[sdiy] MS 20 FILTER

[Aaron Lanterman]

That's if the file ever actually uploads. Network is slow...

- Aaron


On Mon, 19 Dec 2005, Aaron Lanterman wrote:

>
> On Sun, 18 Dec 2005, harrybissell wrote:
>
>> 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.
>
> Ah, I think I found something describing what I'm thinking of.
>
> Check out this paper, which I've temporarily put up at
>
> users.ece.gatech.edu/~lanterma/00055014.pdf
>
> Fig 1.b is a direct resistor-OTA replacement - three OTAs are used
>
> Fig 1.c is a two-OTA version, which is what I think people on the list 
> generally call an OTA Sallen Key.
>
> According to Table 1, they have different transfer functions - and that's 
> just for a version where the VCVS has unity gain...
>
> I think the issue is the "pretty much" in the feedback path...
>
> - 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
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>
>