aaron_do wrote on Jul 13th, 2010, 2:03am:you mentioned tuning to the -6 dB frequency. I think you may have misread the post since this is a bandpass filter. Otherwise could you please explain a bit further. Thanks.
Ok, my bad, I was thinking a LPF.
For a BPF its a little different.
If the BPF is narrow in BW you tune for an amplitude peak using a band centered reference signal.
If the BPF is a bit wider, you generate two reference signals that sit on band edges (one above band center, one below), and you adjust your tune for amplitude balance between the two signals.
Another option is using a band centered test signal and adjusting the tuning up-down and find the -6dB points of the
tuning system, and then splitting the difference to center the BPF. Tuning system has to be linear.
Many possible options there.
The reason I suggested -6dB is because it's easily generated, V/2 is pretty easy to do right?
gmC filters will require updating due to temps and process corners. Will need to update settings periodically.
Oh, and I am a big proponent of digital tuning systems. Switched systems are just a bit more predictable than an analog FB system.