Deflection control circuit for image pick-up tube

Abstract

A circuit for controlling the deflection of an electron beam in an image pick-up tube of the electro-static deflection type including a target electrode, a cathode electrode for generating the electron beam, and deflection plates for causing the electron beam to scan the target electrode, the circuit including a current source transistor for generating a current, a first capacitor for storing a voltage corresponding to the generated current, a pair of switching transistors for generating a saw-tooth signal in accordance with the voltage stored by the capacitor and for supplying the saw-tooth signal to the deflection plates for causing the beam to scan an effective image area on the target electrode, a transistor for increasing the amount of current generated by the current source transistor when the effective image area is not being scanned, a circuit for discharging the capacitor during only a portion of the time period when the effective image area is not being scanned and for clamping the level of the saw-tooth signal to an over-scan start potential, and a circuit for clamping the level of the signal to an effective scan start potential when the electron beam begins scanning the effective image area, wherein the electron beam is caused to scan an over-scan area outside the effective image area at a rate faster than used to scan the effective image area so as to neutralize charges in the over-scan area which tend to distort the electron beam.