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US5909468A
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Method and apparatus for encoding PCR data on a frequency reference carrier
Assignee: Cisco Technology Inc
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Filing: 1997-03-28
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Granted: 1999-06-01
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Expires: 2017-03-28
Abstract
Abstract The present invention provides a method and apparatus for providing program clock reference (PCR) data to various devices in a digital transmission system in a robust manner. According to the present invention, PCR data representative of a snapshot of the system clock is encoded only an existing frequency reference signal. The frequency reference signal is a signal to which all clock dependent components lock to ensure that the proper frequency lock is used. By encoding the frequency reference with PCR data, effectively using the frequency reference as a PCR carrier wave, the PCR is efficiently and robustly delivered to the various devices requiring this PCR data.
Inventors
- 👤 Steven F. Lawrence
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-08 05:34
CPC Classifications
H; H04; H04N; H04N21/00; H04N21/20; H04N21/23; H04N21/236; H04N21/2365; H04N21/242
Claims Analysis
Total Claims: 20
Claim 1
Independent Claim
85 words
A method of encoding a clock signal on a frequency reference carrier, comprising the steps of: generating a continuous periodic waveform having a frequency within the television bandwidth; interrupting the generation of the continuous periodic waveform; generating a frame marking signal; inserting said frame marking signal in said continuous periodic waveform; encoding a clock reference signal on said continuous periodic waveform following said frame marking signal; and transmitting said continuous periodic waveform encoded with said clock reference signal to a plurality of digital transmission devices.
Claim 2
Independent Claim
85 words
A method of encoding a clock signal on a frequency reference carrier, comprising the steps of: generating a continuous periodic waveform having a frequency within the television bandwidth; interrupting the generation of the continuous periodic waveform; generating a frame marking signal; inserting said frame marking signal in said continuous periodic waveform; encoding a clock reference signal on said continuous periodic waveform following said frame marking signal; and transmitting said continuous periodic waveform encoded with said clock reference signal to a plurality of digital transmission devices.
Claim 3
Dependent Claim
16 words
The method of claim 1, wherein said continuous periodic waveform has a frequency of 3.375 MHz.
Claim 4
Dependent Claim
16 words
The method of claim 2, wherein said clock reference signal comprises a program clock reference signal.
Claim 5
Dependent Claim
14 words
The method of claim 3, wherein said program clock reference signal comprises 42 bits.
Claim 6
Dependent Claim
37 words
The method of claim 3, wherein the step of encoding further comprises: extracting said program clock reference from a memory, wherein an address in said memory containing said program clock reference is derived in a state machine.
Claim 7
Independent Claim
94 words
An apparatus for encoding a frequency reference carrier with a program clock reference, comprising: a continuous periodic waveform generator for generating a frequency reference carrier; a program clock reference generator for generating a program clock reference, said program clock reference generator comprising a state machine for generating an address and a memory containing a plurality of program clock references, said address being generated by said state machine, indicating a specific one of said program clock references contained in said memory; and a combiner for combining said frequency reference carrier with said program clock reference.
Claim 8
Independent Claim
94 words
An apparatus for encoding a frequency reference carrier with a program clock reference, comprising: a continuous periodic waveform generator for generating a frequency reference carrier; a program clock reference generator for generating a program clock reference, said program clock reference generator comprising a state machine for generating an address and a memory containing a plurality of program clock references, said address being generated by said state machine, indicating a specific one of said program clock references contained in said memory; and a combiner for combining said frequency reference carrier with said program clock reference.
Claim 9
Dependent Claim
13 words
The apparatus of claim 6, wherein said memory comprises a programmable read-only memory.
Claim 10
Dependent Claim
20 words
The apparatus of claim 6, wherein said continuous periodic waveform generator generates a waveform having a frequency of 3.375 MHz.
Claim 11
Independent Claim
69 words
An apparatus for generating a frequency reference carrier encoded with program clock reference data, comprising: a program clock reference generator; a latch for receiving digital samples of said program clock reference data; a state machine operatively coupled to said latch; a memory operatively coupled to said latch and said state machine; and a digital to analog converter for converting a digital output of said memory to an analog signal.
Claim 12
Independent Claim
69 words
An apparatus for generating a frequency reference carrier encoded with program clock reference data, comprising: a program clock reference generator; a latch for receiving digital samples of said program clock reference data; a state machine operatively coupled to said latch; a memory operatively coupled to said latch and said state machine; and a digital to analog converter for converting a digital output of said memory to an analog signal.
Claim 13
Dependent Claim
19 words
The apparatus of claim 9, further comprising a filter connected to an output of said digital to analog converter.
Claim 14
Dependent Claim
12 words
The apparatus of claim 10, wherein said filter comprises a low-pass filter.
Claim 15
Dependent Claim
16 words
The apparatus of claim 9, wherein said state machine provides a clock signal to said latch.
Claim 16
Dependent Claim
12 words
The apparatus of claim 8, wherein said latch comprises a shift register.
Claim 17
Dependent Claim
16 words
The apparatus of claim 9, wherein said program clock reference generator is sampled at predetermined intervals.
Claim 18
Dependent Claim
13 words
The apparatus of claim 14, wherein said predetermined interval is approximately 20 msec.
Claim 19
Dependent Claim
18 words
The apparatus of claim 9, wherein said memory contains symbol data corresponding to said program clock reference data.
Claim 20
Dependent Claim
13 words
The apparatus of claim 16, wherein said memory comprises a programmable read-only memory.
References Cited (Backward Citations)
US5710977A
Cited
US5661758A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
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| 3.5 Years (Year 4) | 2002-05-31 | 2002-11-30 | 2003-06-01 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2006-05-31 | 2006-11-30 | 2007-06-01 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2010-05-31 | 2010-11-30 | 2011-06-01 | $7700.00 | Window Closed / Lapsed |