US 3,961,361 A · Gain control arrangement useful in a television signal processing system

Abstract

In a color television receiver, first and second amplifiers are respectively included in the luminance and chrominance channels to permit control of contrast and saturation. The amplifiers have gain versus control voltage characteristics including linear portions extrapolated to cut off at predetermined voltages which may or may not be the same. A first potentiometer is coupled between a source of fixed voltage equal to the extrapolated cut off voltage of the first amplifier and a gain controlling voltage source. The gain controlling voltage may be produced by a circuit including an element responsive to ambient light. The wiper of the first potentiometer is coupled to the first amplifier to couple a voltage developed at a predetermined point of the first potentiometer to the first amplifier to control its gain. A second potentiometer is coupled between a source of voltage equal to the extrapolated cut off voltage of the second amplifier and the gain controlling voltage source to receive a portion of the gain controlling voltage in accordance with the ratio of the extrapolated cut off voltages of the first and second amplifiers. The wiper of the second potentiometer is coupled to the second amplifier to couple a voltage developed at a predetermined point of the second potentiometer to the second amplifier to control its gain. In this manner, the contrast of the receiver may be varied over a relatively wide range while saturation is maintained substantially constant.

Claims11

Dependent claims

In a color television signal processing system of the type including luminance and chrominance signal processing channels, apparatus comprising:

first and second amplifiers respectively included in said luminance and chrominance channels, said amplifiers having gain versus control voltage characteristics including linear portions extrapolated to cut-off at predetermined voltages which may or may not be the same voltage;
a gain controlling voltage source;
means for coupling said gain controlling voltage to said first amplifier to control its gain;
potentiometer means coupled between a fixed voltage substantially equal to the extrapolated cut-off voltage of said second amplifier and to said gain controlling voltage source to recieve a portion of said gain controlling voltage in accordance with the ratio of the extrapolated cut-off voltages of said first and second amplifiers;
and
means for coupling a voltage developed at a predetermined point on said potentiometer means to said second amplifier to control its gain.

3 more elements

Apparatus comprising:

first variable gain amplifying means for amplifying a first signal in response to a first DC control signal, said first amplifying means having a first gain versus DC control voltage characteristic including a linear region, said linear region having a gain substantially equal to 0 at a DC control voltage equal to V.sub.O ;
second variable gain amplifying means for amplifying a second signal in response to a second DC control signal, said second amplifying means having a second gain versus DC control voltage characteristic including a linear region, said linear region having a gain substantially equal to 0 at a DC control voltage equal to AV.sub.O, where A is a number greater than 0;
a first source of fixed voltage substantially equal to V.sub.O ;
a second source of fixed voltage substantially equal to AV.sub.O ;
means for developing a third DC control voltage v;
means for developing a portion Av of said third control voltage v;
first means for deriving said first control voltage including means for providing the difference between said third control voltage v and said fixed voltage V.sub.O and means for adding a predetermined portion of the difference between said third control voltage v and said fixed voltage V.sub.O to said DC control voltage v;
and
second means for deriving said second control voltage including means for providing the difference between a portion Av of said third control voltage v and said fixed voltage AV.sub.O and means for adding a predetermined portion of the difference between said portion Av and said fixed voltage AV.sub.O to said DC control voltage v.

6 more elements

Dependencies are inferred from the claim text.

Gain control arrangement useful in a television signal processing system

Life of this patent

Gain control arrangement useful in a television signal processing system

Life of this patent

Abstract

Claims11