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100 dB gain with one OPA1602?

Ethan Winer
Prodigy 30 points
Other Parts Discussed in Thread: OPA1602

I'm designing an audio circuit that needs 100 dB of gain. I plan to use OPA1602 op-amps with two stages, each providing 50 dB of gain. But is there a risk of oscillation with that much gain within one package? I'll also have some ancillary circuits, such as a unity gain low-pass filter. So should I use one half of the 1602 for that? Or is it safe to have 50+50 dB of gain within one dual op-amp package? Thanks!

  • 0
    TI__Genius 15410 points

    Hi Ethan,

    There should be no issue with each amplifier in a dual package having 50dB of gain. Please know that using 50dB of gain will reduce the bandwidth to approximately 110kHz. For more information on why the bandwidth will be reduced check out our TI Precision Lab videos on Bandwidth. Since you state that this will be for an audio application, it might also help to check out the TI Precision Lab videos on Low Distortion Design.

    -Tim Claycomb

  • 0 in reply to Tim Claycomb
    Prodigy 30 points

    Great, thanks Tim. Yes, I understand that this limits the gain at high frequencies. That's why I'm using two stages to get the 100 dB gain needed. My device is for audio frequencies, and it will be restricted to the audible range below 24 KHz anyway with a low-pass filter.

    Thanks again.

    --Ethan

  • 0
    TI__Mastermind 49906 points
    Hi Ethan,

    Packing that much gain into a small area can be done, but it needs to be done carefully.

    Be sure that any shared circuits, such as Vs/2 bias lines and the supply lines, are well bypassed.

    Watch ground loops - keep signal and power grounds (which includes supply bypass cap grounds) separate and use star grounds.

    Keep the input circuits away from from output circuits and shield the input and output lines. Don't let them "see' each other. Filters and other high-impedance circuits can "see" signals from across the board (capacitive coupling). Put a ground plane under the amp so that capacitive coupling between the pins is reduced.

    Regards,
  • 0 in reply to Paul Grohe
    Prodigy 30 points

    Thanks Paul, yes, that's exactly what I was concerned with. I think I'll err on the side of safety and split the gain across two physical packages, and use the other op-amp halves for unity gain filters etc.