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INA597: differential amplifier with 2 op amp up to 2 MHz

Ahmed Ahmed38
Prodigy 240 points
Part Number: INA597
Other Parts Discussed in Thread: INA821

Hello

i am looking to the layout attached. its a differential amplifier based on 2 op amp and a variable resistor to balance a DUT. Could you please advice a circuit and opamp that could do the function up to 2-3 MHz..

best regards

  • 0
    TI__Genius 10850 points

    Hi Ahmed,

    Thank you for your post. The INA597 is a difference amplifier with high value input resistances. If you are trying to measure large currents, like in the ampere range, then a difference amplifier or an instrumentation amplifier will be okay.

    However, if the measured current is very small, like in the uA or mA range, you will need to take a look at an instrumentation amplifier.

    The INA821 may be a good option for you as it is a high precision instrumentation amplifier with 4.7MHz of bandwidth: http://www.ti.com/lit/ds/symlink/ina821.pdf

    -Tamara

  • 0 in reply to Tamara M Alani
    Prodigy 240 points

    Dear Tamara

    thank you for your feedback, i tried to simulate waveform using TINA at high frequency 2MHz but i am getting strange output. my purpose is to balance R2 via R1 to get vout 1 =Vout2 for frequency omega (here 1000 Hz and 2 MHz). I also get an unusual peak at the onset. R2 will be devices with resistance in the range 20 - 90 ohms so i need to have R1 as a potentiometer to balance and cancel out the output. i added some capacitors at the power supply but it doesnt improve the waveform. any suggestions welcome.i attached some files if can help.

    Regards

    Ahmed

    1325.diff amp.TSC

  • 0 in reply to Ahmed Ahmed38
    TI__Genius 10850 points

    Hi Ahmed,

    Thanks for your reply.

    • How exactly are you simulating this circuit? I'd like to re-create your simulation so that I can see what you mean by "strange output".
    • R2 will vary anywhere between 20-90ohms and you want R1 to change with it so that Vout1=Vout2, is that correct?
    • What is Vin? 

    1325.diff amp from Ahmed.TSC

    -Tamara

  • 0 in reply to Tamara M Alani
    Prodigy 240 points

    Dear Tamara ,

    thanks for your feedback. for vin typcally can be a volt or less i used 500mV but the frequency is omega, this is the harmonic i want to cancel out owing to the differential opAmp circuit. i am only interestd in the 3rd harmonic originating from the DUT R1. I simulated using a steady state solver for 1ms. the R1 is a device that shows variability between most likely 20 to 90 ohms. to balance that signal so that the resulting vout=0 i balance with a potentiometer as R2 ( here i just used fixed values) but when i run the simulations i get a transient not sure if it is related to the op Amp or solver. also could you advice on the capacitors are they necessary?

    best regards