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Measurements >> RF Measurements >> Mixer Noise Figure Measurement
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Message started by Rehan Zakai on Mar 18^th, 2004, 5:50pm

Title: Mixer Noise Figure Measurement
Post by Rehan Zakai on Mar 18^th, 2004, 5:50pm

Can someone confirm that the actual noise figure measurements of a downconversion mixer using the Y-factor method or power gain method are single-side-band figures. I am following the assumption that all NF measurements involving a mixer are SSB. DSB nosie figure I believe is a 3dB improvement of the SSB NF by increasing the signal power.
Am I correct?
Rehan Zakai

Title: Re: Mixer Noise Figure Measurement
Post by mgehring on May 13^th, 2004, 12:27pm

Yes - the DSB figure implies that you have signals on both sidebands that will add in-phase after downconversion. The noise from both sidebands adds 3dB more than SSB ( assuming no image rejection ), and the signals add in phase to 6dB more signal than SSB, so the S/N is improved 3dB over SSB.

Personally, I don't know why anyone bothers with DSB NF, except to make their circuit look better. In most cases, it is a useless or misleading number.

Title: Re: Mixer Noise Figure Measurement
Post by RC on Dec 29^th, 2005, 9:06am

if the modulated signal is DSB, it does matter. it is definitely not a useless number.

Title: Re: Mixer Noise Figure Measurement
Post by cybq on Jun 8^th, 2006, 5:11am

I think SSB NF is the most case used item for evaluating the mixer noise performance, because there exist a image rejection filter before the mixer in down-converter.

But the DSB NF would be used in nowadays ZIF( direct conversion) receiver system, because the both sides of signal will be converted into the base band.

So, when simulating the NF of mixer, you must tell the simulator how to calculate the noise, where is it from.

(I'm system designer, not very familar with circuit design enviroment)

Title: Re: Mixer Noise Figure Measurement
Post by sgong2006 on Jul 11^th, 2007, 12:07am

I input thermal noise to the test unit, measure the output noise level, and estimate NF = Noise_output - Noise_input - Gain.
If the test unit is IF mixer, then the above calculated NF is SSB NF, which represent the true NF of that IF mixer;
If the test unit is direct conversion receiver (ZIF), then the above calculated NF is DSB NF, which represent the true NF of that Direct conversion Receiver.

Can anyone confirm about the above statement? Thanks.