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Question on Nf of filter + mixer

Question asked by FCHASTEL on Aug 13, 2009
Latest reply on Aug 19, 2009 by rulonv
Dear all,

I have the following simulation result that I don't understand. I have an image rejection filter followed by a mixer. The filter has IL = 0.001dB and the mixer has G =10dB and NF = 1dB. The NF I expect for the resulting system is therefore around 1dB since 1) the filter has almost no losses 2) it rejects the noise at the image frequency. However what I get is 0.018dB! I must say that I'm not able to explain how the mixer's NF does not impact on the system's NF.

Thanks for your help
Best regards