Chapter 8 - Phase-Locked Loop Techniques in Modern Communications Systems

Abstract

In modern receivers for wireless applications, channels are selected by mixing an incoming RF signal with a local oscillator signal. One popular and affordable method of tuning is employing a frequency synthesizer based on a phase-locked loop (PLL). Because coherent systems have higher noise immunity than non-coherent systems, coherent systems are highly preferred in modern wireless communication systems. In order to eliminate the static phase error, it is desirable to make the system have additional pole at the origin. This type of system is a type-II system as there are two poles at the origin. A PLL has various frequency ranges to specify its tracking/acquisition performance lock-range, pull-in range, and hold-range. When the reference signal is leading the feedback signal, the output will produce more positive area and thus a higher level of control voltage. The phase detection range of phase detectors depends on the devices used. A PLL forces the divided frequency to be exactly equal to the frequency of the input signal in the lock mode. This chapter highlights that the most critical specification for any oscillator is its spectral purity.