Voltage Gain; Output; Trigger Output Amplifier; Level Check Circuit - HP 8112A Operating, Programming And Servicing Manual

Trigger Output Amplifier

Level Check Circuit

10.4-6 Servicing the Shaper and Output Amplifier

Voltage gain

The signals from the input stage, generated across R524 and R527,
are applied to the bases of Q503 and Q504. These transistors operate
as emitter followers for Q505 and Q506 which provide the actual
voltage gain.

output

The output stage consists of the emitter-follower pairs Q510, Q512
and Q511, Q513. These decouple the voltage gain stage from the low
output-impedance.
The input to the trigger amplifier, derived from the period generator
is assed via a Schmidt trigger input Q280 and
(See Chapter 10.3), p
switched on and in turn switches Q283 off, to produce a low (0 V)
output.
When the circuit input goes low, Q282 is switched off allowing Q283.
to switch on and provide an output voltage of 2.4 V into 50 IR or
4.8 V into a high impedance.
Due to the inverting action of the trigger amplifier, the inverted
trigger input pulse is output as a positive going pulse, synchronized
to the output of the period generator. In normal mode the TRIG
OUT signal is a 50% duty cycle square wave at the same frequency
as the main HP 8112A output. In TRIG and GATE modes, the
TRIG OUT signal is a pulse-shaped equivalent of the trigger input.
The rising and falling edges correspond to the trigger level voltage
passing through the threshold level set by the TRIG LEVEL control.
This circuit is used during instrument self-test which is performed
at switch on, to verify the operation of the output amplifier and
pre-attenuator. For more details see the self-test routine described in
chapter 10.1.