Browse Prior Art Database

Communications Receive Clock Synchronization

IP.com Disclosure Number: IPCOM000084014D
Original Publication Date: 1975-Sep-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 3 page(s) / 42K

Publishing Venue

IBM

Related People

Leikam, GE: AUTHOR

Abstract

A business machine clock is provided to supply transmit and receive timing signals used for synchronous communications when nonsynchronous modems are employed. The receive clock signals must, of necessity, be derived from the timing information inherent in the received data transitions, in order to achieve and maintain bit synchronization with the remote transmitter.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 53% of the total text.

Page 1 of 3

Communications Receive Clock Synchronization

A business machine clock is provided to supply transmit and receive timing signals used for synchronous communications when nonsynchronous modems are employed. The receive clock signals must, of necessity, be derived from the timing information inherent in the received data transitions, in order to achieve and maintain bit synchronization with the remote transmitter.

Waveform 1 shows data having alternate 1's and 0's at successive bit times. The negative-going transitions of receive clock (RC) waveform 2 are the points at which waveform 1 is sampled. Ideally, the phase of waveform 2 is adjusted so that the negative-going transitions of waveform 2 occur at center points 11, 12, 13, 14, etc., of the bit times of waveform 1.

Due to a communications disturbance, the negative-going transitions of RC waveform 3 are not in phase with the center points of the bit times of waveform 1 and a correction of the phase of waveform 3 is, therefore, desirable. The period of the waveform 3 is equal to the nominal bit times of waveform 1.

Assuming that the periods of the RC waveforms begin at each positive-going transition of the RC waveforms, a data transition is defined as a late transition if it occurs during the first half of an RC waveform period, as is the case with data waveform 1 with respect to RC waveform 3. Conversely, a data transition is defined as an early transition if it occurs during the second half of an RC waveform period.

To synchronize the late transitions of waveform 1 with RC waveform 3, the simplest and most common correction scheme consists of delaying waveform 3 by one correction increment, Delta T, for each late transition until synchronization is achieved. If any early transitions are

To synchronize the late transitions of waveform 1 with RC waveform 3, the simplest and most common correction scheme consists of delaying waveform 3 by one correction increment, Delta T, for each late transition until synchronization is achieved. If any early transitions are detected waveform 3 is advanced by Delta T.

A considerable amount of bias distortion is present in data waveform 5 to effec...