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2nd order low pass filter
- Thread starter The_Cook
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Here is a link to a derivation of the unity gain version. Non-unity gain is discussed at the end.
http://en.wikipedia.org/wiki/Sallen_key
ak
http://en.wikipedia.org/wiki/Sallen_key
ak
Would you mind explaining what a unity gain is, and if that applies to the circuit I posted.
Unity Gain is Gain=1=Av.
Since your Av is Av=Rb/Ra, make Rb=Ra, then Av=1 and you meet the unity gain definition of Gain=1=Av.
What does s stand for in the equation?
s=jw
From wiki:
"The transfer function can also be shown using the Fourier transform which is only a special case of the bilateral Laplace transform for the case where s = j\(\omega\)."
http://en.wikipedia.org/wiki/Transfer_function
If you don't know what s and unity gain are, how is it that you have a problem regarding transfer functions? The transfer function of a multi-pole filter is pretty advanced math, requiring an understanding of several layers of underlying concepts including complex algebra (imaginary numbers). I'm not criticizing you, just observing that you might be out of your depth.
ak
ak
Do you just write the transfer function in terms of the variables since they don't have any values given in the question or am I missing something?
No, you are not missing anything. For Part a you just write transfer function in terms of R1, R2, C1, C2, Ra, Rb. That is exactly what Part a asks you to do.
Yes, for example
(Vs - Va)/R1 = (Va - Vp)/R2 + (Va - Vout)*s*C1
(Va - Vp)/R2 = Va*s*C2
Vout = Vp * Av
Where Av = 1 + Rb/Ra
And you solve this for Vout/Vs
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The design given on the wikipedia article does not have Ra and Rb, would you happen to have an example similar to my design circuit
Found this example:
http://www.daycounter.com/Filters/SallenKeyLP/Sallen-Key-LP-Filter-Design-Equations.phtml
How would you factor in the Rb and Ra into that equation, which isn't in the example circuit but in my question
