Phase-Locked Loops

This chapter begins with introduction of the basic phase-locked loop concept. Then, the basic performance and structures of the analog, charge-pump, and digital phase-locked loops are analyzed. The basic loop components such as phase detector, loop filter, frequency divider, and voltage-controlled oscillator are discussed, as well as loop dynamic parameters. The possibility and particular realizations of the phase modulation using phase-locked loops are presented. Finally, general classes of frequency synthesizer techniques such as direct analog synthesis, indirect synthesis, and direct digital synthesis are discussed. The proper choice of the synthesizer type is based on the number of frequencies, frequency spacing, frequency switching time, noise, spurious level, particular technology, and cost.


The basic phase-locked loop (PLL) concept has been well known and widely used since it was proposed and described by Appleton and later analyzed by Bellescize [1,2]. Starting with the rapid development of integrated circuits in the 1970s, the PLL had become an important part of modern communication systems, improving their performance and reliability. A PLL circuit responds to both the frequency and the phase of the input signal, automatically raising or lowering the frequency of a voltage-controlled oscillator until it is synchronized with the reference in both frequency and phase. In other words, the PLL controls the phase of its RF output ...

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