I need to design a sallen key filter such that the output of the filter is a pulsating DC or ripple output when compared to the input. I tried implementing the below circuit but the output is not satisfactory. I am getting a sine wave instead of a pulsating dc or a ripple.
Frequency at the input of the filter is 20Khz.
Note: The input of the filter is the result of multiplication of sine and square wave.
Blue wave form  input of filter
Green wave form  output of the filter
and the desired ripple output image is also posted below.
Desired output:
Frequency at the input of the filter is 20Khz.
Note: The input of the filter is the result of multiplication of sine and square wave.
Blue wave form  input of filter
Green wave form  output of the filter
and the desired ripple output image is also posted below.
Desired output:
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