Re: LO Phase Noise and wideband front ends

Christopher Bartram <cbartram@...>

I haven't seen the original post on this , but, I suspect that the problem isn't Phase Noise. For far too many people phase noise is a pretty diffuse concept, and it gets blamed for a lot of effects for which it's not responsible!

Phase noise is, in effect, a form of wideband frequency modulation, and falls away quite quickly at 20dB/octave as you move away from the carrier. What I believe, from reading Andy's post is that the problem is amplitude domain noise (AM noise) caused by eg. amplifiers in the signal path. This can have a pretty flat frequency/amplitude characteristic.

'Phase noise' gets the blame for many effects which are caused by AM noise, and is a particular nuisance in wideband systems, but it behaves differently to AM noise. Phase noise won't be cancelled in a balanced mixer, but AM noise will be.



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