DIGITAL PHASE COMPARATOR WITH IMPROVED SENSITIVITY FOR SMALL PHASE DIFFERENCES
 Inventor: Donald R. Preslar, Plainfield, N.J.
 Assignee: RCA Corporation, New York, N.Y.
 Appl. No.: 144,053
 Filed: Apr. 28, 1980
 Int. CI.3 H03D 13/00
 U.S. CI 307/528; 328/133
 Field of Search 328/133, 134; 307/272,
307/445, 514, 516, 525, 526, 527, 528
 References Cited
U.S. PATENT DOCUMENTS
3,610,954 10/1971 Treadway 307/528
3,710,140 1/1973 Volmerange .
3,714,463 1/1973 Laune .
4,023,116 5/1977- Alfke et al. .
4,122,405 10/1978 Tietz et al 328/133
4,278,903 7/1981 Ichinose .
FOREIGN PATENT DOCUMENTS
1256164 12/1971 United Kingdom .
1328031 8/1973 United Kingdom .
"A New Design Technique for Digital PLL Synthesizers", by Eric Breeze, Published in IEEE Transactions on Consumer Electronics, vol. CE-24, No. 1, Feb. 1978.
"Test Your Charge Pump Phase Detectors", by William Egan, Published in Electronic Design, Jun. 7, 1978. Technical Information on Integrated Circuit Types 11 COO Series, Published by Fairchild Semiconductor Group, Fairchild Camera and Instrument Corporation, 1978.
Integrated Circuit Application Note ICAN-6101, Published by RCA Corporation, 1978.
Primary Examiner—Alfred E. Smith
Assistant Examiner—T. N. Grigsby
■Attorney, Agent, or Firm—E. M. Whitacre; P. J.
Rasmussen; A. L. Limberg
A digital phase comparator for essentially eliminating the dead zone in the phase correction means of a phase locked loop. The digital phase comparator is arranged to provide respective up and down output pulses to operate respective charge pumps. The up and down output pulses at all times are greater than a predetermined time duration no matter how small the phase difference between comparator input signals. A delay means is provided in the phase comparator logic, which delay means substantially determines such predetermined time duration. The minimum pulse duration of the up and down signals is selected to be at least of a duration sufficient to operate its respective charge pump, thereby overcoming the finite turn on time of the respective charge pump, no matter how small the phase error.
9 Claims, 6 Drawing Figures