Time base correction of television signals

Claim 2

A television signal processing system wherein a color video signal includes subcarrier frequency, sync and color burst components, characterised by means (14) for digitizing said sync and color burst signal components in accordance with a sampling clock, means (32) for measuring the difference between the phase of the color burst component and the phase o the sampling clock; and means (22-26) responsive to the phase difference to remove, in closed loop, phase errors from said digitized signal.

Claim 3

A television signal processing system as in claim 1, wherein said means (14) for digitizing said sync and color burst signals is an analog-to-digital converter.

Claim 4

A television signal processing system as in claim 1, including a high speed digital signal processor (20) for generating a frequency control word which is the resultant of the difference in phase between the color burst signal component and the sampling clock; and a frequency synthesizer (22) coupled to said processor for generating a sampling clock which has been phase corrected in response to said frequency control word.

Claim 5

A television signal processing system according to claim 3, wherein said high speed digital signal processor comprises a frequency accumulator (40,42) for generating said frequency control word, which is corrected on a line-by-line basis for application to said frequency synthesizer.

Claim 6

A television recording and playback system wherein input signals are processed, said signals including a nominal subcarrier frequency signal and color burst and horizontal sync components, the system including a time base correction circuit chracterized by: means (10) for delaying said input video signals to provide a delayed late video signal and an undelayed early video signal; a converter (14) for sampling said video signals in accordance with a sampling clock at a multiple frequency of said subcarrier and for converting said delayed and undelayed analog video signals to digital signals; a high speed digital signal processor (20) coupled to said converter for correcting the phase of the sampling clock and for providing a frequency control word; a frequency synthesizer (22) coupled to said processor for correcting the frequency of said sampling clock in response to said frequency control word; and means (26) operating at a multiple of the subcarrier frequency for locking the sampling clock to the video signal with correct phase and frequency on a line-by-line basis.

Claim 7

A television recording and playback system wherein input signals are processed, said signals including a nominal subcarrier frequency signal and color burst and horizontal sync components, the system including a time base correction circuit chracterized by: means (10) for delaying said input video signals to provide a delayed late video signal and an undelayed early video signal; a converter (14) for sampling said video signals in accordance with a sampling clock at a multiple frequency of said subcarrier and for converting said delayed and undelayed analog video signals to digital signals; a high speed digital signal processor (20) coupled to said converter for correcting the phase of the sampling clock and for providing a frequency control word; a frequency synthesizer (22) coupled to said processor for correcting the frequency of said sampling clock in response to said frequency control word; and means (26) operating at a multiple of the subcarrier frequency for locking the sampling clock to the video signal with correct phase and frequency on a line-by-line basis.

Claim 8

A system according to claim 5, including a video switch (12) coupled between said delaying means and said converter for switching between said delayed and undelayed signals at predetermined times.

Claim 9

A system according to claim 5, including a bandpass filter (18) coupled in a first channel to said converter for filtering noise from said color burst component and for producing two filtered video samples that are 90° apart.

Claim 10

A system according to claim 7, wherein said digital signal processor comprises a burst phase subtractor (36) coupled to said bandpass filter and a frequency accumulator (40,42) for correcting the sampling phase of said digitized burst signal.

Claim 11

A system according to claim 8, wherein said frequency accumulator (40,42) generates a frequency control word that is corrected on a line-by-line basis for application to said frequency synthesizer.

Claim 12

A system according to claim 8 or claim 9, including a clock-to-burst phase calculator (32) for processing filtered burst samples to develop an error signal representing phase error between the sampling clock and zero crossings of said burst signal components.

Claim 17

A system according to claim 14, wherein said frequency synthesizer includes a memory (48) for generating a sine waveform substantially without harmonics and having a phase representing the phase of said phase accumulator.

Claim 18

A system according to claim 15, including a digital-to-analog converter (50) coupled to said memory (48), and a low pass filter (52) coupled to said digital-to-analog converter and having a cutoff frequency so that a pure fundamental sine wave is produced.

Claim 20

A system according to claim 16, including means (62) for selecting burst zero crossings that are coincident with the horizontal sync pulses for generating a horizontal write pulse whereby phase adjustment may be achieved for the horizontal picture position.

Claim 23

A method according to claim 19, wherein the sampling clock operates at a frequency that is a multiple of said subcarrier frequency.