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OPA891: opa891 bandwidth issue

li cunxu
Prodigy 140 points

Part Number: OPA891
Other Parts Discussed in Thread: OPA892, OPA814, OPA810

Hi TI expert

The attachment shows the function of adder amplification. Vg2 is a 20 MHz sine wave . The bandwidth of opa891 is 180MHz. The simulation results show that the output waveform is somewhat distorted. Why is the output waveform distorted? Is the op-amp's bandwidth insufficient? 

Thank you! 

opa891 summing amplifier.TSC 

  • 0
    TI__Mastermind 19720 points

    Hi,

    I was able to look over your circuit, and I believe it is showing that the model is slew rate limited. However, I am not sure why this is showing this as the device should have enough slew rate performance for this Vpp and bandwidth. I believe the real device would still have enough large signal bandwidth to handle 20MHz. It is somewhat close in terms of the amount of slew rate needed so a slightly higher performing part would fix this, but I believe the model is limiting the performance.

    Best Regards,

    Ignacio

  • 0 in reply to Ignacio Vazquez Lam1
    Prodigy 140 points

    Hi

    I chose the OPA892 operational amplifier. It has relatively high bandwidth and slew rate. The attachment is my simulation file. When V6 = 5V and Vg2 is a 1V amplitude sine wave, the result shows glitches. Could you advise how to adjust the parameters? Or could you recommend an op-amp that meets the input conditions in the attachment? Thank you!

    opa892 summing amplifier.TSC

  • +1 in reply to li cunxu
    TI__Mastermind 19720 points

    Hi,

    The issue you are seeing glitches with the OPA892, is because you are in a gain of 1V/V which would cause this device to oscillate since the device is decompensated, meaning the device requires a minimum gain to function correctly. In this case, it would likely not work with your application since it does require a minimum gain of 10V/V. I would consider looking into the OPA810. This device should have enough large signal bandwidth for your application. If you will require even more bandwidth or a higher Vpp something like the OPA814 would have more than enough large signal bandwidth for your application.

    Best Regards,

    Ignacio

  • 0 in reply to Ignacio Vazquez Lam1
    Prodigy 140 points

    Hi,

    Thank you for your reply.