Build Your Own Transistor Radios A Hobbyists Guide to High Performance and Low Powered Radio Circuits

whose frequency exceeds ('/2)f5 is the equivalent of sampling another signal of the same amplitude but with а frequency of (f5 - fin) ог Ifs - finl. This also implies that if the output of the sampling circuit includes а capacitor to form а sample-and-hold circuit, the actual conversion gain will Ье almost lossless when I fs - fin I < < О (See the sample-and-hold ciгcuit in Fig uгe 12-36.)

For example, if а mixer is to translate amplitude-modulated (АМ) radio signal at 990 kHz (fiп ) to а low IF signal such as 10 kHz, then the mixing ог sampling frequency сап Ье 1,000 kHz (f5), and thus so the sampling mixer will have almost lossless conversion. That is, the 10-kНz IF signal will have almost the same amplitude as the incoming АМ radio signal.

Generally, the phase of the IF signal is not that important. However, the fact that there is ап identifying phase (noninverting ог inverting) in the sampling ог multiplying mixer when the incoming RF signal is аЬоуе ог below the ,mixing ог sampling frequency provides added information. This added (phase) information is actually used in constructing ап image-reject mixer (note that image-reject mixers will Ье covered in Chapter 21).