Complete Wireless Design
If you want to climb the learning curve with grace, and start designing what you need immediately, this easy-to-understand guide will help you design an entire radio system from the ground up.
TABLE OF CONTENTS Complete Wireless Design
Chapter 5: Frequency Synthesizer Design
A method of combining the wide tunability of LC oscillators with the high frequency stability of crystal oscillators is a necessity in modern wireless communications design. We find both of these abilities in frequency synthesis, which is a method of generating a multitude of exceptionally accurate frequencies from a single, low-frequency crystal oscillator. It is the dominant technique for variable-frequency production in most receivers, transmitters, transceivers, and test equipment today.
By far the most widespread method of frequency synthesis is implemented by the phase-locked loop (PLL); but a newer technique, referred to as direct digital synthesis [DDS; sometimes called a numerically controlled oscillator (NCO)], is becoming increasingly prevalent in certain applications. We will concentrate on the PLL, which is easier to design, more versatile, and much higher in frequency.
5.1 Phase-Locked Loops
5.1.1 Introduction
The majority of frequency synthesis is derived from the phase-locked loop. Figure 5.1 demonstrates all of the vital circuits that make up a common single-loop PLL synthesizer: A low-frequency crystal oscillator feeds a reference frequency into the R divider, which decreases the reference frequency to equal the desired f COM out of the N adjustable frequency divider, with the R divider allowing for different channel spacings. The reference frequency out of the R divider is then inserted into the phase comparator, which compares the phase of the R divider to that of the N adjustable frequency divider. The adjustable N frequency divider receives its own...
Copyright The McGraw-Hill Companies, Inc. 2001 under license agreement with Books24x7
