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Sallen and Key Bandpass filter

cps13

Feb 25, 2013
54
Joined
Feb 25, 2013
Messages
54
Hi,

I have the following question, which I need some fundamental help with to get going:

Design and PSPICE model a bandpass filter of ‘Sallen and Key’ topology and having the following characteristics: fo ~ 3.3kHz, Q ~2.2. Verify your design by means of a Bode plot.

From my learning material, and what I can find online. There appears to be a specific circuit for a Sallen & Key bandpass filter.

My questions are:

1) Should I be cascading a low-pass and a high-pass filter still to create the 'band' for the desired circuit? Everything online and in my material doesn't suggest so, but I thought fundamentally this is what a band pass filter is?

2) The question specifies fo as 3.3kHz. I understand this is the output frequency, but I don't understand how this relates to a bandpass filter? Is 3.3kHz on my bode plot where I should see -3dB (0.707) on my slope?

3) I know the fo value and the Q ratio from the question. However, i'm not sure how to get started to find my RC values.

Thanks,
 

crutschow

May 7, 2021
469
Joined
May 7, 2021
Messages
469
fo is the center frequency where the gain is nominally 0dB (1) for an op amp configured as a gain-of-one follower.
You can do the filter with one op amp, as shown here.
 
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