[sdiy] Passive filters and impedances

[Chris Juried]

Hi all,
Is anyone using Matlab for computer based algebraic computation?   Sincerely,   
  Chris Juried  
Audio Engineering Society (AES) Member  
InfoComm-Recognized AV Technologist
http://www.juriedengineering.com 
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      From: Neil Johnson <neil.johnson71 at gmail.com>
 To: Phil Macphail <phil.macphail at liivatera.com> 
Cc: synthdiy diy <synth-diy at dropmix.xs4all.nl> 
 Sent: Tuesday, November 3, 2015 12:44 PM
 Subject: Re: [sdiy] Passive filters and impedances
   
HI Phil,




An alternative that could be easier to get started with would be to use a series of ABCD matrices. That way you can solve for any number of stages too.


Thanks for stirring up some ancient memories!

After a quick refresher, e.g., http://www.engr.sjsu.edu/rkwok/EE172/Microwave_Network.pdf

and some fun with wxmaxima it is actually quite easy to bash in the equation for the filter, and then you can flip it around to work out the transfer function.  In this case the filter is represented as:

matrix([1,R1],[0,1]).matrix([1,0],[%i*w*C1,1]).matrix([1,R2],[0,1]).matrix([1,0],[%i*w*C2,1]).matrix([1,R3],[0,1]).matrix([1,0],[%i*w*C3,1]).matrix([1,0],[1/Rimp,1]);

and turns into something that has quite a few brackets, and as Murphy would have it the A term has the most.

Cheers,
Neil 
--
http://www.njohnson.co.uk


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