Device for correcting the color of a television signal according to NTSC standard
AssigneeSGS-Thomson Microelectronics S.A.
InventorYann Desprez-le Goarant
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Abstract
A device corrects the chrominance parameters transmitted by a chrominance subcarrier of a television signal, by shifting the phase of two demodulation signals an angle, which depends upon the phase of the chrominance subcarrier. The demodulation signals are obtained from a phase-locked loop including a resistive and capacitive network having two outputs that differ by 90° with respect to each other. The device may include circuitry for individually shifting the phase of each signal provided by the RC network by adding to each signal a fraction of the other signal provided by the RC network. The fractional coefficients may be opposite to each other and depend upon the phase of the chrominance subcarrier.
Claims56
A device for correcting an R-Y chrominance parameter and a B-Y chrominance parameter transmitted by a chrominance subcarrier of a television signal by producing a B demodulation signal and an R demodulation signal produced by shifting an S0 signal and an S90 signal, respectively, a phase shift amount which depends on the phase of the chrominance subcarrier, the S0 signal and the S90 signal being obtained from a phase locked loop including an RC network, the S0 signal and the S90 signal differing in phase by about ninety degrees, the device comprising:
- a first multiplying unit, having an output, to multiply the S90 signal by a first fraction;
- a first adder having a first input to receive the S0 signal, a second input coupled to the first multiplying unit output and an output to provide the B demodulation signal;
- a second multiplying unit, having an output, to multiply the S0 signal by a second fraction, the second fraction being equal in magnitude and opposite in sign to the first fraction;
- a second adder having a first input to receive the S90 signal, a second input coupled to the second multiplying unit output and an output to provide the R demodulation signal;
- and
- a control unit, coupled to the first multiplying unit and the second multiplying unit, to provide at least one reference value corresponding to the value of the first fraction and the second fraction.
A circuit to restore an R chrominance parameter and a B chrominance parameter from a television signal, comprising:
- a first node to receive an R reference signal;
- a second node to receive a B reference signal;
- a phase shift circuit, coupled to the first node and the second node and responsive to the phase of the television signal, to add a fraction of the B reference signal to the R reference signal to shift the phase of the R reference signal a phase shift amount to produce an adjusted R reference signal, and to add a fraction of the R reference signal to the B reference signal to produce an adjusted B reference signal;
- and
- a demodulator, having a first input to receive the television signal, a second input to receive the adjusted R reference signal and a third input to receive the adjusted B reference signal, to decode the television signal into the R chrominance parameter and the B chrominance parameter.
A circuit for correcting and decoding an input signal having a first parameter encoded with respect to a first reference phase and a second parameter encoded with respect to a second reference phase, comprising:
- a generation circuit to generate a first reference signal and a second reference signal;
- a phase shift circuit, coupled to the first reference signal and the second reference signal, and responsive to the phase of the input signal, to add a first fraction of the second reference signal to the first reference signal to shift the phase of the first reference signal a phase shift amount dependent on the phase of the input signal to produce a first adjusted reference signal, and to add a second fraction of the first reference signal to the second reference signal to produce a second adjusted reference signal;
- and
- a demodulator, having a first input to receive the input signal, a second input to receive the first adjusted reference signal and a third input to receive the second adjusted reference signal, to decode the input signal into the first parameter and the second parameter.
A method for restoring an R chrominance parameter and a B chrominance parameter from a television signal, comprising the steps of:
- providing an R reference signal;
- providing a B reference signal;
- after the step of providing an R reference signal, shifting the phase of the R reference signal an amount responsive to variations in the phase of the television signal to produce an adjusted R reference signal;
- after the step of providing a B reference signal, shifting the phase of the B reference signal approximately the amount to produce an adjusted B reference signal;
- and
- demodulating the television signal using the adjusted R reference signal and the adjusted B reference signal.
A method for adjusting the phase of a first signal, comprising the steps of:
- providing a second signal and an input signal;
- and
- adding a fraction of the second signal to the first signal, the magnitude of the fraction varying in response to variations in the phase of the input signal;
- wherein the adding a fraction step comprises the steps of:
- determining a first coefficient;
- multiplying the second signal by the first coefficient to produce a fractional signal;
- adding the fractional signal to the first signal;
- wherein the step of determining comprises the steps of:
- providing a first reference signal and a second reference signal;
- multiplying the first reference signal by the input signal to produce the first coefficient;
- multiplying the second reference signal by the input signal to produce a second coefficient;
- and
- wherein the multiplying the second signal step comprises the steps of:
- multiplying the first coefficient and the second coefficient to produce a combined coefficient;
- and
- multiplying the second signal by the combined coefficient.
A circuit for restoring an R chrominance parameter and a B chrominance parameter from a television signal comprising:
- means for shifting the phase of an R reference signal an amount in response to variations in the phase of the television signal to produce an adjusted R reference signal;
- means for separately shifting the phase of a B reference signal to produce an adjusted B reference signal;
- means for demodulating the television signal using the adjusted R reference signal and the adjusted B reference signal;
- wherein:
- the means for shifting the R reference signal comprises means for adding a first fraction of the B reference signal to the R reference signal, the magnitude of the fraction varying in response to variations in the phase of the input signal;
- and
- the means for shifting the B reference signal comprises means for adding a second fraction of the R reference signal to the B reference signal.
A circuit for restoring an R chrominance parameter and a B chrominance parameter from a television signal comprising:
- means for shifting the phase of an R reference signal an amount in response to variations in the phase of the television signal to produce an adjusted R reference signal;
- means for separately shifting the phase of a B reference signal to produce an adjusted B reference signal;
- means for demodulating the television signal using the adjusted R reference signal and the adjusted B reference signal;
- wherein the means for shifting the B reference signal comprises means for adding the second fraction of the R reference signal to the B reference signal, the second fraction being equal in magnitude to the first fraction.
A circuit for adjusting the phase of a first signal, comprising:
- means for receiving a second signal and an input signal;
- and
- means for adding a fraction of the second signal to the first signal, the magnitude of the fraction varying in response to variations in the phase of the input signal;
- wherein the means for adding comprises:
- means for determining a first coefficient;
- means for multiplying the second signal by the first coefficient to produce a fractional signal;
- means for adding the fractional signal to the first signal;
- wherein the means for determining comprises:
- means for receiving a first reference signal and a second reference signal, means for multiplying the first reference signal by the input signal to produce the first coefficient;
- further comprising:
- means for converting the first signal and the second signal into the first reference signal.
Dependencies are inferred from the claim text.