Patent EP0247891A2 successfully refreshed from Google Patents.
EP0247891A2
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Phase locked loop system
Assignee: RCA Licensing Corp
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Filing: 1987-05-29
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Granted: —
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Expires: 2007-05-29
Abstract
Abstract A phase locked loop is provided, which may be used in digital systems having clock signal frequency instabilities. The PLL has an analog oscillator (342) the frequency of which is determined by an analog control signal. The oscillatory signal is digitised (344) and phase-compared (338) with a digital reference signal, the digital output of the phase comparator being converted (340) to an analog signal to provide the oscillator control signal. In an application of the invention to a digital television receiver having a line-locked clock, the phase locked loop (350) regenerates two quadrature phase related subcarrier signals (COS,SIN) that are used to synchronously demodulate the chrominance signal components (CB) of the composite video signals into two color information signals (I,Q). The analog voltage-controlled oscillator (342) of the phase locked loop (350) generates a signal that is independent of any frequency instability in the line-locked clock signal. The analog-to-digital converter (344) digitizes this signal to provide one of the subcarrier signals, from which is generated the quadrature subcarrier signal, for example from a read-only memory (348). The two color information signals (I,Q) are obtained by multiplying (332,334) the chrominance signals by the first and second subcarrier signals. The phase comparator (336) determines the phase of the vector sum of the two color information signals and compares this against a desired phase value to generate a phase difference signal. The phase difference signal is filtered (338) and applied to the digital-to-analog converter (340) whichprovides the frequency control signal for the analog oscillator (342). A tracking filter (346) may be inserted at the output port of the analog-to-digital converter (344) to allow its quantization resolution to be reduced without affecting the performance of the phase locked loop.
Inventors
- 👤 Alvin Reuben Balaban
- 👤 Walter Heinrich Demmer
- 👤 Chandrakant Bhailalbhai Patel
- 👤 Leopold Albert Harwood
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-29 04:39
CPC Classifications
H; H03; H03L; H03L7/00; H03L7/06; H03L7/08; H04; H04N; H04N9/00; H04N9/44; H04N9/45; H03L7/085; H03L7/087
Claims Analysis
Total Claims: 8
Claim 1
Independent Claim
183 words
In a digital signal processing system including a source (300) of clock signal (CK) which may exhibit frequency instabilities, a phase locked loop system (350) characterized by the combination of: an analog variable oscillator (342,343) which is responsive to an analog control signal for generating a variable frequency oscillatory signal; digitizing means including an analog-to-digital converter (344) coupled to said oscillator for generating a digital signal including N-bit digital samples representing said oscillatory signal at instants in time determined by said clock signal, where N is an integer greater than 1; phase comparison means (336) coupled to said analog-to-digital converter for generating a digital signal that is proportional to the difference in phase between the signal generated by said digitizing means and a reference signal; and digital-to-analog converting means (340), responsive to the digital signals generated by said phase comparison means, for generating said analog control signal, said analog control signal conditioning the variable oscillator to change the frequency of said oscillatory signal in a sense tending to cause the signals provided by said phase comparison means to converge to a predetermined value.
Claim 2
Dependent Claim
183 words
In a digital signal processing system including a source (300) of clock signal (CK) which may exhibit frequency instabilities, a phase locked loop system (350) characterized by the combination of: an analog variable oscillator (342,343) which is responsive to an analog control signal for generating a variable frequency oscillatory signal; digitizing means including an analog-to-digital converter (344) coupled to said oscillator for generating a digital signal including N-bit digital samples representing said oscillatory signal at instants in time determined by said clock signal, where N is an integer greater than 1; phase comparison means (336) coupled to said analog-to-digital converter for generating a digital signal that is proportional to the difference in phase between the signal generated by said digitizing means and a reference signal; and digital-to-analog converting means (340), responsive to the digital signals generated by said phase comparison means, for generating said analog control signal, said analog control signal conditioning the variable oscillator to change the frequency of said oscillatory signal in a sense tending to cause the signals provided by said phase comparison means to converge to a predetermined value.
Claim 3
Dependent Claim
71 words
A phase locked loop system as set forth in claim 1 wherein said digitizing means further includes a tracking filter (346) coupled to said analog-to-digital converter (344) and responsive to the signals provided thereby for developing a further digital signal representing said oscillatory signal and having a finer quantization resolution than the signal provided by said analog-to-digital converter, wherein said further digital signal is the output signal of said digitizing means.
