fz2101
Junior Member
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Posts: 17
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Please correct me if I'm wrong, thanks!
From what I understand, homodyne does NOT require image rejection, and that is one of its biggest selling points.
It is true that interferer power at the image frequency can be much larger than the desired signal, however this is an issue with the linearity of the mixer or image rejection, not noise figure. Of course, in the grand scheme of things (dynamic range), we need to take care of both.
The quadrature mixer comment is important, although I don't think only homodyne needs quadrature, since heterodyne eventually has to be downconverted to 0Hz as well (so there is always that folding of negative frequency portion onto positive frequency portion, and vice versa). Since NF deals with signal to noise ratio, if we have two paths working in parallel (''I and ''Q''), and we finally find sqrt(I^2+Q^2), while the noise add in power (are the noise correlated?), then the NF should not change, right?
Thanks,
frank
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