Apparatus for suppressing overshoots in kinescope beam current measurement pulses

Abstract

Display apparatus includes a kinescope cathode current sensor (,) coupled to a load (,) for developing a beam current measurement pulse during a beam current measurement interval. Overshoots in the pulses are suppressed by a pulse correction circuit (,) comprising a first capacitor (Ca) coupled from the load circuit (,) to a source of reference potential (Gr) via a switch (Q,); and a control circuit (Ca, Ra, Rb), responsive to the presence of the overshoot, for closing the switch for a predetermined length of time and for opening the switch otherwise. In an advantageous implementation of the pulse correction circuit the switch comprises a bipolar transistor (Q,) having an emitter (E) coupled to the source of reference potential (Gr) and having a collector (C) AC coupled to the load circuit (,) via the first capacitor (Ca); and the control circuit comprises a second capacitor (Cb) for AC coupling said load circuit to a base (B) of the bipolar transistor and a resistor (Ra) for DC coupling said base (B) to said source of reference potential (Gr). In an alternative irrplementation of the pulse correction circuit the switch comprises a field effect transistor (,A) provided with a gate (G) to drain (D) bypass diode (D,).