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ntroduction
This section contains the theory of operation of the various
circuits in the Type 114. The text is supplemented by two
block diagrams inserted in the text and by schematics in
ection 5. The reader should follow the circuits on the dia
grams as they are presented in the text.
CAUTION
There is no fixed chassis ground for the circuit
board used in the Type 114. A common negative
point is used instead.
This permits changing the
polarity of the output by grounding the appro
priate side of the power supply. For this reason,
always connect probe grounds to the main chassis
rather than to a point on the circuit board.
Period Generator
The Period Generator (see Fig. 3-1) supplies the trigger
pulse which activates the Width Generator. The trigger pulse
is generated internally, or is derived from an externally gen
erated triggering signal, depending upon the setting of the
PERIOD switch.
nternal Operation. When the Type 114 is operating in
the internally triggered modes, the operation of the Period
Generator is as follows:
Transistors Q 1 15 and Q125 in conjunction with the ap
propriate RC timing combination form a free running oscil
lator. At the start of a cycle of operation, Q 1 15 is biased off
and Q125 is biased slightly on. The charge on timing ca
pacitor C 1 15 has been removed by the preceding cycle and
now starts charging toward a common point voltage at an RC
rate. As the timing capacitor charges, the voltage across it
reaches a point where it turns on diode D 1 14 and transistor
Q 1 15. At this instant the circuit becomes regenerative with
Q 1 15 turning Q125 on hard, which in turn biases Q 1 15 into
heavy conduction. The heavy conduction of Q 1 15 removes
the charge accumulated on timing capacitor C 1 15 and ends
the cycle.
At the instant Q 1 25 is turned on hard by Q 1 15, the steep
wave-front is coupled through R131 and C 1 31 to the base of
Q 1 34, and thence to pulse transformer T131. The pulse out
put of T131 is in the order of 20 nanoseconds in width.
External Trigger Operation. When the Type 114 is op
erating in the externally triggered mode, the Pulse Generator
functions as a pulse shaper.
nects the base of Q 1 15 from the collector of Q 1 25 and re
connects it to the external trigger input circuit.
connects the base of Q 1 25 to +25 volts through R121 and
disconnects the timing capacitor from the circuit.
these conditions none of the transistors in the Period Gen
erator are conducting. A positive pulse of 2 to 20 volts in
amplitude and having a risetime of 1 microsecond or less
is required at the EXTERNAL TRIGGER — INPUT connector
SECTION 3
CIRCUIT DESCRI TION
Period switch
W120 discon
W120 also
Under
in order to make the transistors conduct and deliver the
proper pulse to the Width Generator.
When a pulse having the proper amplitude and risetime is
applied
to
the
EXTERNAL TRIGGER — INPUT connector,
Q 1 15 is biased into conduction and in turn biases Q 1 25
and Q134 into conduction. The resulting pulse at the pri
mary of T131 has a risetime of about 10 nanoseconds.
Width Generator
The Width Generator receives the trigger pulses from
T131 and generates pulses of the desired width. The out
put of the width generator is applied to the Trigger Out
Circuit and to the Output Amplifier.
ing
in
the
square wave
operates as a monostable multivibrator; in the square wave
mode the Width Generator functions as a bistable.
Normal
Operation.
In
Q205 and Q215 form a bistable network whose output
drives ramp transistor Q224, trigger output transistor Q234,
and the output amplifier. Q205 is the normally " on" tran
sistor.
The arrival of a negative trigger pulse from T131
cuts off Q205.
Q215 now conducts and cuts off Q224,
permitting the voltage at the collector of Q224 to start
charging ramp capacitor C 1 95.
capacitor reaches the desired voltage, D 1 93 is forward
biased and transistor Q 1 94 is biased into conduction. The
conduction of Q 1 94 increases the conduction of Q 1 84 and
thereby biases Q205 back into conduction. The conduction
of Q205 ends the output pulse.
off Q215 and turns on Q224. The conduction of Q224 dis
charges the ramp capacitor.
When the ramp capacitor is discharged down to about
0.3 volt, Q174 turns off and Q164 is turned on. Transistors
Q 1 64 and Q 1 74, diodes D 1 36 and D 16 1, and pulse trans
former T131 function as a pulse steering circuit. With Q 1 64
on, the pulse from the Period Generator via T131 triggers
the width monostable circuit on, generating an output pulse.
As soon as the ramp capacitor reaches approximately 0.3
volt, Q174 conducts and turns Q164 off. Turning off Q164
reverse biases D 1 61, while turning on Q 1 74 biases D 1 36
near zero. If the Period Generator produces a pulse while
these conditions exist, that is, whenever the ramp capacitor
has a charge above approximately 0.3 volt, the pulse is
steered to the WIDTH > PERIOD light circuit. This mono
stable circuit is actuated by the pulse from T131, turning
off Q145 and turning Q155 on, lighting the WIDTH >
PERIOD light. Turning on Q 1 55 causes C 1 55 to discharge
through T131 and R136. When C155 is discharged, D141
and Q 1 45 conduct and reset the circuit, making it ready
for another pulse.
Square Wave Mode.
When the Type 114 is operated
in the
quare Wave Mode (see Fig. 3-2), the Width Gen
erator operates as a bistable and requires two trigger pulses
from the Period Generator for each cycle of operation.
Consequently, the RC network in the Period Generator is
Except when operat
mode, the Width
Generator
normal
operation
transistors
When the selected ramp
Turning on Q205 turns
3-1
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