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Design >> RF Design >> CMOS mixer noise
https://designers-guide.org/forum/YaBB.pl?num=1266507572

Message started by solanojedi on Feb 18^th, 2010, 7:39am

Title: CMOS mixer noise
Post by solanojedi on Feb 18^th, 2010, 7:39am

Hi everybody,
I have some doubts about the problem of noise in cmos mixers (single balanced mixer http://upload.wikimedia.org/wikipedia/commons/thumb/9/97/Single_Balanced_Mixer_in_Integrated_Circuit.svg/200px-Single_Balanced_Mixer_in_Integrated_Circuit.svg.png ).. where does it come from (flicker, thermal...?)? And which is the more critical? How does it "move" in the frequency domain after the downconversion?
Thank you in advance!

Nicola

Title: Re: CMOS mixer noise
Post by pancho_hideboo on Feb 18^th, 2010, 8:25am

solanojedi wrote on Feb 18^th, 2010, 7:39am:

where does it come from (flicker, thermal...?)? And which is the more critical?

It depends on IF frequency and LO signal driver circuits.

solanojedi wrote on Feb 18^th, 2010, 7:39am:

How does it "move" in the frequency domain after the downconversion?

I can't understand what you want to mean.

Title: Re: CMOS mixer noise
Post by solanojedi on Feb 18^th, 2010, 8:36am

Maybe it's better reformulate all the questions in "the noise contribution in a single balanced mixer output, seen in the frequency domain".
Thank you!

Title: Re: CMOS mixer noise
Post by pancho_hideboo on Feb 18^th, 2010, 8:40am

solanojedi wrote on Feb 18^th, 2010, 8:36am:

"the noise contribution in a single balanced mixer output, seen in the frequency domain".

Again, it depends on IF frequency and LO signal driver circuits.

Title: Re: CMOS mixer noise
Post by solanojedi on Feb 18^th, 2010, 8:56am

Ok, but in this architecture http://upload.wikimedia.org/wikipedia/commons/thumb/9/97/Single_Balanced_Mixer_in_Integrated_Circuit.svg/200px-Single_Balanced_Mixer_in_Integrated_Circuit.svg.png what happen with the noise? The switching couple, ideally, doesn't contributes to the output noise, isn't it? Thanks!

Title: Re: CMOS mixer noise
Post by pancho_hideboo on Feb 18^th, 2010, 9:07am

solanojedi wrote on Feb 18^th, 2010, 8:56am:

The switching couple, ideally, doesn't contributes to the output noise, isn't it?

Strictly speaking, it is not correct.
Many people think if we minimize time period when switching MOS pairs are on state at same time, we can minimize noise from RF MOS.

Again(this is third times), it depends on IF frequency and LO signal driver circuits.

Also see http://www.designers-guide.org/Forum/YaBB.pl?num=1162399761
There are much direct feed through from RF to IF output and LO to IF in SBM(Single Balanced Mixer).

Title: Re: CMOS mixer noise
Post by solanojedi on Feb 18^th, 2010, 9:25am

Ok..! Thanks a lot!

Nicola

Title: Re: CMOS mixer noise
Post by RFICDUDE on Feb 26^th, 2010, 3:21am

One other note, the circuit shown is not strictly correct either. There is no need to have an "ideal" current source biasing the circuit. As shown the current source will degenerate all the gain of the common source input stage and the NF will be infinite.

Seems like a petty detail, but you will never get through a job interview on mixers if you imply there is a current source biasing the common source stage (at least if you do not provide by passing).