Adjustable Active Filter

Thread Starter


Joined Dec 19, 2006
Hi, Have a second-order Sallen-Key low-pass Butterworth Filter. Cutoff frequency must be adjusted: 10Hz, 100Hz, 1000Hz. The reasonable way for me is to use switching capicitors and resistors- will be there any problems if switching will be done with Analog Switch(like MAX333 etc) in contrast to simple toggle/rotary switches?

Ron H

Joined Apr 14, 2005
I would make 3 separate filters, with a 3 pole, single-throw switch (analog or rotary), followed, if necessary, by a voltage follower. This gets around any potential problems with switch resistance and capacitance. You use fewer switches and more op amps.