Video signal converting device

Abstract

A video signal converting device is capable of converting an analog composite signal into a proper digital signal with a small delay even if the analog composite signal contains much jitter. The video signal converting device has a sampling clock output unit for outputting a sampling clock signal having a frequency which is 4n times the frequency of a burst signal contained in the analog composite signal (n represents a positive integer of 2 or greater), and an analog-to-digital converting unit for converting the analog composite signal into a digital signal based on the sampling clock signal output from the sampling clock output unit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a general arrangement of a video signal converting device according to the present invention.

FIG. 2 is a diagram illustrating a horizontal line and sample numbers of an NTSC signal.

FIG. 3 is a diagram illustrating details of a digital blanking period.

FIG. 4 is a diagram showing the positions and values of 10-bit samples in the digital blanking period.

FIG. 5 is a detailed block diagram of the video signal converting device.

FIGS. 6A and 6B are diagrams showing sampling timings of an NTSC signal.

FIGS. 7A and 7B are diagrams illustrating how to determine a sampling phase.

FIG. 8 is a diagram showing how a data interpolator/omitter operates when the number of samples in a one-line period is 910.

FIG. 9 is a diagram showing how the data interpolator/omitter operates when the number of samples in a one-line period is smaller than 910.

FIG. 10 is a diagram showing how the data interpolator/omitter operates when the number of samples in a one-line period is greater than 910.

FIG. 11 is a flowchart of an operation sequence for determining a sampling phase.

FIG. 12 is a flowchart of an operation sequence for correcting the number of samples.

Claims

1. A video signal converting device for converting an analog composite signal into a digital signal, comprising: sampling clock output means for outputting a sampling clock signal having a frequency which is 4n times the frequency of a burst signal contained in said analog composite signal (n represents a positive integer of 2 or greater); andanalog-to-digital converting means for converting said analog composite signal into a digital signal based on said sampling clock signal.

2. The video signal converting device according to claim 1, further comprising: digital signal extracting means for extracting every n digital values from a predetermined sampling phase of digital values output from said analog-to-digital converting means, and outputting the extracted digital values.

3. The video signal converting device according to claim 2, wherein said digital signal extracting means comprises: negative-going-edge detecting means for detecting a negative-going edge of a horizontal synchronizing signal of said analog composite signal;comparing means for comparing the digital values on the negative-going edge of the horizontal synchronizing signal with a sampling phase determining value; andsampling phase determining means for determining said sampling phase based on the result of the comparison from said comparing means.

4. The video signal converting device according to claim 2, further comprising: sample number correcting means for correcting the number of samples as the digital values output from said digital signal extracting means so as to be equal to a predetermined number in a one-line period of said analog composite signal.

5. The video signal converting device according to claim 4, wherein said sample number correcting means holds and outputs previously sampled digital values if the number of samples is smaller than said predetermined number, and deletes digital values if the number of samples is greater than said predetermined number.