HP 8082A Operating And Service Manual page 26

4 - 1 0
External Input Amplifier
4-11
output of the rate generator is controlled, either gated or
triggered, by the external input amplifier. The amplitude
of the external input signal is limited by a bridge circuit
to approximately 2 2V. The signal then enters one side of
a differential amplifier, the reference voltage on the other
side of which is determined by the setting of the EXT.
TRIG LEVEL control. Thus the threshold level of the in-
put signal, i.e. the voltage level at which gating or trig-
gering occurs, can be varied. The SLOPE/POLARITY
switch determines whether a rising
RATE
- - L-
b
input signal will cause triggering or gating. If set to MAN,
the switch disables the external input signal and enables
the MANUAL button so that pressing the button simula-
tes one pulse from the external input.
4 - 1 2 Rate Generator
4 - 1 3 In the NORMAL mode, the output of the
pulse generator is derived from the rate generator. The
rate generator consists of a ramp generator which feeds
a Schmitt trigger to produce a 50% duty cycle square
wave output. A simplified diagram of the circuit is shown
in Figure 4-3.
ENABLE I DISABLE
FROM
MODE SWiTCH