Internal Trigger Amplifier

The Internal Trigger Amplifier converts the differential current input from the Trigger Pickoff circuit to a zero-referenced, single-ended output for use by the Trigger Level Comparator. Differential signals from the Pickoff Amplifier circuit are connected via R421 and R422 to common-base transistors U421E and U421D respectively. Transistor U421C and R428 constitute an inverting-feedback amplifier that converts U421D collector current to a voltage at the collector of U421C. This voltage is added in phase with the voltage drop across R427 produced by the signal current of U421E. The resulting sum is a single-ended voltage signal that is applied to the base of emitter-follower U421 A. The emitter-follower stage provides a low-output-impedance signal source that drives both the XY Amplifier (through R701) and emitter-follower U421B. The output signal from U421B is applied to the Trigger Source Switching Diode circuit at the cathode of CR440 where it is available for selection as the triggering signal.

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