R/C bandpass filter with unity buffer..

I need a simple bandpass filter (6db) with switched capacitors...

this is how I would do it...



what do you think about it...

is there a way to omit the first or second buffer stage?

mat

You can't omit the first stage unless you always know you will be driving it from a zero-Ohm source, but you can condense the high and low pass sections into one Sallen-Key bandpass filter.

See, for example: http://www.technick.net/public/code/cp_dpage.php?aiocp_dp=cir_filter_bp2ni_sk_01

Note that if you condense into one stage, the high and low pass cut-off frequencies interact and may not be switchable independently.

I'm hoping that by "switched capacitors" you mean physical capacitors selected by a rotary switch and not a switched-capacitor filter integrated circuit.

You shouldn't need the output coupling capacitor if you are using split power rails. If you're not, then you need an input capacitor as well, and the ground points have to be a half-rail point in d.c. terms.

thank you!

the reason is that I want to use a rotary switch with 2x6 positions and it should switch the cap for two channels..

the sallen key filter is a second order filter and I would have to switch between 2 caps/channel