Back-porch clamp
AssigneeThomson Licensing
InventorRonald Thomas Keen
Life of this patent
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Abstract
The invention teaches a method, means and apparatus for clamping a back porch interval of a video signal including clamping a sync-tip level of said video signal to a variable reference voltage, comparing a back-porch voltage level of the sync-tip clamped video signal to a predetermined reference voltage, generating an error signal representative of the difference between the back-porch voltage level and the predetermined reference voltage, and adjusting the variable reference voltage in response to the error signal such that the error signal is minimized.
Claims15
Method of clamping a back porch interval of a video signal comprising:
- clamping a sync-tip level of said video signal to a variable reference voltage;
- comparing a back-porch voltage level of said sync-tip clamped video signal to a reference voltage;
- generating an error signal representative of the difference between said back-porch voltage level and said reference voltage;
- adjusting said variable reference voltage in response to said error signal for minimizing said error signal;
- and
- temporarily disabling said adjusting of said variable reference after initial application of said video signal.
Apparatus for adjusting a level of a video signal during a back-porch interval of a video signal comprising:
- means for adjusting a sync-tip level of said video signal in response to a variable reference voltage;
- means for comparing said back-porch level of said sync-tip level adjusted video signal during said sync-tip level adjusted video signal's back-porch interval to a reference voltage;
- means for determining a difference signal between said sync-tip level adjusted video signal during said sync-tip level adjusted video signal's back-porch interval to a reference voltage;
- means for determining a difference signal between said sync-tip level adjusted video signal's back-porch interval level and said reference voltage;
- means for controlling said variable reference voltage in response to said difference signal in such a way as to reduce said difference signal toward zero;
- and
- means for temporarily disabling said means for adjusting said sync-tip level of said video signal in response to said variable reference voltage after initial application of said sync-tip level adjusted video signal.
Apparatus for clamping a back-porch interval of a video signal comprising:
- a terminal for receiving said video signal;
- a keyed comparator for determining the difference between a level of said back-porch interval and a reference voltage, said keyed comparator having an output for providing a variable reference voltage;
- a sync-tip clamp, being configured to adjust the DC bias applied to said input video signal in an amount and of a polarity such as to cause said back-porch level to essentially equal said reference voltage in response to said keyed comparator output and a controller to temporarily disable said variable reference voltage after initial application of said video signal.
Dependencies are inferred from the claim text.