know what an AC resistor is.
  • AC resistor is just like any other resistor, it just needs to work on higher frequencies (non inductive and non apacitive design). The problem is that its value (in ohms) is too high for ADC, and I need to separate it with buffer amplifier (unity gain).
  • Hello Neven,

      In your previous comments you mentioned you would like to configure the amplifier as a unity gain buffer and then you also mentioned a transimpedance amplifier (TIA). I am not sure why you want to configure this as a TIA since that is only needed when converting a current to a voltage. The feedback resistor in a TIA circuit has an effect on its stability so unless you are converting current to voltage I would go with a simple unity gain buffer which directly shorts the output of the amplifier to its inverting input.