buddypoor^^ Thank you very much.
I would like to discuss with u more, since i am not totally get your idea
a . In general, OTA-C structures are appropriate for tunable filters,however, an upper limit of about 900 MHz seems to be problematic. Monolithic integration is necessary.
Question : I am not clear about "Monolithic integration is necessary". I read some papers, people can design the filter up to GHz with gm-c filter. i would like to know your meaning, thank you!
2) How to decide the bandwidth and gain of OTA ? I have no idea
OTA has no "gain", but a transconductance instead. Frequency range could be a problem.
Question: OTA has Iout/Vin (transconductance). But when we design OTA for OTA-C filter, how can we set the specification for OTA? And what's the relationship of OTA's bandwidth and bandpass filter's bandwidth?
3) The linearity of OTA also should be improved. By using source degeneration... I still can not get good linearity
What means "good" ? What are your requirements regarding dynamic range and input/output levels ?
Question: "Good" means i would like to get IIP3=15dBm for OTA-C filte. But now i only get -9dBm. so i modify the OTA, add source degeneration. but still can not get 15dBm IIP3
4) Do you think it is possible design one filter with this range tuning ability?
No, I donīt think so. More than that, a tunable BP structure with a constant bandwidth (instead of constant Q) is hard to design. So, it looks not too good for your task.
Question: I would like to know what's the reason you feel one filter is impossible to cover whole frequency range? based on analysis or ..
5) I would like to build the 4th order biquad OTA-C filter, but i don't know the exact steps to build OTA-C filter. It is not like
active-RC, we can use "filter solution" to get coefficient...I am really confuse and not clear
sorry to ask so many questions
sincerely yours
yixiusky