Node Analysis of 2nd order Sallen-Key question

Thread Starter

Techspec2

Joined Oct 15, 2015
10
Hello,

Im trying to figure out how the author of this ( The Sallen-Key filters (hmc.edu) ) (the very first/top problem)came to the conclusion Va = Vout((Z2+Z4)/Z2)).I was able to come up with same exact node analysis equations,but trying to solve them I get different results.

So: Va-Vout = Vout(Z2/Z4) -----> Va = Vout((Z2+Z4)/Z2)) I would just like to know how they got to this

My: Va = Vout(Z2/Z4) + Vout and simplified version : Va = Vout[(Z2/Z4) + 1]
Im sure im just overthinking this,but any help is appreciated.
 

Thread Starter

Techspec2

Joined Oct 15, 2015
10
I had to stare at it a bit the first time saw it as well.
This makes me feel abit better lol.

The way the author put those 2 equations side-by-side made it more difficult for me.

And I plan on solving it the original way I stated in beg. of post:

Va = Vout[(Z2/Z4) + 1] ,I have 2 nodes and 2 equations , should be do-able,but the author stumped me lol and I need a break.Too many Laplace Transforms and transforms in general.
 

Papabravo

Joined Feb 24, 2006
16,773
I seem to remember that Van Valkenburg (Analog Filter Design, 1982) had an especially lucid description of the analysis of the Sallen-Key topology. I don't remember if it was the 2-pole or the 3-pole, but I'm sure I could dig it up if it would be useful to you.
 

Thread Starter

Techspec2

Joined Oct 15, 2015
10
I seem to remember that Van Valkenburg (Analog Filter Design, 1982) had an especially lucid description of the analysis of the Sallen-Key topology. I don't remember if it was the 2-pole or the 3-pole, but I'm sure I could dig it up if it would be useful to you.
If you want too then heck yeah,But I didnt know this book existed thanks! Gunna buy soon. Its nice to check your work compared to others as a triple check.
 
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