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Measurements >> Phase Noise and Jitter Measurements >> Noise figure for receiver with IQ outputs?
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Message started by weber8722 on Dec 2^nd, 2011, 5:35am

Title: Noise figure for receiver with IQ outputs?
Post by weber8722 on Dec 2^nd, 2011, 5:35am

Hi

I wonder on how to treat noise in an IQ mixer? There we have 2 outputs, but in all noise-figure testbenches I have seen people are just probing only one of them. Also allmost all tools only offer one output port for probing. Is this really correct?

For a similar case like probing not a full differential signal but only the voltage to gnd the results will be definately wrong due to common-mode noise (which might be quite large), and the real noise depends on the CMRR of the next stage. I wonder if there are similar effects in IQ outputs? Or do they not matter due to 90° phase shift, thus we add noise via sqrt(x²+y²) and signals too. However, this is only correct if there are no phase errors and no correlations. Is there a kind of ideal wide-band IQ combiner?

Bye Stephan