Hi all,

i have a question about channel select filter (CSF) design... My thinking is that the 2 main requirements are

1)  attenuate interference so that IIP3 of following blocks does not need to be good

2)  attenuate out-of-band noise including interference (considered random)

So the thing is the CSF center frequency (f0) can change by around 10% for example. This can lead to an attenuation of the desired signal. However, my CSF is only 3rd or 4th order, and most likely the signal will only be attenuated by 3 dB at the very most (due to the frequency offset). Requirements 1 and 2 will still be met with a 10% deviation in f0. Furthermore, this 3 dB loss doesn't seem to have much affect on the system NF since the CSF is near the end of the RX chain. So is it fair to say that i can live with the 10 %variation in f0?

thanks in advance,

Aaron

well...10% is a bit of a guess...I used resistive degeneration to get high IIP3 and designed it so that the passband gain and center frequency would be "immune" to resistor variation since R variation seems to be higher than C variation. Also, the overall biasing is referenced from a bandgap so i don't expect the current to change much. The manufacturers quote a 10% variation in C so that's what i based my estimation on.

Do you think I can get away with that or should I go for  a tuning loop? I was told that it wouldn't be necessary but i always had doubts. Just looking for an outside opinion

Not so familiar with ISI...better start reading again...

thanks,
Aaron