Hi All,
I've been looking at a lot of active filter design software and design formulas, and none seem to care too much about the input and output impedances that the filter will want to "see" when placed in a circuit. When designing *passive* filters, we would typically specify these impedance values as a matter of course (normally 50 ohms). Why don't active filter design programs even ask what the input and output impedances are that the filter will have to work with, nor state what it is after the circuit is synthesized? Does it even matter; or will the frequency response and gain just not be affected by most normal values? Or is it assumed that the active filter will be placed between certain impedance values? If not, then how can I tell what the "optimal" impedance values should be for an active filter? This has me baffled!
Thanks,
-Bill