Ken Kundert
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Consider a high-side down conversion mixer at the input of a receiver. For the sake of the example, assume that the LO frequency is 1GHz and the input frequency is 1.2GHz and the output frequency is 200MHz. Well, because the mixer responds nonlinearly with respect to the LO, it is not only input signals at 1.2GHz that get converted to 200MHz at the output. Any signal at the input at ±k×1GHz+200MHz will also be converted to the output at 200MHz. In this example k=1 represents the desired harmonic, k=-1 represents the image harmonic, and all k≠±1 are the other harmonics. In other words, noise at the output at 200MHz that comes from the input at 800MHz is Nsi and from the input at 1.8GHZ, 2.2GHz, 2.8GHz, 3.2GHz, etc is Nso.
-Ken
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