The rst term will be blocked by the if lter and the

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Unformatted text preview: (ωLO = ωc + ωIF ). Since ωLO > ωc , the results for ωLO > ωRF are applicable in this case. If the signals are summed at the output of the mixer then according to equation 1 the output will be zero. If the signals are differenced, then according to equation 2 the output will be A cos[(2ωc + ωIF )t] + A cos(ωIF t). The first term will be blocked by the IF filter, and the second term will be passed. Thus, we should use the − sign in the combiner in order to produce the desired frequency conversion. d. The image signal is at ωRF = ωc + 2ωIF . For the image signal, ωLO < ωRF , so if the signals are summed the output will be A cos(ωIF t). If the signals are differenced the output is A cos[(2ωc + 3ωIF )t]. Thus, when the signals are differenced, as required to produce the required output when the desired signal is input to the mixer, the image signal produces a finite output from the mixer, but the frequency of the output signal will be much higher than ωIF . Hence the response due to the image signal is easily rejected by the IF filter, so the image signal will not produce any output after the IF filter. 4...
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