Op Amps: The All-PassFilter

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The all-pass filter provides a gain of unity (0 dB) across all frequencies and is not designed to remove any part of the spectrum on its own. Instead, the circuit provides a falling phase shift across the spectrum. It can be used to create quadrature signals (i.e., signals that are +/- 90 degrees out of phase with the input), time delays, and the like. Both lead and lag versions are possible. Here, we examine a simple first-order implementation.
References: Operational Amplifiers and Linear Integrated Circuits: Theory and Application; Chapter 11.
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6 фев 2023

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Комментарии : 16

@simonyoungglostog Год назад

Fascinating. I wish I could articulate the questions I have. I think I'll wait until we've journeyed a little further. Thanks again.

@ViniciusPersondeOliveira Год назад

thanks professor fiore!

@ajingolk7716 Месяц назад

So r3 and c1 determine the phase shift, for 120 deg at 100khz what would be the values? Thank you.

@daveevans9809 Год назад

A question for students - if you feed the ac input signal to a leading and lagging all-pass filter in parallel, then use a third op amp as a summing amplifier, what will the output be? And will it be the same for all frequencies within the RC filter range? Try it!

@siarez Месяц назад

Thank you for the video. I have a question. Here both filters have a descending phase as frequency increases. That is one filter goes from 0 to -180 and one from 180 to 0. Is it possible to have an ascending phase all-pass filter? (e.g a filter that goes from -180 to 0)

@ElectronicswithProfessorFiore Месяц назад

If I understand you correctly, you're asking for the same sort of circuit but with a positive slope, right? I am not sure that you could make one as simple as this little first order circuit. I'd have to think about that for a bit. I can't recall seeing one.

@siarez Месяц назад

@@ElectronicswithProfessorFiore Yes, exactly. I'm looking for such allpass filter because I want to cancel out the phase shift caused by a preceding highpass filter. If possible then we can get a hp filter with flat phase response. But maybe such allpass filter is impossible in principle?

@ElectronicswithProfessorFiore Месяц назад

@@siarez It sounds like what you want is constant group delay or linear phase for your filter. In that case, I'd suggest looking at standard active filters using a Bessel alignment instead of the usual Butterworth (check the videos in the Op Amps playlist or chapter 11 of my free op amps text). A 2nd order Sallen & Key wouldn't be much more complicated than the circuit in the video above (as in another cap and maybe another resistor).

@terrycaster4976 Год назад

Can you please provide a link to the previous video that you mentioned.

@ElectronicswithProfessorFiore Год назад

Sorry about that. I had a little technical glitch with that video. It should be up within a week. In the meantime, you can read the section on the adjustable inverter-noninverter in my op amps text. Remember, it's a free download- see link in the video description above.

@Harsh-ey2sh 2 месяца назад

What is the name of this software

@ElectronicswithProfessorFiore 2 месяца назад

TINA-TI, the free version of TINA available from ti.com

@CatFish107 9 месяцев назад

Maaaan, I wish they were just called phase shifters. That would make it easier to understand from the get go.

@ElectronicswithProfessorFiore 8 месяцев назад

Yeah, it's just a matter of perspective. When most people think of filters, they think in terms of the amplitude (magnitude) response, so calling these "all -pass" makes a certain amount of sense. Of course, forgetting that filters also have a phase response can result in no end of difficulties...

@CatFish107 8 месяцев назад

@ElectronicswithProfessorFiore thanks for the reply. I'm just kind of stumble bumbling my way around, trying to satisfy my curiosity about different types of filters. I am approaching this from a perspective of "I'm curious and want to learn more about this synthesizer component" There sure does seem to be a bounty of learning videos on this tube.

@ElectronicswithProfessorFiore 8 месяцев назад

@@CatFish107 True, but some of them are questionable because nothing is curated by "the algorithm" in terms of accuracy, so be careful.