Browse Prior Art Database

Phase-Locked Loop

IP.com Disclosure Number: IPCOM000037208D
Original Publication Date: 1989-Nov-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 2 page(s) / 44K

Publishing Venue

IBM

Related People

Cutshaw, R: AUTHOR

Abstract

This article describes a method of frequency modulating (FM) a phase- locked loop and building a frequency agile FM or frequency shift keying (FSK) transmitter.

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Phase-Locked Loop

This article describes a method of frequency modulating (FM) a phase- locked loop and building a frequency agile FM or frequency shift keying (FSK) transmitter.

A conventional translation loop is shown in Fig. 1. The frequency modulated phase-locked loop disclosed herein is shown in Fig. 2. This loop is similar to the conventional one in Fig. 1 in that all of the parts are the same. The difference is in the location of the translation mixer and filter. If the modulation was presented to the mixer in the loop in Fig. 1, the modulation would be reduced in frequency deviation by the factor: Fdeviation/N. There also would be a problem in building a low-pass filter with frequency agility with a sharp cut off to do the low-pass filtering. Usually a band-pass filter is used after the mixer in a translation loop (see Fig. 1).

In the loop of Fig. 2, the filtering is done at lower frequency, after the mixing, but before the pass detector. The requirements on the filtering are eased and the need for frequency agility is eliminated. The frequency deviation is not reduced by Fdeviation/N. The frequencies are shown in Figs. 1 and 2. The loop of Fig. 2 is made frequency-agile by changing the number in the N divider[*].

(Image Omitted)

Reference: * W. F. Egan, Frequency Synthesis by Phase Lock, John Wiley & Sons, New York, NY (1981).

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