Frequency Shifting

Abstract

In this chapter, we focus on the mathematical operation of “frequency shifting” that is fundamental to wireless communication systems. Frequency shifting (or “frequency translation”) is complementary to the frequency tuning mechanism used in VCOs. However, as will be shown, it is a much broader concept with a much wider range of applications. As it turns out, mathematical multiplication of two sinusoidal waveforms with given frequencies results in waveforms that contain both higher and lower frequencies. This phenomenon is known as “frequency shifting”, where the term “up-conversion” refers to the process of shifting of lower frequency tone to the upper frequency range (used in RF transmitters), while “down-conversion” refers to the frequency shifting from higher to lower frequency ranges (used in RF receivers). Hence, in a complete wireless communication system, the information-carrying signal is shifted in both directions.