Circuit and method of digital carrier detection for burst mode communication ...

United States Patent m

Wilson

[54] CIRCUIT AND METHOD OF DIGITAL

CARRIER DETECTION FOR BURST MODE
COMMUNICATION SYSTEMS

[75] Inventor: William B. Wilson, Shillington, Pa.

[73] Assignee: AT&T Bell Laboratories, Murray Hill, N.J.

[21] Appl. No.: 515,293

[22] Filed: Apr. 27,1990

[51] Int. CI.' H04B 1/10

[52] U.S. CI 375/104; 455/223;

328/109

[58] Field of Search 375/104, 102, 94, 5;

455/222, 223, 224, 303, 312, 218; 328/109, 110;

329/318, 341, 349, 313

[56] References Cited

U.S. PATENT DOCUMENTS

3,437,937 4/1969 Warfield 455/221

3,633,112 1/1972 Anderson 455/221 X

3,852,671 12/1974 Risley 455/222 X

3,873,925 3/1975 Eastmond 455/221

3,902,123 8/1975 Oomen 455/221

3,939,425 2/1976 Toyoshima 455/222

3,939,431 2/1976 Cohlman 375/5

4,344,175 8/1982 Leslie 375/94

4,445,092 4/1984 Yoshinaka et al 455/223

4,458,204 7/1984 Dellande et al 375/104 X

4,630,290 12/1986 Kage 375/104

[ii] Patent Number: 5,199,049 [45] Date of Patent: Mar. 30,1993

4,815,108 3/1989 Oda 375/102

OTHER PUBLICATIONS

"Draft Supplement to IEEE Std 802.3, CSMA/CD Access Method and Physical Layer Specifications", IEEE Std. 802.3, Type 10BASE-T Pat Thaler, Feb. 15, 1990 pp. 1-29.

"DP83922 Twisted Pair Transceiver Interface (TPI)",
National Semiconductor, Dec. 1989, pp. 1-15.

Primary Examiner—Curtis Kuntz
Assistant Examiner—Tesfaldet Bocure
Attorney, Agent, or Firm—Scott W. McLellan

[57] ABSTRACT

A digital squelch circuit for detecting valid data signals in a burst mode communication system, such as a packet-based local area network. Transitions in the input signal to the squelch circuit start a counter which asserts at least one signal a predetermined time from the transition. The absence or presence of the signal when the next transition in the input signal occurs determines if the frequency of the input signal is less than or greater than a frequency related to the predetermined time interval. When a predetermined number of transitions meeting the desired frequency requirement are received, the input signal is judged valid.

14 Claims, 5 Drawing Sheets