Color demodulation for digital television
First Claim
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1. A digital sampling and color separation unit for a receiver of a composite video signal having a quadrature-modulated color subcarrier signal, comprising:
- an analog-to-digital converter that samples said video signal at a sampling frequency such that an integer number of samples are acquired in a time equal to an integer number, plus or minus 0.25, times the period of said subcarrier signal, thereby providing sampled video data;
a digital luminance-chrominance separator that receives said sampled video data and separates said sampled video data into luminance data and chrominance data;
a digital oscillator for providing phase reference values at said sampling frequency, each phase reference value representing a phase relationship between a sample of said chrominance data and said subcarrier signal, such that each chrominance sample has an associated phase reference value;
a memory, driven by said digital oscillator, that stores sin and cosine values and that matches said phase reference values to said sin and cosine values; and
a demodulator that receives said sin and cosine values and said chrominance data, multiplies each chrominance sample by a sin or a cosine value matched to the phase reference value associated with that sample, and low pass filters the product, thereby providing color difference data.
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Abstract
A digital sampling and separation unit (12) for a television receiver (10) of a composite video signal, such as an NTSC signal, which has a color subcarrier. The video signal is sampled at a frequency selected in accordance with the invention. This frequency provides samples having a definite and repeating phase relationship with the subcarrier signal. (FIG. 4). As a result, phase reference values can be used to convert the samples into correct color difference values.
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Citations
20 Claims
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1. A digital sampling and color separation unit for a receiver of a composite video signal having a quadrature-modulated color subcarrier signal, comprising:
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an analog-to-digital converter that samples said video signal at a sampling frequency such that an integer number of samples are acquired in a time equal to an integer number, plus or minus 0.25, times the period of said subcarrier signal, thereby providing sampled video data; a digital luminance-chrominance separator that receives said sampled video data and separates said sampled video data into luminance data and chrominance data; a digital oscillator for providing phase reference values at said sampling frequency, each phase reference value representing a phase relationship between a sample of said chrominance data and said subcarrier signal, such that each chrominance sample has an associated phase reference value; a memory, driven by said digital oscillator, that stores sin and cosine values and that matches said phase reference values to said sin and cosine values; and a demodulator that receives said sin and cosine values and said chrominance data, multiplies each chrominance sample by a sin or a cosine value matched to the phase reference value associated with that sample, and low pass filters the product, thereby providing color difference data. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A chrominance sampling and demodulation unit for a receiver of a composite video signal having a quadrature-modulated color subcarrier signal, comprising:
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an analog-to-digital converter that samples said subcarrier signal at a sampling frequency such that an integer number of samples are acquired in a time equal to an integer number, plus or minus 0.25, times the period of said subcarrier signal, thereby providing chrominance data; a digital oscillator that provides phase reference values at said sampling frequency, said phase reference values each representing a phase relationship between a sample of said chrominance data and said subcarrier signal, such that each chrominance sample has an associated phase reference value; a memory that stores sin and cosine values and matches said phase reference values to said sin and cosine values; a demodulator that receives said sin and cosine values and said chrominance data, multiplies each chrominance sample by a sin or a cosine value matched to the phase reference value associated with that sample, and low pass filters the product, thereby providing said color difference data. - View Dependent Claims (8, 9, 10, 11, 12)
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13. A method of providing color difference data in a receiver of a video signal having a quadrature-modulated color subcarrier signal, comprising the steps of:
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sampling said subcarrier signal, at a sampling frequency such that an integer number of samples are acquired in a time equal to an integer number, plus or minus 0.25, times the period of said subcarrier signal, thereby providing chrominance data; providing phase reference values at said sampling frequency, said phase reference values each representing a phase relationship between a sample of said chrominance data and said subcarrier signal, such that each chrominance sample has an associated phase reference value; matching said phase reference values to sin and cosine values; and multiplying each chrominance sample by a sin or a cosine value matched to the phase reference value associated with that sample; and low pass filtering the results of said multiplying step, thereby providing said color difference data. - View Dependent Claims (14, 15, 16)
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17. A digital television receiver of a video signal having a quadrature-modulated subcarrier signal for color difference information, comprising:
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a signal interface that receives and tunes said video signal; a sampling and color separation unit having; an analog-to-digital converter that samples said video signal at a sampling frequency such that an integer number of samples are acquired in a time equal to an integer number, plus or minus 0.25, times the period of said subcarrier signal, thereby providing sampled video data; a digital luminance-chrominance separator receives said sampled video data and separates said sampled video data into luminance data and chrominance data; a digital oscillator that provides phase reference values at said sampling frequency, said phase reference values each representing a phase relationship between a chrominance sample and said subcarrier signal, such that each sample of said chrominance data has an associated phase reference value; a memory that stores sin and cosine values and matches said phase reference values to said sin and cosine values; and a demodulator that receives said sin and cosine values and said chrominance data, multiplies each chrominance sample by a sin or a cosine value, and low pass filters the product, thereby providing color difference data; a pixel processor that receives said luminance data and said chrominance data and performs pixel processing tasks on said data; and a frame memory that provides said data to a display. - View Dependent Claims (18, 19, 20)
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Specification