Modulation

Abstract

An important use of PLLs is in the phase or frequency modulation of a stable carrier wave or, conversely, in the demodulation of phase or frequency modulated signals. PLLs are attractive in modulator applications due to the combination of controllable modulation with a highly stable and adjustable carrier frequency; they are also attractive in certain demodulator applications because of their superior performance at low S/N ratios. The basic arrangement of a PLL modulator is shown in figure 4.1. Angle modulation is easily implemented by adding a modulating signal either before the loop filter for phase modulation or after the loop filter for frequency modulation.