Method and apparatus for DC restoration using feedback
First Claim
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1. A feedback circuit for compensating for DC offset in an output signal comprising:
- a bi-level sync signal detection circuit configured to generate a bi-level sync signal detection pulse upon detection of a bi-level sync signal in said output signal;
a first delay circuit for delaying said bi-level sync signal detection pulse a first period of time;
a tri-level sync signal detection circuit configured to generate a tri-level sync signal detection pulse and disabling said bi-level sync signal detection pulse upon detecting a presence of a tri-level sync signal in said output signal during said first period of time;
a clamp pulse generation circuit for generating a clamp pulse upon receiving said bi-level sync detection pulse or said tri-level sync signal detection pulse;
a sampling circuit configured to sample said output signal during a time period of said clamp pulse to obtain a DC offset value;
a compensation circuit for applying an inverse of said DC offset value to said input signal.
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Abstract
A feedback circuit for restoration of DC in video signals is presented. A sample pulse representing the back porch of an incoming video signal is generated from the horizontal sync signal. The sample pulse triggers a sample and hold circuit to acquire the correct offset voltage in the output signal during this back porch period. The offset voltage feeds back through a summing node upstream of either the circuit causing the offset or an input amplifier thereby restoring the video signal to the desired DC voltage level with respect to ground.
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Citations
10 Claims
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1. A feedback circuit for compensating for DC offset in an output signal comprising:
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a bi-level sync signal detection circuit configured to generate a bi-level sync signal detection pulse upon detection of a bi-level sync signal in said output signal; a first delay circuit for delaying said bi-level sync signal detection pulse a first period of time; a tri-level sync signal detection circuit configured to generate a tri-level sync signal detection pulse and disabling said bi-level sync signal detection pulse upon detecting a presence of a tri-level sync signal in said output signal during said first period of time; a clamp pulse generation circuit for generating a clamp pulse upon receiving said bi-level sync detection pulse or said tri-level sync signal detection pulse; a sampling circuit configured to sample said output signal during a time period of said clamp pulse to obtain a DC offset value; a compensation circuit for applying an inverse of said DC offset value to said input signal. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A method for compensating for DC offset in an output signal comprising:
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generating a bi-level sync signal detection pulse upon detection of upon detection of a bi-level sync signal in said output signal; delaying said bi-level sync signal detection pulse a first period of time; generating a tri-level sync signal detection pulse disabling bi-level sync signal detection pulse upon detecting a presence of a tri-level sync signal in said output signal during said first period of time; generating a clamp pulse upon receiving said bi-level sync detection pulse or said tri-level sync signal detection pulse; sampling the output signal during a time period of said clamp pulse to obtain a DC offset value; subtracting said DC offset value from the input signal. - View Dependent Claims (9, 10)
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Specification