HP 8112A Operating, Programming And Servicing Manual page 201

Servicing the Timing and
Slope Generators
Theory of Operation
Introduction
Trigger Input
The majority of the timing and slope generation circuit components
are on the main board A l . A small part of the associated circuitry,
concerned with burst control, is on the control board A2. Operation
of the timing and slope circuits is explained under the following
functions:
•
Trigger input
•
Address decoder
•
Control input
•
Timing IC (General)
•
Period, Width and Delay generation
•
Slope generation
•
Error feedback
The trigger input level circuit provides the required trigger-level to
the period generator without affecting the external trigger source.
When enabled by TON, the External Input signal from the front
panel is buffered by Op-amp Ul lOB and shifted to produce an input
in the range -4.3 V to +0.4 V for the TRIG IN input for the period
generator U200. The actual triggering level is controlled by the front
panel level control R119, via Op-amp U l lOA. When the external
trigger signal matches the selected level, Ul lOB applies an input
voltage of approximately - 1 .3 V to pin 7 of the period generator
U200.
Trigger mode
Trigger mode selection (positive, negative, gate etc.) is performed by
the timing IC U200, in conjunction with the mode decoder circuit
UlOl and U102 (see "Mode and Range Decoders" and Figure 10.3- 1)
to provide the type of trigger selected.
1 0 . 3
Servicing the Timing and 1 0.3-1
Slope Generators