Overload Evaluation in Reverse Gain-Controlled Transistor Video If Amplifiers

It is generally recognized that if overload can be prevented, reverse-bias (gain decreases as emitter current decreases) in gain-controlled transistorized video IF amplifiers is preferred because of the superior bandpass stability throughout the AGC range and because of the uniformity in AGC tracking. Evaluation of overload distortion as a function of gain-control and source impedance indicates what signal levels can be tolerated at various operating conditions. Design based on overload evaluation has resulted in four-stage, 45 MHz amplifiers for color receivers having 70 db power gain, 60 db gain reduction capability, signal handling capability of 400 millivolts at the IF input of 50 ohms, and linear output capability of 3. 5 volts of video at 2900 ohms.