Video amplifier for combining luminance and chrominance signals

Abstract

A video amplifier circuit for combining chrominance and luminance signal components and for supplying resultant color representative signals to an image reproducing cathode ray tube comprises first, second and third transistors direct current coupled in series relation with a load circuit across an operating voltage (B+) supply. The first and second transistors are of one conductivity (NPN) while the third is of opposite conductivity (PNP). Luminance signals, which are direct current coupled to the third transistor (a voltage follower), are converted by means of a drive control resistor to provide luminance current drive to the other series connected transistors. Chrominance signals are direct current coupled to the control (base) electrode of the first transistor which operates in conjunction with the second transistor as a cascode voltage amplifier for chrominance signal components. Color signals are direct current coupled from the output of the upper (common base) transistor of the cascode amplifier to the cathode ray tube. The common base transistor is biased at a relatively low voltage to permit use of a relatively inexpensive wide bandwidth device for the lower transistor of the cascode arrangement.