Does anyone here know how various high-integration tuners achieve
more-or-less continuously-variable corner low-pass frequency on the baseband
outputs?
I'm aware of switched-capacitor filters, but my understanding is that
due to the high branch ratios, you need a clock with a very high ratio
relative to the corner frequency (like 50:1 or 100:1), and so doing
these for RF/IF filters isn't that practical.
Another approach is to have a little matrix of Ls and Cs and Rs, and
switch different ones in to get a tailored response. But again, CMOS chips
aren't that good at producing Ls and Cs of significant value.
Inquiring minds want to know....
-Marcus
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