[sdiy] MS 20 FILTER

[Aaron Lanterman]

Let me find my notes and go over them again to formulate a more 
intelligent statement... if I come up with something good, I'll scan my 
derivation and post it...

- Aaron



On Sun, 18 Dec 2005, harrybissell wrote:

> Aaron Lanterman wrote:
>
>
>> I'd be very interested in your results on that. I took a Sallen-Key,
>> replaced the resistors with OTAs, and then couldn't quite make that match
>> up with the schematic... in particular, to do a one-for-one replacement of
>> the transistor that hooks to the voltage buffer/amp, you'd need two OTAs
>> in parallel facing opposite directions, which isn't what's happening there
>> - the equivalent resistor winds up working "one way" and you get a
>> different transfer function.
>
> The two resistors that tune the S-K are replaced by OTA.  If you assume that the
> driving impedance is much lower than the first (input) resistor... it cannot work
>
> both ways, its essentially grounded.  The second resistor is terminated in a cap
> and a high impedance, so that one is essentially 'one way' also.  The MS-20
> feedback starts at a low impedance point, so that sould be pretty much 'one way'
> as well.
>
> I'm not following this (or I'm thinking of the wrong points ?)
>
> H^) harry
>
>>
>>
>> - Aaron
>>
>> -----------------------------------------------------------------------------
>>
>> Dr. Aaron Lanterman, Asst. 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: GCATT 334B
>
>