Automatic frequency compensation of video signals transmitted across cables
View Patent ↗Systems and methods to provide automatic compensation for frequency attenuation of a video signal transmitted over a cable are provided. Frequency compensation is applied to a received video signal that was transmitted over the cable to thereby produce a compensated video signal. A shape of a horizontal sync portion of the compensated video signal is analyzed. The frequency compensation is automatically adjusted based on the shape of the horizontal sync portion of the compensated video signal. This abstract is not intended to be a complete description of the various embodiments of the present invention.
1. A method to provide automatic compensation for frequency attenuation of a video signal transmitted over a cable, comprising:
frequency compensating a received video signal that was transmitted over a cable to produce a compensated video signal;
producing a first voltage signal indicative of a level of a horizontal sync portion of the compensated video signal before it has settled;
producing a second voltage signal indicative of a level of the horizontal sync portion of the compensated video signal after it has generally settled, or indicative of an average level of the horizontal sync portion of the compensated video signal;
integrating a difference between the first and second voltage signals to produce a compensation control signal; and
automatically adjusting the frequency compensating based on the produced compensation control signal.
2. The method of claim 1 , wherein the automatically adjusting step causes a slope of a sync tip of the horizontal sync portion of the compensated video signal to be within a specified minimum acceptable slope.
3. The method of claim 1 , wherein the second voltage signal is indicative of the level of the horizontal sync portion of the compensated video signal after it has generally settled.
4. The method of claim 1 , wherein the second voltage signal is indicative of the average level of the horizontal sync portion of the compensated video signal.
5. A system to provide automatic compensation for frequency attenuation of a video signal transmitted over cable, comprising:
means for frequency compensating a received video signal that was transmitted over a cable to produce a compensated video signal;
means for producing a first voltage signal indicative of a level of a horizontal sync portion of the compensated video signal before it has settled;
means for producing a second voltage signal indicative of a level of the horizontal sync portion of the compensated video signal after it has generally settled, or indicative of an average level of the horizontal sync portion of the compensated video signal;
means for integrating a difference between the first and second voltage signals to produce a compensation control signal; and
means for automatically adjusting the frequency compensating based on the produced compensation control signal.
6. The system of claim 5 , wherein a the second voltage signal is indicative of the level of the horizontal sync portion of the compensated video signal after it has generally settled.
7. The system of claim 5 , wherein the second voltage signal is indicative of the average level of the horizontal sync portion of the compensated video signal.
8. The system of claim 5 , wherein the means for frequency compensating comprises an equalizer.
9. A system to provide automatic compensation for frequency attenuation of a video signal transmitted over cable, comprising:
an equalizer that frequency compensates a received video signal that was transmitted over a cable to produce a compensated video signal;
a compensation controller that
produces a first voltage signal indicative of a level of a horizontal sync portion of the compensated video signal before it has settled;
produces a second voltage signal indicative of a level of the horizontal sync portion of the compensated video signal after it has generally settled, or indicative of an average level of the horizontal sync portion of the compensated video signal; and
integrates a difference between the first and second voltage signals to produce a compensation control signal;
wherein the frequency compensation provided by the equalizer is automatically adjusted based on the compensation control signal produced by the compensation controller.
10. The system of claim 9 , wherein the compensation controller includes:
a sync separator that receives the compensated video signal and outputs a horizontal sync signal indicative of the presence of the horizontal sync portion of the compensated video signal;
a timing circuit that receives the horizontal sync signal and outputs a first trigger signal and a second trigger signal;
a first hold circuit that samples or tracks the compensated video signal in response to the first trigger signal and outputs the first voltage signal;
a second hold circuit that samples or tracks the compensated video signal in response to the second trigger signal and outputs the second voltage signal; and
a differential integrator that receives the first and second voltage signals and outputs the compensation control signal that adjusts the compensation provided by the equalizer.
11. The system of claim 10 , wherein:
the first trigger signal includes a first pulsed waveform that selectively closes a switch of the first hold circuit; and
the second trigger signal includes a second pulsed waveform that selectively closes a switch of the second hold circuit.
12. The system of claim 9 , wherein:
the second voltage signal is indicative of the level of the horizontal sync portion of the compensated video signal after it has generally settled.
13. The system of claim 9 , wherein:
the second voltage signal is indicative of the average level of the horizontal sync portion of the compensated video signal.
14. The system of claim 9 , wherein the equalizer provides optimal compensation when the compensation control signal output by the differential integrator reaches a steady state.