Phase modulation demodulator apparatus and method

The method of generating a decoding reference signal phase locked to a carrier reference signal, including the steps of;

• sampling the carrier reference signal to produce a set of samples,
• finding a phase increment value representative of the change of phase of said carrier reference signal from one sample to the next,
• setting said decoding reference signal to a known phase value,
• incrementing said known phase value of said decoding reference by the amount of said phase increment value.

The method of determining the sample to sample change of the phase of a sampled carrier reference including the steps of;

• sampling said carrier reference to produce said samples, determining the phase value of a first known sample from a known slope half cycle of said carrier reference,
• determining the phase value of a second known sample from a known slope half cycle of said carrier reference,
• determining the phase change of the carrier occurring from said first known sample and said second known sample,
• dividing said phase change by one more than the number of samples which occurred between said first known sample and said second known sample, said result being said sample to sample phase change.

The method of determining the sample to sample change of the phase of a sampled carrier reference including the steps of;

• sampling said carrier reference to produce said samples, determining the phase value of a first known sample from a known slope half cycle of said carrier reference,
• determining the phase value of a second known sample from a known slope half cycle of said carrier reference,
• determining the phase change of the carrier occurring from said first known sample and said second known sample,
• dividing said phase change by one more than the number of samples which occurred between said first known sample and said second known sample,
• obtaining said result number of times providing a set of results,
• determining a statistically representative value for said set, said statistically representative value being said sample to sample phase change.

The method of decoding a color video signal to recover the color difference signals modulated on a color subcarrier therein, including the steps of;

• generating a sampling clock phase locked to horizontal sync pulses of said color video signal,
• sampling said color video signal with an analog to digital convertor thereby producing digital samples thereof,
• filtering the color subcarrier out of the said digital samples thereby producing color samples,
• producing a burst flag in response to said horizontal sync pulses,
• computing a statistical representative value of the change of phase of the color burst from sample to sample in response to said color samples and said burst flag,
• generating a reference phase signal from a phase accumulator,
• incrementing the phase of said reference phase signal by the amount of said statistical representative value of the change of phase for each clock of said sampling clock,
• offsetting the value of said reference phase by a known amount,
• generating the sine and cosine values corresponding to the value of said reference phase at each new value thereof,
• multiplying each of said chroma samples by said sine value and by said cosine value thereby producing unfiltered color difference signals, and
• filtering said unfiltered color difference signals to produce said color difference signals.

The method of generating a reference subcarrier signal in response to a color video signal, including the steps of:

• generating a sampling clock and in response thereto sampling said color video signal and with an analog to digital convertor thereby producing digital samples thereof;
• providing color burst samples from said digital samples in response to the color subcarrier burst;
• generating a burst flag in response to predetermined synchronizing pulses of said color video signal;
• in response to said color burst samples and said burst flag, generating a sample phase value which is statistically representative of the change of phase of the color subcarrier burst from sample to sample;
• in response to said sample phase value, generating a reference phase signal in a reference generator, for at least some of said sampling clock, said reference generator operative to increment the phase of said reference phase signal by an amount which is directly responsive to said sample phase value thus producing a data stream of reference phase signal values;
• generating at least one corresponding sine value data stream in response to said reference phase signal value data stream, said data stream of said sine values representing said reference subcarrier signal.