Bias control apparatus for a data slicer in an auxiliary video information decoder

• US 5,666,167 A
• Filed: 10/25/1996
• Issued: 09/09/1997
• Est. Priority Date: 09/15/1992
• Status: Expired due to Term

• Current Assignee: Thomson Consumer Electronics Incorporated (Vantiva SA)
• Original Assignee: Thomson Consumer Electronics Incorporated (Vantiva SA)
• Inventors: Tults, Juri
• Primary Examiner(s): Kostak, Victor R.
• Application Number:
  US08/738,118
• Time in Patent Office: 319 Days
• Field of Search: 348/465, 348/463, 348/468, 348/478, 348/473
• US Class Current: 348/465
• CPC Class Codes: H04N 5/18 by means of "clamp" circuit operated by switching circuit
• CPC Class Codes: H04N 7/0355 for discrimination of the binary level of the digital data, e.g. amplitude slicers

Abstract

An auxiliary video information decoder for extracting an auxiliary video information signal from a video signal includes a data slicer and apparatus for adjusting the slicing level of the data slicer. The slicing level is adjusted rapidly until a reference component of the auxiliary information signal is detected during a display interval of the video signal in which auxiliary video information is expected to occur. A count is incremented after display intervals in which the reference component is detected and is decremented after display intervals in which the reference component is not detected. Slicing level adjustment ceases while the count is at least a predetermined number. The apparatus rapidly adapts the slicing level to long-term video signal amplitude changes of significant magnitude (e.g. following a channel change) and maintains a constant slicing level when transient variations occur in the video signal amplitude.

Claims

1. Apparatus for processing a video signal having a reference signal component included in a plurality of horizontal display intervals of said video signal, said apparatus comprising:

means responsive to said video signal for producing an output signal having signal transitions corresponding to respective signal transitions of said reference signal component that cross a reference level;

means for modifying said reference level in response to a control signal;

a counter responsive to said output signal for producing a count representative of a number of said signal transitions of said output signal that occur during each interval included in said plurality of horizontal display intervals; and

control means for determining after each interval included in said plurality of horizontal display intervals whether said count equals a predetermined value, for determining after said plurality of horizontal display intervals a frequency of occurrence of said count being equal to said predetermined value, and for generating said control signal to modify said reference level after said plurality of horizontal display intervals in response to said frequency of occurrence being less than a predetermined frequency of occurrence.

2. The apparatus of claim 1 wherein

said control means produces a second count in response to said count produced by said counter;

said second count has a value corresponding to a value of said reference level;

said control means produces said control signal in response to said second count; and

said control means changes said second count in only one direction for increasing said reference level and for decreasing said reference level.

3. The apparatus of claim 1 wherein

said control means produces a second count in response to said count produced by said counter;

said control signal comprises a digital signal representative of said second count; and

said reference level modifying means comprises a digital-to-analog converter responsive to said digital signal for producing said reference level.

4. The apparatus of claim 1 wherein

said control means produces a second count;

said control means modifies said second count in a first direction when said count produced by said counter equals a first predetermined value;

said control means modifies said second count in a second direction opposite to said first direction when said count produced by said counter does not equal said first predetermined value; and

said control means generates said control signal to modify said reference level when said second count is a second predetermined value after said plurality of horizontal display intervals.

5. The apparatus of claim 4 wherein

said control signal represents a third count having a value corresponding to a value of said reference level;

and

said control means increases and decreases said reference level by changing said third count in only one direction.

6. The apparatus of claim 5 wherein

said reference signal component exhibits a plurality of periodic amplitude variations during each interval included in said plurality of horizontal display intervals;

and

said count representative of said number of said signal transitions represents a number of amplitude variations in said output signal corresponding to respective ones of said periodic amplitude variations in said reference signal component.

7. The apparatus of claim 6 further comprising a filter means in said video signal path for substantially preventing amplitude variations in said video signal other than said periodic amplitude variations of said reference signal component from affecting said count representative of said number of said signal transitions;

said filter means comprising a low pass filter coupling said video signal to an input of said output signal producing means, and a spike filter coupling said output signal to said counter.

8. Apparatus for processing a video signal having a reference signal component included in a reference signal interval during each of a plurality of horizontal display intervals of said video signal, said apparatus comprising:

means for determining a number of signal transitions of said reference signal component that cross a reference level during each of said reference signal intervals; and

means for modifying said reference level after said plurality of horizontal display intervals in response to said number being less than a predetermined number during more than one of said reference signal intervals.

9. Apparatus of claim 8 further comprising means for providing an output signal having signal transitions produced in response to respective signal transitions of said reference signal component that cross a reference level;

and wherein

said means for determining said number of signal transitions comprises a counter responsive to said output signal for producing during each of said reference signal intervals a count representative of said number of signal transitions; and

wherein

said means for modifying said reference level comprises means for evaluating said count after each of said reference signal intervals and for determining how frequently said count represents said predetermined number.

