Method and apparatus for synchronization of periodic signals

• US 6,191,821 B1
• Filed: 05/29/1998
• Issued: 02/20/2001
• Est. Priority Date: 05/30/1997
• Status: Expired due to Term

• Current Assignee: 0960471 B.C. Unlimited Liability Company, HB Canada Communications Ltd.
• Original Assignee: Leitch Technology Corporation (L3Harris Technologies, Inc.)
• Inventors: Kupnicki, Richard A.
• Primary Examiner(s): Kostak, Victor R.
• Application Number:
  US09/086,608
• Time in Patent Office: 998 Days
• Field of Search: 348/512, 348/500, 348/518, 348/510, 348/501, 348/722, 348/495, 375/354, 375/362, 375/365, 375/371, 375/373, 327/141, 327/142, 327/145, 327/151, 327/160, 327/161, 327/162, 327/163
• US Class Current: 348/512
• CPC Class Codes: H04N 5/04 Synchronising for television systems using pulse code modulation H04N7/56
• CPC Class Codes: H04N 5/06 Generation of synchronising signals
• CPC Class Codes: H04N 5/46 for receiving on more than one standard at will deflecting circuits of multi-standard receivers H04N3/27
• CPC Class Codes: H04N 9/45 Generation or recovery of colour sub-carriers

Abstract

A method and apparatus for synchronizing unrelated reference signals originating from two or more sources at different locations, which signals may be in different signal formats and/or subject to different delays at the receiving station. A master generator having an absolute time input from a highly stable time source generates a master reference signal having a frequency that is a common multiple of the frequencies of the unrelated reference signals. A counter is implemented from an arbitrary initial time point and the time elapsed from the initial time point to a synchronizing event is periodically encoded into the master reference signal as time code data. A slave generator associated with each information signal is genlocked to the master reference signal, and the time code data is encoded into the slave reference outputs. Each synchronizing event is thus associated with time code data specifying the absolute time of the synchronizing event, which can be inserted into an upstream position in the slave reference output associated with the information signal. Thus, two signals originating from different locations can be precisely synchronized so that transmission from one source to the other is synchronous and signal timings are known in advance.

Claims

1. A method of synchronizing a plurality of periodic signals in time, comprising the steps of

(a) defining an arbitrary point in time at which said signals are assumed to be exactly synchronized,

(b) implementing a counter to generate time code data representing time elapsed from said arbitrary point in time,

(c) encoding time code data, comprising the instantaneous value of said counter corresponding to the next defined synchronizing event into each one of said signals,

(d) calculating a delay constant for a first one of said signals at a later point in time by comparing the value of the time code data encoded in said first one of said signals to time code data encoded in a second one of said signals,

(e) delaying said first one of said signals by said delay constant calculated in stop (d).

2. The method of claim 1 wherein in step (c) the time code data is encoded within a frame mediately preceding the next defined synchronizing event.

3. An apparatus for synchronizing one or more unrelated reference signals in time, comprising

a master sync generator adapted to accept an absolute time reference as an input, compring a counter for counting elapsed time fron an initial time point and encoding a value representing said elapsed time into a master reference signal output by the master sync generator, and

at least one slave sync generator comprising

an input connected to said master reference signal,

a decoder connected to said input to decode time code data encoded in said master reference signal,

a counter connected to said decoder and synchronized to said time code data,

a generator for generating a slave reference signal comprising time code data comprising the instantaneous value of said counter at the next defined synchronizing event for said slave reference signal, and

an output connected to said generator.

4. The apparatus of claim 3 wherein the value representing said elapsed time encoded into the master reference signal represents a calculation of elapsed time to the next defined synchronizing event.

5. The apparatus of claim 4 wherein the value representing said elapsed time is encoded into the master reference signal within a frame immediately preceding the next defined synchronizing event.

6. A system for synchronizing one or more signals, comprising

(a) a master sync generator comprising

an input connected to an absolute time reference source,

a counter connected to said input and synchronized to said absolute time reference source,

a generator for generating a refernnce signal,

an encoder connected to said counter and said generator to encode time code data comprising the instantaneous value of said counter corresponding to the next defined synchronizing event into said reference signal to create a master reference signal, and

an output connected to said generator to output said master reference signal, said master sync generator being adapted to generate an output signal in which said time code data is encoded, and

(b) a slave synchronizing generator for receiving said master reference signal from said master sync generator, comprising software for decoding the encoded time code data to synchronize said one or more unrelated timing signals.

7. The system of claim 6 wherein the time code data is encoded within a frame immediately preceding the next defined synchronizing event.