Method and apparatus for independently transmitting and recapturing clock recovery burst and DC restoration signals in a MAC system

• US 5,208,659 A
• Filed: 12/07/1989
• Issued: 05/04/1993
• Est. Priority Date: 06/03/1986
• Status: Expired due to Term

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Scientific-Atlanta Incorporated (Cisco Systems, Inc.)
• Inventors: Rhodes, Charles W.
• Primary Examiner(s): Shepperd, John W.
• Application Number:
  US07/445,101
• Time in Patent Office: 1,244 Days
• Field of Search: 358/14, 358/19, 358/20, 358/34, 358/12
• US Class Current: 348/479
• CPC Class Codes: H04N 7/083 with signal insertion during the vertical and the horizontal blanking interval , e.g. MAC data signals

Abstract

The present invention is directed to improving immunity to channel distortions of multiplexed analog component television signals by independently transmitting a clock recovery burst and a DC restoration reference level during the horizontal blanking interval of a video line. More particularly, the clock recovery burst and the DC restoration reference level are transmitted on independent lines. The integrity of the television receiver'"'"'s system is not compromised if the clock recovery burst is not transmitted on every line. Accordingly, the problems inherent in the prior art are avoided by independently transmitting the clock recovery burst and the DC restoration reference level on separate lines during a portion of the horizontal blanking interval of the respective lines. The clock recovery burst and the DC restoration reference level could be transmitted on alternate lines or the clock recovery burst could be sent every Nth line with the DC restoration reference level transmitted on lines therebetween.

Claims

1. In a frequency modulated time division multiplexed analog component video signal having a line which includes a luminance component, a chrominance component and a horizontal blanking interval which comprises either a clock recovery burst or a DC restoration level, but not both, the method of transmitting multiple lines of the video signal comprising the steps of:

transmitting a first line of the video signal wherein the horizontal blanking interval comprises the clock recovery burst; and

transmitting N subsequent lines of the same video signal wherein

a) N is an integer greater than 1 and less than the number of lines per field in the video system, and

b) the horizontal blanking interval comprises the DC restoration reference level.

2. The method of claim 1, wherein N=2.

3. The method of claim 1, wherein the DC restoration reference level is a signal corresponding to 50 IRE.

4. The method of claim 3 wherein N=2.

5. The method of claim 1, wherein the DC restoration reference level is a fixed level substantially above 100 IRE.

6. The method of claim 5, wherein N=2.

7. The method of claim 1, wherein the DC restoration reference level is a fixed level substantially below 0 IRE.

8. The method of claim 7, wherein N=2.

9. In a video signal receiver for receiving multiple lines of a frequency modulated time division multiplexed analog component video signal having either a clock recovery burst or a DC restoration reference level transmitted during a predetermined portion of each line'"'"'s horizontal blanking interval, a device for recapturing the clock recovery burst and the DC restoration reference level comprising:

first pulse generating means for generating a first enable pulse whose timing and duration correspond substantially to the predetermined portion of each line'"'"'s horizontal blanking interval;

second pulse generating means having first and second output ports for generating a second enable pulse having a duration corresponding to the transmitted line time and alternately outputting said second enabled pulse at said first and second output ports after every N line time durations;

first coincidence gate coupled to said first pulse generating means and the first output port of said second pulse generating means to output a first gating signal during the coincidence of said first enable signal and said second enable signal at the first output port;

first gating means coupled to said first coincidence gate for receiving the transmitted video lines and outputting a portion of the video line corresponding to said first gating signal;

second coincidence gate coupled to said first pulse generating means and the second output port of said second pulse generating means to output a second gating signal during the coincidence of said first enable signal and said second enable signal at the second output port; and

second gating means coupled to said second coincidence gate for outputting a reference level value signal corresponding to the duration of said second gating signal.

10. The device of claim 9, wherein N=1.

11. The device of claim 9, wherein N=2.

12. The device of claim 9, wherein the transmitted video lines are received at said second gating means.

13. The device of claim 9, wherein said portion of the video line corresponding to said first gating signal output from said first gating means is the clock recovery burst.

14. The device of claim 9, wherein said reference level value signal corresponding to the duration of said second gating signal output from said second gating means in the DC restoration reference level.

15. The device of claim 14, wherein said reference level value signal has a value of 50 IRE.

16. The device of claim 14, wherein said reference level value signal has a fixed value substantially above 100 IRE.

17. The device of claim 14, wherein said reference level value signal has a fixed value substantially below 0 IRE.