Op Amps: The All-PassFilter

[@eavids128]

Your students are really lucky, you're a fantastic professor!

[@simonyoungglostog]

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

[@ajingolk7716]

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

[@daveevans9809]

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]

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]

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]

@@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]

@@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]

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

[@ElectronicswithProfessorFiore]

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]

What is the name of this software

[@ElectronicswithProfessorFiore]

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

[@ViniciusPersondeOliveira]

thanks professor fiore!

[@CatFish107]

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

[@ElectronicswithProfessorFiore]

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]

@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]

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