Modulation and Modulators
Modulation is the process that allows the information content of an audio, video, or data signal to be transferred to a region of higher frequencies where the transmission can be effective. In this case, the spectrum bandwidth of the modulating signal must be much smaller compared to the carrier frequency being modulated. During the modulation process, one or several parameters of the carrier signal such as amplitude, frequency, or phase vary according to the modulating signal when the modulator changes the signal into a form suitable for transmission over the proper radio channel. More complex modulation process includes digitization and encoding of the modulating signals. Depending on the communication systems with corresponding requirements on transmitting power, signal quality, frequency bandwidth, power consumption, system complexity, or cost, different types of the modulation scheme can be used based on analog and digital modulation techniques.
This chapter discusses the basic features of different types of analog modulation including amplitude, single-sideband, frequency, and phase modulation and basic types of digital modulation such as amplitude shift keying, frequency shift keying, phase shift keying, or pulse code modulation and their variations. The principle of operations and various schematics of the modulators for different modulation schemes including Class-S modulator for pulse-width modulation are described. Finally, the concept of ...