3.1. Superheterodyne Architecture

This is the most popular architecture used in communication transceivers. It is based on the heterodyne process of mixing an incoming signal with an offset frequency local oscillator ( LO) in a nonlinear device to generate an intermediate frequency (IF) signal in the receiver or to produce an RF signal from its IF version in the transmitter. The nonlinear device executing the heterodyne process is called a frequency mixer or frequency converter. In a superheterodyne transceiver, the frequency translation processes may be performed more than once, and thus it may have multiple intermediate frequencies and multiple IF blocks.

It is apparent that the same IF can be generated by an incoming signal with a frequency either above or below the LO frequency. Between these two frequencies, the one corresponding to the undesired signal is referred to as an image frequency, and the signal with this frequency is called as an image. The frequency difference between the desired signal and its image is twice the IF. To prevent the possible image interfering with the desired signal and other strong unwanted signals jamming the superheterodyne receiver, sufficient filtering before the frequency converter is usually needed. The bandwidth of this preselection filter is quite broad, and it usually covers the overall reception frequency band in a wireless mobile transceiver. The channel filtering of a superheterodyne receiver is performed in the IF blocks by means of passive filters with high selectivity. The reception channel tuning is often...