Video imaging apparatus for distortion correction in cathode-ray tubes, use a semiconductor switch to disable the dynamic focus voltage during kine bias measurement

摘要

The video imaging apparatus consists of cathode-ray tube with a focus electrode, a focus voltage correction signal source, and an amplifier (97) responsive to the correction signal. A switch (Q13) is coupled to the path of the correction signal, is used to disable the focus voltage component during a kine bias measurement interval. A signal source is used to indicate the end time of a vertical blanking interval. A time-shifter, responsive to a clock signal, and the signal source to coupled to the switch to control when the dynamic focus voltage is enabled.