Tektronix 184, Инструкция по эксплуатации

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Circuit Description-Type 1 84
10 MHz sine wave. This waveform is then differentiated by
the coupling networks and appears at the emitter of 0103
as a positive going .1
fLS
time marker.
.5
f.Ls
(-+-
5)
Countdown
Cou ntdown is ach ieved by the bucket and ladle action
of C105 and C1 07-C108. C105 dumps its charge each .1
fLS
through 01 14 into a pair of capacitors C107 and C108,
until enough charge has been built up so that the 5th
charge from C1 05 triggers the blocking oscil lator 0120.
This occurs each .5
fLS
and provides the .5
fLS
time markers.
The voltage step from the .1
fLS
shaper amplifier is also
applied through C105 to the emitter of 01 1 4. The posi­
tive 1
fLS
pulse turns 01 14 on and dumps a charge into
C107 and C1 08. The negative portion of the input signal
reverse biases the emitter-base junction. The junction then
acts in the manner of an approximate 6 V Zener diode to
clamp the negative portion of the input waveform.
These input charges on the ladle capacitor C1 05, build
a staircase ramp voltage across C1 07 and C1 08. The am­
pl itude of the ramp is governed by the base-to-emitter bias
of 0120 and the size of the bucket capacitors. At approxi­
mately 1 1 volts the emitter-base junction is forward biased
and transistor 01 20 turns on.
Feedback from transformer T1 1 5 drives the transistor to
saturation and generates a sharp positive-going pulse. Di­
ode D 115 prevents negative voltage excursions at the out­
put of the transformer. The positive output pu lse from
0120 is appl ied through Cl 1 6 to the base of emitter-fol­
lower 01 23. The resultant output markers from the emitter
of 0123 are delayed approximately 76 ns by delay line
1123A to al low stacking with other selected time markers.
1 f.Ls
(-+-
2) Countdown Circuit
0130, T130 and associated circuitry form a sing le-shot
blocking oscillator with an RC circuit determ ining the hold­
off time of the oscillator. This allows every other .5
fLS
time-marker input pulse to cycle the osci llator and produce
the 1
fLS
markers.
The first .5
fLS
marker pulse drives 0130 into conduction.
Feedback from the transformer T130 drives the transistor
to saturGltion. Capacitor C1 30 is charged to approximately
10 volts during this on time. When the transformer field
collapses and drives 01 30 to the off state, the decay­
ing charge on C130 will prevent the second .5
fLS
time mark
from' triggering 0130 on. When the third input .5
fLS
time
mark occurs, (C130 will have discharged sufficiently so that
01 30 is enabled) 0130 is driven into conduction and the
cycle repeats.
The negative pulse generated at the col lector of 0130
for every other input pu lse is amplified and inverted by
0134, then applied through emitter fol lower 0133, to the
MARKER SELECTOR switch, through an approximate 1 4 ns
delay line L123B. The 1
fLS
markers are also applied to the
TRIGGER SELECTOR switch through R1 36 as 1
fLS
trigger
signals. Multiple time-mark signals selected by the MARKER
SELECTOR switch are isolated from the Trigger Pickoff and
the next countdown stage by diode 01 37.
3-2
5 f.Ls
(+
5) Countdown
This circuit (01 45, 0155 and associated circuitry) is a
monostable mu ltivibrator that flips with an input trigger
pulse and remains in this state until the charge on the col­
lector-to-base coupling capacitor (C1 43) decreases to the
level that will permit the multi to return to its qu iescent state.
The 5th trigger then starts the cycle again.
In the quiescent state 01 55 is conducting, 0 1 45 is off.
An input positive signal to the base of 0145 turns 0145
on and 01 55 off. The resultant positive signal at the col­
lector of 01 55 is an approximate 1 2 volt square wave,
with a duration determined by the time constant of C143,
R1 45 and R146. This time constant· al lows the ...;- 5 count­
down from 1
fLS
to 5
fLS
markers. The output signal at the
col lector of 01 55 is differentiated by C152 and R1 54, with
the negative portion clamped to ground by diode D1 52.
The positive portion of the differentiated signal is applied
to both the emitter-follower 0153 and the next countdown
circuit. Diode D152 will also protect the base emitter junc­
tion of 01 53 from breakdown, due
.10
the back voltage
developed when C152 is discharged.
1 0 f.Ls to 1 0 ms Countdown Circuits
These circuits are identical to the above 5
fLS
countdown
circuit with the exception of the countdown time constant
that determines the holdoff time of each counter.
50 ms
to
5 s Countdown Circuits
These circuits are identical to the previous monostable
multivibrators; however, they are mounted on the second
board with the power supply circuits and high-ampl itude
marker amplifier. The 50 ms and .5 s countdown multivibra­
tors contain calibration adjustments to set the holdoff time of
the ...;- 5 multivibrators.
The series matching resistors in the time-marker Plath
to the MARKER SELECTOR switch provide current summing
in the base of the emitter followers for stacking time markers
at the output.
Marker Amplifier
The ampl ifier provides positive or negative time markers
of 25 volts minimum ampl itude (into 1 kO).
Marker intervals from 1
fLS
to 5 s selected by the push­
button MARKER SELECTOR switch are applied through the
first section of polarity switch SW450 to 0454. 0454 is
biased to remove the lower portion of the positive input
time-marker signal. This together with the speed-up ca­
pacitor C452 across limiting resistor R452, provides a narrow
time marker at the output.
Inverter amplifier (0464) emitter bias is such that only
the narrow portion of the input pulse turns the transistor on.
The positive output time marker from the inverter amplifier
or, (if the switch is in the (-) position), the output signal
from 0454, is applied to the base of the complimentary
emitter-follower stage, 0463 and 0473.
The complimentary emitter-follower stage provides ample
current for the added capacitance of most coaxial cables
®I