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Noise figure for receiver with IQ outputs? (Read 2341 times)
weber8722
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Noise figure for receiver with IQ outputs?
Dec 02nd, 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
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