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:

 

A Sallen-Key is supposed to produce the output you are getting. It is NOT supposed to produce the output you want. To produce the output you want from a sinewave input you use a rectifier and a filter capacitor. I don't know any other way.

 

A Sallen-Key is supposed to produce the output you are getting. It is NOT supposed to produce the output you want. To produce the output you want from a sinewave input you use a rectifier and a filter capacitor. I don't know any other way.

Thank you for your reply. I wanted to make sure whether the output I am getting was wrong or not. So you mean to say that my output is perfectly right?
If i use a rectifier i need to use 2 inputs for the diodes. But i have just 1 input. how do i go about connecting them? should i ground the other input of the diode?

 

Use Google to find:

1. Full wave rectifier
2. Bridge rectifier

Either circuit will provide an AC signal with positive peaks only. Adding a capacitor to this output will provide the signal you seek.