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Design >> RF Design >> How to get back clean fc
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Message started by merican on Oct 15^th, 2006, 10:02pm

Title: How to get back clean fc
Post by merican on Oct 15^th, 2006, 10:02pm

Greetings,

I have a question here....Let say I am receiving modulated RF signal.....between the LNA and Mixer, is there any way or method that I can get back the unmodulated RF ( clean fc) ? Usually we want to retreive the modulation but in this case, I need the clean fc back. Appreciate if anybody can guide me on this.

Thanks,
merican

Title: Re: How to get back clean fc
Post by ACWWong on Oct 17^th, 2006, 10:17am

i don't think an "easy way" exists.

On the bench you can pass the signal into a extremely high Q filter (off chip SAW or Cavity resonator, or onchip MEMS or BAW etc.) to strip off the modulation....
Circuit wise you could perhaps recover the carrier frequency in a CDR (clock data recovery) which would require you to divide the rf signal frequency down, pass it into a pll with appropriate phase detector/bandwidth in a hopeful ? attempt to strip off the modulation, then vco will now oscillate at clean RF...

Title: Re: How to get back clean fc
Post by merican on Oct 19^th, 2006, 6:17am

HI ACWWong,
Thanks for the tips.....so it seems that no easy way for that. Anyway, for the purpose of discussion, can we use phase shifter to get the fc back? Or is it will cancel the RF signal itselh.

Regards,
merican

Title: Re: How to get back clean fc
Post by ACWWong on Oct 19^th, 2006, 6:54am

hmm... i don't think so ...
what is the modulation type ?
why do you want the fc anyway?