Zero phase shift Op-Amp bandpass filter design

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Discussion Overview

The discussion revolves around the design of a bandpass filter using operational amplifiers (op-amps) that meets specific criteria, including a midband gain of 20 dB and -3 dB frequencies at 20 Hz and 20 kHz, while ensuring zero phase shift. The scope includes theoretical considerations and practical design approaches.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether the midband gain strictly refers to voltage gain, expressing uncertainty about using a common collector amplifier to achieve zero phase shift.
  • Another participant clarifies that gain typically implies voltage gain and suggests that the design should focus on op-amps, emphasizing the need for research on low or zero phase shift filters.
  • A later reply raises the question of whether the zero phase shift requirement is met by using a non-inverting amplifier stage or if it necessitates no phase shift across the entire passband, suggesting that the latter may not be achievable with standard filter designs.
  • Another participant proposes that the zero phase shift requirement indicates a preference for non-inverting circuit designs, such as Sallen-Key topology, over inverting designs.

Areas of Agreement / Disagreement

Participants express differing views on the interpretation of the zero phase shift requirement and its implications for filter design. There is no consensus on whether achieving zero phase shift across the specified frequency range is feasible with standard filter configurations.

Contextual Notes

Participants have not reached a definitive conclusion regarding the feasibility of achieving zero phase shift in the specified bandpass filter design, and there are unresolved assumptions about the implications of the phase shift requirement.

kyle111
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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.

Homework Equations

The Attempt at a Solution

 
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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.
 
gneill said:
You'll want to do some research on low (or zero) phase shift filters.
kyle111 said:
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").
 

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