Claim 4
Dependent Claim
167 words
A phase locked loop system as set forth in claim 2 wherein said tracking filter (346) includes a digital phase locked loop comprising: a digital oscillator (430) responsive to said clock signal (CK) and to a frequency control signal for developing a digital signal having substantially the same frequency as the signal provided by said analog-to-digital converter (344) and including M-bit digital samples, where M is an integer greater than N; phase comparison means (410) coupled to said digital oscillator (430) and to said analog-to-digital converter (344) for developing a signal proportional to the difference in phase between the respective signals provided thereby; and a low-pass filter (412) coupled to said phase comparison means for integrating the phase difference signal provided thereby to develop said frequency control signal for said digital oscillator; wherein said digital phase locked loop has a time constant sufficient to track any phase changes in the oscillatory signal provided by the digital oscillator that are related to frequency instabilities in the clock signal.
Claim 5
Dependent Claim
301 words
In a digital video signal processing system including a source (300) of clock signal (CK) which may exhibit frequency instabilities and a source (330) of digital chrominance signals (CB) including a color reference burst signal component, apparatus for demodulating said chrominance signals into first and second (I,Q) quadrature phase related color difference signals, characterized by the combination of; an analog variable oscillator (342) responsive to a control signal for developing a variable frequency oscillatory signal wherein the frequency of said oscillatory signal is substantially independent of said clock signal; digitizing means including an analog-to-digital converter (344) coupled to said analog oscillator for developing a first digital signal including plural-bit digital samples representing said oscillatory signal at instants in time determined by said clock signal; means (348) coupled to said digitizing means for developing a second digital signal having substantially the same frequency as, and being quadrature phase related to said first digital signal; first and second signal multiplying means (334, 332) coupled to receive said digital chrominance signals (CB) at respective first input ports and said first and second digital signals at respective second input ports for providing said first and second color difference signals (I,Q) at respective output ports; phase detecting means (336) coupled to said first and second signal multiplying means for developing a signal proportional to the difference between the phase of the vector sum of the components of said first and second color difference signals corresponding to said color reference burst signal and a reference phase value; and means coupled to said phase detecting means and including a digital-to-analog converter (340) responsive to said phase difference signal for developing said control signal for said analog variable oscillator to change the frequency of said oscillatory signal in a sense which reduces the amplitude of said phase difference signal.
Claim 6
Dependent Claim
301 words
In a digital video signal processing system including a source (300) of clock signal (CK) which may exhibit frequency instabilities and a source (330) of digital chrominance signals (CB) including a color reference burst signal component, apparatus for demodulating said chrominance signals into first and second (I,Q) quadrature phase related color difference signals, characterized by the combination of; an analog variable oscillator (342) responsive to a control signal for developing a variable frequency oscillatory signal wherein the frequency of said oscillatory signal is substantially independent of said clock signal; digitizing means including an analog-to-digital converter (344) coupled to said analog oscillator for developing a first digital signal including plural-bit digital samples representing said oscillatory signal at instants in time determined by said clock signal; means (348) coupled to said digitizing means for developing a second digital signal having substantially the same frequency as, and being quadrature phase related to said first digital signal; first and second signal multiplying means (334, 332) coupled to receive said digital chrominance signals (CB) at respective first input ports and said first and second digital signals at respective second input ports for providing said first and second color difference signals (I,Q) at respective output ports; phase detecting means (336) coupled to said first and second signal multiplying means for developing a signal proportional to the difference between the phase of the vector sum of the components of said first and second color difference signals corresponding to said color reference burst signal and a reference phase value; and means coupled to said phase detecting means and including a digital-to-analog converter (340) responsive to said phase difference signal for developing said control signal for said analog variable oscillator to change the frequency of said oscillatory signal in a sense which reduces the amplitude of said phase difference signal.
Claim 7
Dependent Claim
66 words
Apparatus as set forth in claim 4 wherein said digitizing means further includes a tracking filter (346) coupled to said analog-to-digital converter (344) and responsive to the signals provided thereby for developing said first digital signal representing said oscillatory signal, having a finer quantization resolution than the signal provided by said analog-to-digital converter, wherein said further digital signal is the output signal of said digitizing means.
Claim 8
Dependent Claim
157 words
Apparatus as set forth in claim 5 wherein said tracking filter (346) includes a digital phase locked loop comprising: a digital oscillator (430) responsive to said clock signal and to a frequency control signal for developing a digital signal having substantially the same frequency as, and a larger number of bits per sample than the signal provided by said analog-to-digital converter (344): phase comparison means (410) coupled to said digital oscillator and to said analog-to-digital converter for developing a signal proportional to the difference in phase between the respective signals provided thereby; and a low-pass filter (412) coupled to said phase comparison means for integrating the phase difference signal provided thereby to develop said frequency control signal for said digital oscillator (430); wherein said digital phase locked loop has a time constant sufficient to track any phase changes in the oscillatory signal provided by said digital oscillator that are related to frequency instabilities in the clock signal.
References Cited (Backward Citations)
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