Tektronix 114 User Manual

Circuit Description — Type 114
Fig. 3-1. Type 114 block configuration for pulse output.
reduced to half its normal value so that the Period Gen 
erator can deliver twice the usual number of output pulses.
This procedure ensures that the period indicated by the
PERIOD switch remains valid for square-wave operation.
(When external triggering is used, the period of the square
wave is twice that of the triggering signal, since the Width
Generator is functioning as a bistable and requires two
pulses for each cycle of operation.)
In the Width Generator, the ramp circuit is disabled by
D 1 96, which means that the comparator consisting of D 1 93,
Q 1 94, and Q 1 84 is not used. Resetting of the width bistable
is accomplished by applying the output of WIDTH > PERI 
OD light driver transistor Q155 to the base of Q125.
At the instant of turn on when operating in the square 
wave mode, D 1 77 reverse biases and Q 1 74 is biased on.
Q 1 74 turns off Q 1 64 and zero biases steering diode D 1 36.
Under these conditions, the first pulse from the Period Gen 
erator forward biases D 1 36 and turns off Q 1 45. Turning off
Q 1 45 turns on Q 1 55, which in turn cuts off Q215 and makes
Q205 the conducting transistor in the bistable. Turning
off Q215 also biases Q224 into conduction which switches
the steering circuit so that D 1 61 becomes zero biased. The
second pulse from the Period Generator is steered to Q205,
switching the bistable and the steering circuit. Thus the
output of the bistable is a symmetrical square wave.
Trigger Output Circuit
Trigger output transistor Q234 normally operates in satura 
tion due to the current through R232. Whenever the sig 
nal selected by the TRIGGER switch goes negative, the volt 
age change is coupled through C231 to the base of Q234
and momentarily takes it out of saturation. When this hap 
pens, the collector voltage of Q234 rises sharply until it
reaches ≈ 3 ½ volts and forward biases catcher diode
D236. The resulting trigger output through C236 is about
80 nanoseconds wide and is limited to ≈ +3 volts into
an open circuit, or to 10 ma into a short circuit.
The TRIGGER switch permits selecting the edge of the
output waveform at which the trigger occurs. By setting
the switch to TRAILING EDGE, the Type 114 may be used
as a delay generator with the WIDTH controls setting the
amount of delay.
Output Amplifier
The two-stage output amplifier consists of driver transistor
Q244 and the parallel-connected output transistors Q254
and Q264. When negative output pulses are desired, the
output transistors are connected common emitter and the
+25-volt supply is connected to chassis ground displacing
the circuit board common ground 25 volts negative. When
positive output pulses are desired, the output transistors are
connected as an emitter follower and the common point is
connected to chassis ground. Polarity switching of the out 
put is accomplished by the AMPLITUDE switch.
3-2

Tektronix 114 Specifications

General

Brand	Tektronix
Model	114
Category	Pulse Generator
Language	English