Overview

This chapter presents PLL applications and extensions. PLLs are used to generate frequencies, recover a clock from a signal, resynchronize signals, and help convert signals to a digital representation. First, PLLs synthesize frequencies to be used in computers (microprocessors and DSPs), test instruments, land-based communications (cell phones), space-based communications, radar, and electronic-warfare systems. The wide variety of applications with different requirements leads to different synthesizer configurations. We will study the various configurations to help in selecting the best one.

In clock recovery, many systems transmit or receive data without any additional timing reference. To an ever-increasing extent, communication links use digital formats to transmit information synchronously in a continuous uniform pulse stream. We will study clock-recovery techniques because every digital communication link uses a PLL in the reception of this information.

Communication systems, radar systems, data-acquisition systems, and test equipment convert analog signals to digital words for digital processing. Digital processing assumes equally spaced time samples; however, actual samples from analog-to-digital (A/D) converters have slightly unequal time spacing. Phase noise from the oscillator that generates the sampling clock produces this change in time spacing. In digital processing, equally spaced time samples are critical to system performance. The phase noise of the sampling clock affects the dynamic range of the A/D converter by adding noise. We will study the limitations of the conversion process so that adjustments can be made to PLL designs to overcome these limits.

As digital processes reduce the cost of circuit functions and design tools to...