[sdiy] Poles of a diode ladder filter

[Aaron Lanterman]

> Are you going to talk about the ladder pole positions, and the pattern
> they make when feedback is applied?  Excellent.

That's actually in an earlier lecture, when I talked about a four-pole 
OTA-C-buffer cascade (i.e. SSM2040) - but I'll mention the same math 
applies. I haven't post that lecture yet since I showed some clips from 
some DVDs at the end of it, and I would be pushing the "educational fair 
use" clause to far for me to post it for the general populus. I need to 
figure out how to edit them out before I post it.

> Someone would have to be nuts to do that... Oh yeah, I did that and
> posted the result to SDIY ten years ago.  I've included a copy of the
> message below.

> Yeah, you got it right (or you made the same mistakes I did).

>  Vout              1
>  ---- = ----------------------------
>   Vin   s^4 + 7s^3 + 15s^2 + 10s + 1

Awesome!
>
> (I *think* this is correct.  If anybody cares they can do it out
> independently and we'll compare notes.)

Well, we've at least got two people saying that's the function. :)

When I derived it, I did it for general impedances, and then plugged in
R and 1/sC as needed,  under the hope that doing everything in Zs at first 
would make the algebra less error prone.

> At a feedback gain of 5:
>   3.25 Hz (Q= 0.51), 0.75 Hz (Q= 1.25)

Oh, I didn't think about thinking about it in terms of looking at the Q of 
the two bandpass sections... interesting...

My lecture tomorrow will probably be pretty short - I'm so overdue on a 
report for on one of my sponsored projects (not even remotely music 
related) that I've gone from "overdue" to "delinquent," so I'm trying to 
knock that out tonight...

  - Aaron

-----------------------------------------------------------------------------

Dr. Aaron Lanterman, Asst. Prof.
and Demetrius T. Paris Junior Prof.    Voice:  404-385-2548
School of Electrical and Comp. Eng.    Fax:    404-894-8363
Georgia Institute of Technology        E-mail: lanterma at ece.gatech.edu
Mail Code 0250                         Web:    users.ece.gatech.edu/~lanterma
Atlanta, GA 30332                      Office: Centergy 5212