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Time Recovery Circuit With Two Speed Phase Correction

IP.com Disclosure Number: IPCOM000073867D
Original Publication Date: 1971-Feb-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 3 page(s) / 53K

Publishing Venue

IBM

Related People

Liberman, RA: AUTHOR

Abstract

This circuit is directed to modulated carrier wave communication systems with control means including a local oscillator synchronization means. A pilot tone is transmitted with an information signal to provide a coarse phase correction to permit fast synchronization acquisition.

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Time Recovery Circuit With Two Speed Phase Correction

This circuit is directed to modulated carrier wave communication systems with control means including a local oscillator synchronization means. A pilot tone is transmitted with an information signal to provide a coarse phase correction to permit fast synchronization acquisition.

A timing window is constructed at the receiver from the pilot tone during which period the center of an "eye" occurs. The coarse-phase corrector examines the timing pulse at the receiver. If the timing pulse does not occur within the timing window constructed from the pilot, the coarse-phase corrector inserts a pulse in the pulse train output of the receiver's high-frequency oscillator after that high frequency has been partially reduced. By inserting the pulse after the frequency is partially reduced, rather than before any reduction in frequency, there is a large effect on the final phase of the fully reduced pulse train. This corrected pulse train forms the output of the coarse-phase corrector. This output is further reduced in frequency by a frequency divider and forms the timing pulses at the receiver. It has the same frequency as that of the received data. The fine-phase correction is performed by a threshold crossing detector and a fine-phase corrector operating on the unreduced high-frequency oscillator output. The threshold crossing detector compares the time at which the information signal crosses data levels with the receivers timing pulse.

The device shown in Fig. A operates simultaneously and continuously making coarse phase adjustments and fine phase adjustments. The fine phase adjustments are made by pulse adder or deleter 7 in combination with threshold crossing detector 1 when the timing pulses do not coincide with threshold crossings.

For example, referring also to Fig. B, threshold crossing detector 1 indicates a transition at pulse 201. Pulse 201 occurs after the receiver timing pulse has risen, i.e., the timing pulse is in an up state after having risen from a low state. Therefore, the receiver's timing...