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The 101 of analog signal filtering (2024)

134 points by harperlee

by nativeit

2 subcomments

Thanks for reposting this. I missed it last year, and as an EE with a misspent youth (I originally got a BA in media), I have frequently struggled with the calculus. One of the few regrets is that I didn’t learn advanced math back when my brain was primed for it. Learning calculus in mid-life is tough.

by ErroneousBosh

0 subcomment

I wonder if there's a blog post in the three levels of complexity of calculating Sallen-Key filters?
https://upload.wikimedia.org/wikipedia/commons/3/3f/Sallen-K...
Super simple, really stable, and very easy to calculate. The cutoff frequency and Q can be set independently, and while making the cutoff variable can be tricky (as seen in various analogue synthesizers) you can vary the Q by varying the gain of the amp. If you assume it's just a unity gain buffer (in some designs it's just an emitter follower) getting the component values is easy.

0 subcomment

by immibis

1 subcomments

I don't know why nobody seems to ever begin with: A filter is a voltage divider with frequency-dependent complex impedance.
If you can calculate what a resistor network does, or get a computer to do it, you can also calculate what a filter does (and you'll definitely want a computer for that).
(Going backwards, from a desired frequency response to a filter design, takes more learning. Luckily some very smart people already designed filter templates where you can just plug in the frequency you want)

by wafflesfreak

0 subcomment

Really great intro to this topic -- rc filtering is rarely explained this intuitively.

by dang

0 subcomment

Discussed at the time:
The 101 of analog signal filtering - https://news.ycombinator.com/item?id=40946165 - July 2024 (20 comments)
(p.s. reposts are fine after a year or so; links to past threads are just to satisfy extra-curious readers!)

by aj7

0 subcomment

TI App Notes and their design app, LT Spice, and the late Bob Pease are your friends

by artemonster

0 subcomment