# Zero phase shift Op-Amp bandpass filter design

• kyle111

## Homework Statement

"design a band pass circuit having a midband gain of 20 dB with -3 dB frequencies at 20 Hz and 20 KHz the amplifier should not produce any phase shift." does midband gain strictly apply to voltage gain (because that's how i look at it)? I was going to use a common collector amplifier to achieve the 0 phase shift but i don't think i can get the correct gain with that approach. all i really need here is advise or options, i can solve the hard numbers myself I think.

## The Attempt at a Solution

HI kyle111, Welcome to Physics Forums.

Your thread title says "OP AMP" (which is not specific enough for the posting rules, by the way. I'll change it for you this time) so presumably you are meant to design a bandpass filter employing op-amps.

Gain usually implies voltage gain, although there are circuits that purposely convert voltage to current and vice versa and their transfer functions are based on a voltage/current or current/voltage ratio. I think it's safe to say in this case that you are looking at a voltage gain of 20 dB for the passband.

You'll want to do some research on low (or zero) phase shift filters. Once you have a handle on the topic you can show us what you've tried.

You'll want to do some research on low (or zero) phase shift filters.
the amplifier should not produce any phase shift.
It needs to be established whether the zero phase shift criterion is met simply by using an amplifier stage which is itself non-inverting, or whether this specification directs that the filter show no phase shift across its 20Hz - 20kHz passband.

I think the latter is not achievable, not with a standard second or fourth order filter.

I think, the requirement of "zero phase shift" simply means that a non-inverting circuit design is required (for examply: Sallen-Key topology) rather than an inverting amplifier design (as "multi-feedback").