Jitter cancellation technique for video clock recovery circuitry

An apparatus for correcting time base errors in an audio-visual signal, the apparatus comprising:

• a. a ring oscillator having a plurality of taps wherein each tap provides a periodic clock signal having a same frequency and a relative phase;
• b. a multiplexor having a plurality of data inputs, an address input and an output wherein each tap of the ring oscillator is coupled to one of the plurality of data inputs of the multiplexor;
• c. a circuit for providing an address to the address input of the multiplexor based upon a time base error corresponding to a portion of an audio-visual signal wherein the circuit for providing an address comprises:
• i. a circuit for forming a first digital value representative of a time difference between an expected occurrence of a sync pulse corresponding to the portion of the audio-visual signal and an actual occurrence of the sync pulse;
• and
• ii. a circuit for adding the first digital value to a sum of previous digital values for forming the address, the circuit for adding coupled to the circuit for forming;
• and
• d. a circuit for forming a second digital value representative of an amplitude of a periodic waveform sampled according to a clock signal appearing at the output of the multiplexor, wherein the circuit for forming the second digital value is coupled to receive the first digital value.

A method of correcting time base errors in an audio-visual signal comprising steps of:

• a. forming a plurality of periodic clock signals, each having a same frequency and a relative phase;
• b. providing the plurality of clock signals to a corresponding plurality of data inputs of a multiplexor;
• c. providing an address to an address input of the multiplexor based upon a time base error corresponding to a portion of a first audio-visual signal wherein the step of providing an address comprises steps of:
• i. forming a first digital value representative of a time difference between an expected occurrence of a sync pulse corresponding to the portion of the first audio-visual signal and an actual occurrence of the sync pulse;
• and
• ii. adding the first digital value to a sum of previous digital values for forming the address;
• and
• d. forming a second digital value representative of an amplitude of a periodic waveform sampled according to a clock signal appearing at an output of the multiplexor, wherein the circuit for forming the second digital value is coupled to receive the first digital value.

An apparatus for correcting time base errors in an audio-visual signal, the apparatus comprising:

• a. a ring oscillator having a plurality of taps wherein each tap provides a periodic clock signal having a same frequency and a relative phase;
• b. a multiplexor having a plurality of data inputs, an address input and an output wherein each tap of the ring oscillator is coupled to one of the plurality of data inputs of the multiplexor;
• c. a circuit for providing a series of addresses to the address input of the multiplexor based upon a clock phase desired to appear at the output of the multiplexor;
• d. a circuit for providing a first series of digital values to the circuit for providing the series of addresses wherein each value in the first series is representative of a time base error corresponding to a portion of the audio-visual signal;
• and
• e. a circuit for providing a second series of digital values representative of a periodic waveform sampled according to the clock phase appearing at the output of the multiplexor wherein the circuit for providing the second series of digital values is coupled to receive the first series of digital values.

A method of correcting time base errors in an audio-visual signal comprising steps of:

• a. forming a clock signal wherein a phase of the clock signal is controlled according to a phase of a audio-visual signal having a varying time base;
• b. forming a first series of digital values, each of which represents a time base or phase error associated with a portion of the audio-visual signal;
• c. cumulating the first series of digital values for forming a first series of cumulated values wherein each of first series of cumulated values is representative of a phase change between successive cycles of the clock signal;
• d. cumulating the first series of cumulated values for forming a second series of cumulated values wherein each of the second series of cumulated values is representative of an accumulated phase of the clock signal;
• e. cumulating a fixed value thereby forming a series of values representative of a sawtooth waveform clocked according to the clock signal;
• and
• f. subtracting the each of the second series of cumulated values from each of the series of values representative of a sawtooth waveform thereby forming a series of difference values.