DC Coupled Video Amplifier
Original Publication Date: 1987-Sep-01
Included in the Prior Art Database: 2005-Feb-01
The video amplifier circuit disclosed reduces DC drift so that the known DC voltage at the input determines the DC operating point of the whole amplifier, so removing the need for DC restoration circuits, while retaining the required bandwidth and allowing voltage-operated gain control. The input stage is an asymmetric long-tailed pair with gain control which is independent of bias current. The output stage is an NPN-PNP cascode with complementary emitter followers at the output. Video amplifiers for modern color CRT displays require a gain of about 100 in each of the three color channels, combined with a pass band extending from DC to 30 MHz or more. Furthermore, an electrically controlled gain control is needed so that contrast can be adjusted simultaneously in all three channels by a remote contrast control.