Phase distortion detection circuitry for low cost automatic equalizer

• US 4,424,533 A
• Filed: 09/30/1981
• Issued: 01/03/1984
• Est. Priority Date: 07/10/1981
• Status: Expired due to Fees

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Rzeszewski, Theodore S.
• Primary Examiner(s): Murray, Richard
• Application Number:
  US06/306,967
• Time in Patent Office: 825 Days
• Field of Search: 358/35, 358/10, 358/139, 358/153, 358/160, 358/167, 358/187, 455/304, 455/305
• US Class Current: 348/614
• CPC Class Codes: H04N 5/14 Picture signal circuitry for video frequency region cameras or camera modules comprising electronic image sensors, or control thereof H04N23/00

Abstract

A system for detecting phase distortion in video signals due to multipath effects includes circuitry for extracting the high and low frequency content of a horizontal synchronization signal, and for comparing the phase of the high frequency content to the low frequency content to produce a signal indicative of phase distortion in the video signal. The phase distortion signal may be applied to distortion reduction circuitry, and specifically in a three tap delay line equalizer, to reduce phase distortion in the video signal.

Claims

1. A system for detecting and reducing phase distortion in video signals due to multipath effects, comprising means for providing a horizontal synchronization pulse portion of said video signal having a predetermined phase relationship between high and low frequencies contained in said horizontal synchronization pulse portion prior to transission thereof, means for measuring the phase of said high frequencies relative to said low frequencies to thereby provide a correction signal indicative of said phase distortion, and means coupled to receive said correction signal and said video signal for reducing said phase distortion in said video signal in accordance with the correction signal.

2. In a delay line equalizer having an N tap delay line for equalizing phase distortion in video signals due to multipath effects, a system for detecting said phase distortion comprising means for providing a selected portion of said video signal having a predetermined phase relationship between high and low frequencies contained in said selected portion prior to transmission thereof, and means for measuring the phase of said high frequencies relative to said low frequencies to thereby provide an indication of said phase distortion.

3. The equalizer of claim 2, wherein said delay line has no more than three taps.

18. The system of any one of claims 2, 3, 5 and 6, wherein said selected portion is a horizontal synchronization pulse portion of said video signal.

4. A system for detecting and reducing phase distortion in a video signal due to multipath effects, comprising:

means for providing a horizontal synchronization pulse portion of said video signal having a predetermined relationship between high and low frequencies contained in said horizontal synchronization portion prior to transmission thereof;

means for providing a signal related to the high frequency components of said horizontal synchronization pulse portion;

means for developing timing signals relative to said horizontal synchronization pulse portion;

output means responsive to said signal related to said high frequencies and under the control of said timing signals for providing a correction signal indicative of said phase distortion; and

means coupled to receive said correction signal and said video signals for reducing said phase distortion in said video signal in accordance with said correction signal.

7. The system of any one of claims 4, 5 or 6, wherein said output means comprises a gate receiving said signal related to the high frequency components and controlled by said timing signals for producing a gated output signal, and a filter for receiving said gated output signal.

8. The system of claim 7, wherein said means for providing a signal related to the high frequency components comprises means for adding said separated high frequencies to a delayed version thereof to produce said signal related to said separated high frequencies.

9. The system of claim 7, wherein said signal related to said separated high frequencies is identical to said separated high frequencies.

10. The system of any one of claim 4, 5 or 6, wherein said means for developing timing signals includes means for substantially differentiating signals related to said selected portion to provide a differentiated signal.

11. The system of claim 10, wherein said means for developing timing signals further includes timing circuitry for receiving said differentiated signal and for providing precise timing signals to said output means.

12. The system of claim 10, wherein said signal related to said selected portion is identical to said selected portion of said video signal.

13. The system of claim 10 further comprising a low pass filter receiving said selected portion for providing a filtered signal and wherein said signal related to said selected portion is said filtered signal.

14. The system of claim 10 further comprising a delay device receiving said selected portion and providing a delayed replica thereof, and said signal related to said selected portion is said delayed replica.

15. The system of any one of claims 4, 5 or 6, wherein said means for providing a signal related to said high frequency components comprises filter means for low pass filtering said selected portion for providing a filtered signal and subtraction means for subtracting said filtered signal from said selected portion.

16. The system of claim 15, wherein filter means comprises a Gaussian-like low pass filter.

17. The system of claim 16, wherein said selected portion is delayed in a delay device prior to being applied to said subtractor means to thereby compensate for a delay in said low pass filter.

19. The system of claim 7, wherein said selected portion is a horizontal synchronization pulse portion of said video signal.

20. The system of claim 10, wherein said selected portion is a horizontal synchronization pulse portion of said video signal.

21. The system of claim 15, wherein said selected portion is a horizontal synchronization pulse portion of said video signal.

5. In a delay line equalizer having an N tap delay line for equalizing phase distortion in video signals due to multipath effects, a system for detecting said phase distortion comprising:

means for providing a selected portion of said video signal having a predetermined phase relationship between high and low frequencies contained in said selected portion prior to transmission thereof;

means for providing a signal related to the high frequency components of said selected portion;

means for developing timing signals relative to said selected portion; and

output means responsive to said signal related to said high frequencies and under the control of said timing signals for providing a signal indicative of said phase distortion.

6. The equalizer of claim 5, wherein said delay line has no more than three taps.

22. A system for detecting phase distortion in video signals due to multipath effects, comprising:

means for providing a selected portion of said video signal having a predetermined phase relationship between high and low frequencies contained in said selected portion prior to transmission thereof;

first low pass filter means for filtering said selected portion to provide a filtered version of said selected portion;

delay means for delaying said selected portion an amount approximately equal to the delay in said first low pass filter means to provide a delayed version of said selected portion;

subtractor means for subtracting said filtered version of said selected portion from said delayed version of said selected portion to provide a difference signal;

means for developing timing signals relative to said selected portion;

second low pass filter means having a signal input and a signal output; and

gating means receiving said difference signal and said timing signals for delivering said difference signal to said signal input of said second low pass filter under the control of said timing signals, whereby said signal output of said second low pass filter is indicative of phase distortion in said video signal.

23. A system for detecting phase distortion in video signals due to multipath effects, comprising:

means for providing a selected portion of said video signal having a predetermined phase relationship between high and low frequencies contained in said selected portion prior to transmission thereof;

first low pass filter means for filtering said selected portion to provide a filtered version of said selected portion;

first delay means for delaying said selected portion an amount approximately equal to the delay in said first low pass filter means to provide a delayed version of said selected portion;

subtractor means for subtracting said filtered version of said selected portion from said delayed version of said selected portion to provide a difference signal;

second delay means for delaying said difference signal to provide a delayed version of said difference signal;

adder means for adding said difference signal and said delayed version of said difference signal to provide a summation signal;

means for developing timing signals relative to said selected portion;

second low pass filter means having a signal input and a signal output; and

gating means receiving said summation signal and said timing signals for delivering said summation signal to said signal input of said second low pass filter under the control of said timing signals, whereby said signal output of said second low pass filter is indicative of phase distortion in said video signal.