HP 3312A - Page 19

Model 3312A
determine the voltage at the base of U403(e) and in turn at
the base of U403(c). When the voltage from the main
generator (via the BUFFER AMPLIFIER) appearing at the
base of U403(b) equals that at the base of U403(c), both
U403(a) and (b) turn on and U403(c) turns off. CR408
forward biases and clamps the integrator output to the
voltage at the base of U403(c) (which was originally
determined by TRIGGER PHASE POT, RI16). With the
integrator output held at that level the comparator does not
switch the current sources resulting in a de level at the
square wave output. When the burst control goes low again
the voltage on the integrating capacitor will determine the
phase at which the burst restarts. Thus, R615 controls the
start/stop phase.
" 443. Multiple Cycle Burst Mode (Figure 7-3). The main
generator is gated off when the burst logic sees a positive
square wave transition after the burst input to U402 pin 2
goes high. If the main square wave is already high, the main
generator will not be gated off until the main square wave
first goes low then returns high. The waveforms in Figure
4-9 should serve to clarify the operation of the burst logic.
4-44. Single Cycle Burst Mode. In single cycle operation
(Figure 7-3), U402A pin 2 is driven from U401, a
monostable one-shot multivibrator. After being inverted the
output of U402 is normally high. Triggering of U401 causes
U402A pin 2 to go low for 40 nanoseconds, after which it
returns to its quiescent high state. This 40 nanosecond low
pulse is sufficient to start the main generator. Since pin 2
MAIN SQUARE
TP4
main ZN
TPS
BURST CONTROL
U40212)
INVERTED ONE ~
SHOT OUTPUT
U402(2)
SINGLE CYCLE
TRIGGER MODE
Section [V
FROM BURST CONTROL
OFREE RUN
TRIGGER PHASE &
mi7 V
FROM
BUFFER
AMP
FN
3312 —B - 4038 PHASE POT
Figure 4-8. U403 Burst Amplifier Array,
almost immediately returns to a high state, the main
generator runs until the triangle returns to its start/stop
phase position, at which time the generator stops, comple-
ting one cycle of operation.
S3124-B-4305
Figure 4-9. Burst Time Relation Waveforms.