Chapter 17

Project 8: Phase-Locked Loop

 

17.1    Theory

THE phase-locked loop (PLL) is widely used in communications receiver systems. Since even the fundamental theory of phase-locked loops has been the topic of dozens of textbooks, we will only briefly discuss, then implement, a single PLL design: a discretized, second-order Costas loop [87,88]. The simplified block diagram of such a system is shown in Figure 17.1. In this figure, s[n] is the sampled input signal, m[n] is an estimate of the message signal, T is the sample period, and ωc is the carrier frequency.

The basic operation of the PLL is as follows. The incoming signal s[n] is processed through a filter that implements a Hilbert transforming (HT) operation to create ŝ[n]. Recall ...

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