Signal gain control with DC compensation

In a television receiver system for processing an image representative video signal having periodically recurring image intervals, and image blanking intervals between adjacent image intervals and comprising a black level reference interval, apparatus comprising:

• a source of video signals;
• video signal processing means responsive to said video signals and including:
• amplifier means with associated bias means for establishing the DC bias of said amplifier means;
• and
• gain control means with associated bias means for establishing the DC bias of said gain control means, said gain control means providing a gain control signal for controlling the gain of said amplifier means and also providing a DC compensation signal for said amplifier means such that the DC output level of said amplifier means is compensated to remain substantially constant as said amplifier means is gain controlled in response to said gain control signal;
• means, operative during said black level reference interval of said video signal, for comparing a voltage representative of said DC bias of said amplifier means with a voltage corresponding to a voltage representative of said DC bias of said gain control means, for providing an output control voltage representative of a deviation of said bias of said amplifier means and said bias of said gain control means from a prescribed mutual relationship;
• charge storage means coupled to the output of said comparing means for developing and storing a voltage corresponding to said control voltage representative of said deviation;
• and
• means for coupling said stored voltage to said video signal processing means with a sense for correcting said deviation.

In a television receiver system for processing an image representative video signal having periodically recurring image intervals, and blanking intervals containing a black level reference interval between adjacent image intervals, apparatus comprising:

• a source of video signals;
• charge storage AC signal coupling means having an input coupled to said source of video signals, and an output;
• video signal processing means responsive to AC coupled output signals from said AC coupling means and including:
• amplifier means with associated bias means for establishing the DC bias of said amplifier means;
• and
• gain control means with associated bias means for establishing the DC bias of said gain control means, said gain control means providing a gain control signal for controlling the gain of said amplifier means and also providing a DC compensation signal for said amplifier means such that the DC output level of said amplifier means is compensated to remain substantially constant as said amplifier means is gain controlled in response to said gain control signal;
• comparator means, operative during said black level reference interval of said video signal, for comparing a voltage representative of said DC bias of said amplifier means with a voltage corresponding to a voltage representative of said DC bias of said gain control means, for providing an output control voltage representative of a deviation of said bias of said amplifier means and said bias of said gain control means from a prescribed mutual relationship;
• and
• means of coupling said output control voltage to said AC coupling means for modifying the charge stored thereby with a sense for modifying said bias of said amplifier means in a direction for correcting said deviation.

Signal processing apparatus comprising:

• a source of input signals;
• signal processing means responsive to said input signals and including:
• first signal translating means with associated bias means for establishing the DC bias of said first translating means;
• and
• second signal translating means with associated bias means for establishing the DC bias of said second translating means;
• sensing means responsive to a voltage representative of said DC bias of said first translating means and to a voltage representative of said DC bias of said second translating means, for providing an output control voltage representative of a deviation of said bias of said first translating means and said bias of said second translating means from a prescribed mutual relationship;
• and;
• means for coupling said control voltage to said signal processing means for correcting said deviation.