Patent ID: 6151080
Filing Date: 2000-11-21
Classification: H04N

Abstract:
A demodulator for a chrominance signal, the demodulator comprising:a controlled frequency oscillator with a loop input, an adjustment input, and an output;a phase comparator with a first input connected to the oscillator output, a second input to receive a chrominance signal with a modulation frequency, and a current output operatively connected to the loop input of the oscillator;a fixed current source, also connected to the loop input of the oscillator, the fixed current source providing a fixed current;first and second output branches which comprise first and second calibration resistors respectively in series with a common resistor and a common current generator outputting a current equal to twice the fixed current; anda current mirror to copy a current equal to the sum of the fixed current and a current at the current output of the phase comparator, into the first and second output branches;a value of the first calibration resistor being such that a first output voltage measured across the first calibration resistor is equal to a first value determined when the modulation frequency of the signal applied to the second input of the phase comparator is equal to a central modulation frequency corresponding to a first color, and a value of the second calibration resistor being such that a second output voltage measured across the second calibration resistor is equal to a second value determined when the modulation frequency of the signal applied to the second input of the phase comparator is equal to a central modulation frequency corresponding to a second color.