[sdiy] Weird Serge Resonant Filter topology in upper bands

Lanterman, Aaron D lanterma at ece.gatech.edu
Thu Dec 15 10:39:29 CET 2022

On Dec 13, 2022, at 4:39 AM, René Schmitz <synth at schmitzbits.de<mailto:synth at schmitzbits.de>> wrote:

On 13.12.2022 10:22, René Schmitz wrote:

But if you swap + and -, and tap at the -input, then it works like I'd expect.

Now it starts to look familiar. The opamp forms a negative impedance converter.

I just did some experiments in Falstad. If I try the circuit Rene’s way and eyeball the bandwidth, I get Q factors of around 3, which matches the Qs of the lower bands using the MFB. If I don’t do it Rene’s way, I get Qs of around 2 for the higher two bands.

I think we are zeroing in on something.

Alas, I still can’t get my algebraic analysis to match anything like what’s coming in the simulations, but that’s something else for another time.

Aaron Lanterman, Prof. of ECE, Georgia Tech
My blog on Education and Innovation: https://edupocalypsenow.wordpress.com
My blog on Electronics and Programming: https://lantertronics.blogspot.com
My YouTube channel on Electronics and Programming: https://www.youtube.com/c/lantertronics

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