Frequency Transposition

Summary

Frequency transposition is carried out using a mixer circuit. There are two types of frequency transposition: (i) From lower to higher frequencies, also referred to as upconversion. The mixer is then an up‐converter; (ii) From higher to lower frequencies or referred to as downconversion. The mixer is, in this case, a down‐converter. This chapter briefly describes the operating principles, mixer characteristics, simple mixer operation, balanced mixer topologies, topology of passive and active mixers, and frequency multipliers. Down‐converter mixers help transpose the frequency of the desired input signal to a lower, so‐called intermediate frequency, allowing for easier signal processing. Up‐converter mixers transpose the intermediate frequency of the desired input signal to a higher frequency, also called the carrier frequency, which enables the signal to propagate. As multiplication is necessary for the proper functioning of an ideal mixer, we must use a nonlinear element to give an approximate product of the input signals.