[sdiy] Weird Serge Resonant Filter topology in upper bands

Lanterman, Aaron D lanterma at ece.gatech.edu
Thu Dec 15 04:40:10 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.

And of course one can as well tap at the + input. Forming a voltage divider between C2/R1 and the NIC reflected R4/C1 impedance.

So I did find a filter that looks like Rene’s filter (which I’m going to call the Rene filter until I find out something else it should be called), namely Figure 7 here on one of Rod Elliott’s pages:


Except Rod’s op amp inputs are flipped relative to Rene’s.

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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