10. Apparatus of claim 9 wherein

said means for evaluating said count comprises a second counter for producing a second count;

said second count being incremented after each of said reference signal intervals that produces a value of said first count less than said predetermined number;

said second count being incremented after each of said reference signal intervals that produces a value of said first count equal to or greater than said predetermined number;

said means for modifying said reference level increases said reference level in response to said first count being a first value after said more than one of said reference signal intervals and said number of said signal transitions crossing said reference level being less than said predetermined number during each interval included in said more than one of said reference signal intervals; and

said means for modifying said reference level decreases said reference level in response to said first count being a second value after said more than one of said reference signal intervals and said number of said signal transitions crossing said reference level being less than said predetermined number during each interval included in said more than one of said reference signal intervals.

11. Apparatus of claim 9 wherein said means for modifying said reference level causes a modification of said reference level without determining whether said modification should be an increase of said reference level or a decrease of said reference level.

12. Apparatus of claim 11 further comprising means for establishing said reference level in response to a binary value;

and wherein said means for modifying said reference level modifies said binary value in only one direction for increasing said reference level and for decreasing said reference level.

13. Apparatus of claim 9 wherein each horizontal display interval included in said plurality of horizontal display intervals occurs during a respective one of a plurality of video frame intervals included in said video signal;

said plurality of video frame intervals occurring consecutively in said video signal.

14. Apparatus for processing a video signal having a reference signal component occurring during a reference signal interval included in each of a plurality of horizontal display intervals of said video system, said apparatus comprising:

means for determining during each of said reference signal intervals whether said reference signal component exhibits a predetermined relationship to a reference level; and

means for modifying said reference level after a delay including said plurality of horizontal display intervals;

said delay beginning in response to said reference signal component and said reference level exhibiting a relationship other than said predetermined relationship;

said reference signal component and said reference level exhibiting said relationship other than said predetermined relationship during more than one of said reference signal intervals included in said delay.

15. Apparatus of claim 14 wherein

said means for performing said comparison comprises means for producing an output signal having signal transitions produced in response to signal transitions of said reference signal component that cross a reference level during each of said reference signal intervals;

said means for modifying said reference level comprises means responsive to said output signal for determining a number of said signal transitions of said reference signal component that cross said reference level during each of said reference signal intervals;

said delay beginning in response to said number being less than a predetermined number;

said number being less than said predetermined number during more than one of said reference signal intervals included in said delay.

16. Apparatus of claim 15 wherein

said means for determining said number of said signal transitions comprises a counter responsive to said output signal for producing a first count representative of said number of said signal transitions;

said means for modifying said reference level comprises means for evaluating said first count after each reference signal interval included in said plurality of horizontal display intervals, and for producing a second count representing a number of said reference signal intervals during which said first count represents said predetermined number.

17. Apparatus of claim 16 wherein said delay ends in response to said second count representing a second predetermined number.

18. Apparatus of claim 17 wherein

said means for modifying said reference level increases said reference level in response to said second count being said second predetermined number and said first count being a third predetermined number;

and

said means for modifying said reference level decreases said reference level in response to said second count being said second predetermined number and said first count being a fourth predetermined number.

19. Apparatus of claim 17 wherein said means for modifying said reference level causes a modification of said reference level without determining whether said modification should be an increase of said reference level or a decrease of said reference level.

20. Apparatus of claim 19 further comprising

means responsive to a control signal for producing said reference level;

and wherein

said means for modifying said reference level includes means for producing a third count representing a value of said control signal, and for modifying said third count for modifying said reference level;

said third count being modified in only one direction for increasing said reference level and for decreasing said reference level.

21. Apparatus for decoding auxiliary information included in a video signal comprising:

means for producing a first count representative of a number of signal transitions of said video signal that cross a reference level during each interval included in a plurality of intervals;

means responsive to a binary value for providing said reference level; and

control means responsive to said first count for modifying said binary value in only one direction for changing said reference level such that said first count tends to become a predetermined count;

said reference level being increased and decreased in response to said binary value being modified in only said one direction.

22. Apparatus of claim 21 wherein

each interval included in said plurality of intervals includes a respective portion of a reference signal component of said video signal;

each of said respective portions of said reference signal component comprises a plurality of periodic amplitude variations;

said means for producing said first count comprises a data slicer for providing an output signal having signal transitions produced in response to respective signal transitions of said video signal that cross said reference level; and

a counter responsive to said output signal for producing said first count;

said control means comprises means for evaluating said first count after each interval included in said plurality of intervals, and for producing a second count representing a number of said intervals during which said first count represents a predetermined number.

23. Apparatus of claim 22 wherein said control means modifies said binary value in response to said second count representing a second predetermined number.