hello....

I was asked to design a 3rd order lowpass filter with a cutoff frequency of 6Khz.

I was not able to figure out a continous time circuit for the cascading.can u guys please help in designing a butterworth 3rd order lowpass filter.

 

I always cheat.

http://www.daycounter.com/Filters/LC-Butterworth-Filter/LC-Butterworth-Filter-Calculator.phtml

 

For 6kHz, an active-filter would be simpler. Here's how to make a single op amp 3rd order filter.

 

I find this application very useful for this kind of task:

http://www.ti.com/tool/filterpro

and it's very reasonably priced (free! )