Chroma amplifier and color killer

In a color television receiver, a chroma amplifier and color killer, comprising:

• first and second emitter-coupled transistors receiving a source current which includes a D.C. operating current and an A.C. chroma signal current;
• means for coupling to the base of said first transistor an ACC voltage which is filtered to remove noise and high frequency components;
• means for coupling to the base of said second transisor a D.C. bias voltage which may include noise components;
• third and fourth emitter-coupled transistors receiving a source current which includes only a D.C. operating current of substantially the same amplitude as the D.C. operating current received by said first and second transistors;
• means for coupling said ACC voltage to the base of said fourth transistor;
• means for coupling said D.C. bias voltage to the base of said third transistor so that said fourth transistor develops a D.C. output signal which includes substantially no A.C. component and whose amplitude varies with variations in the ACC voltage;
• means for combining a collector output of said first transistor with a collector output of said third transistor so that an AC chroma output signal is developed whose amplitude is controlled by the ACC voltage, which includes substantially no ACC-induced D.C. variations, and in which amplified noise from the bias voltage appears in opposite, cancelling polarities;
• a D.C. actuated color killer adapted to normally supply operating current to a further chroma amplifier;
• and
• means for coupling said D.C. output signal to said color killer so that said color killer terminates the operating current supplied to the further chroma amplifier when said D.C. output signal reaches a predetermined level.

In a color television receiver having a color killer and a chroma amplifier, the latter comprising first and second emitter-coupled transistors and third and fourth emitter-coupled transistors interconnected and adapted to receive and amplify a chroma input signal, the improvement comprising:

• means for supplying a first current source to the emitters of the first and second transistors, said first current source including a D.C. operating current and an A.C. chroma current;
• means for applying a variable, filtered ACC voltage to the base of the first transistor;
• means for supplying a D.C. bias voltage which may include noise to the base of the second transistor;
• means for supplying a second current source to the emitters of the third and fourth transistors, said second current source including only a D.C. operating current substantially equal in magnitude to the D.C. operating current supplied to the first and second transitors;
• means coupling said D.C. bias voltage to the base of the third transistor;
• means coupling the ACC voltage to the base of said fourth transistor such that the fourth transistor develops a D.C. output signal for control of the color killer, which output signal includes substantially no A.C. component and whose amplitude varies with variations in the ACC voltage;
• and
• means coupling the collector of the first transistor to the collector of the third transistor to provide an ACC-controlled chroma output-signal having a substantially constant D.C. level and in which amplified noise from said bias voltage appears in opposite, cancelling polarities.