Tektronix PG 508, Инструкция по эксплуатации

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TM 11-6625-2980-14
12 goes high during the pulse duration time and if pin 13
is low, pin 15 goes high and pin 14 low. Pin 13 controls
U400C in the square wave and external duration modes.
Duration and Delay Control Error Light Circuitry
This circuitry illuminates the CONTROL ERROR light
when the duration or delay times are greater than the
periods of their respective triggers. The positive pulse
from the duration generator is fed into the D input, pin
10, of U480A. The clock enable line is low. If the
duration time is set so that a trigger pulse (connected to
the clock in) for the next duration pulse occurs before
the output of the duration generator goes low, the high
on the D input, pin 10 of U480A, is transferred to the
output, pin 1. This high is connected to the set input, pin
5, of U480B which causes the output, pin 2, of U480B to
go high illuminating the error light. When the output, pin
2, of U480B goes high, the inputs to U480A and B are
disabled through the clock enable line preventing further
trigger inputs until both flip flops are reset. When the
output, pin 2, of U480B goes and stays high, C487 starts
to charge to the voltage on pin 2, through R490. This
takes approximately 100 ms. When the reset inputs to
U480A and B, pins 13 and 4, reach the high level (about
4.0 V) U480A and B are reset and C487 discharges
through R490. When these reset inputs return to the low
level both flip flops are ready to accept triggers and the
error cycle is ready to repeat. If the delay time is set for
a time greater than the period of the delay triggers, the
high on pin 7 of U480B transfers to pin 2 directly, and
the light is illuminated Reset takes place in the same
manner as described above. Also connected to this
circuitry is a line from the transition time board which
also lights the CONTROL ERROR light.
The CONTROL ERROR light is also illuminated for
certain improper control settings. Fig. 2-1 shows a
simplified schematic for the CONTROL ERROR
indicator logic and control settings causing illumination.
Variable Transition Time Circuitry
This circuitry controls the output transition times.
Resistors R534 and R536 provide equivalent 50 n
termination impedance for the normal (positive-going)
input from the duration generator. Also, R520 and R522
provide an identical termination impedance for the
complement input (negative-going) from the duration
generator. These inputs drive the bases of 0525 and
0530. When the input from the duration generator is
high and the complement is low, the collector of 0530
drops from ground to about -1/2 V. This turns Q565 on
and Q560 off. The adjustable constant current through
0545, to +15 V, is now passed through R578, from the -
15 V supply. Transistor Q560 is turned off as its base is
connected to ground Zener diodes VR620 and VR630
0635 and then through 0630to charge the particular
capacitor determined by the transition time selected. As
the capacitor charges through a constant current source,
the junction of CR584 and CR600 goes negative at a
linear rate until the diode CR600 turns on. This diode
serves as the negative clamp. The voltage at the anode
of CR600 is set by R615 through Q608 and 0600 The
voltage at the junction of CR584 and CR600 remains
low for the pulse duration.
lower the voltage from the bases of 0565 and Q560 to
the bases of 0625 and Q630 by about 7.5 V. Transistor
Q625 is therefore off and Q630 is conducting. Current
flows from -15 V through an adjustable current source
At the end of the pulse duration time, the collector of
0530 goes positive. This action turns 0565 off and Q560
on. Current from the +15 V supply flows through
constant current source 0545, then through 0560 raising
the1 junction of CR584 and CR600 at a linear rate
determined by the capacitor value and the current
available. The junction of CR584 and CR600 goes
positive until CR584 turns on. The voltage at the
cathode of CR584 is set by R570 through Q575 and
0580. Transistor 0625 is turned on, and Q630 off,
passing current from constant current source 0635
through 0625, CR604, and R604 to ground. The leading
and trailing transition times are varied independently by
varying the amount of current passing through constant
current source transistors 0635 and 0545.
The output waveform at the junction of CR584 and
CR600 passes to the gate of fet 0680. This fet serves as
a source follower for driving 0685 and Q690. These
transistors compose a linear differential amplifier. The
clamp levels for diodes CR584 and CR600 are set so
that Q685 and 0690 are slightly overdriven. This serves
to remove any ringing or other signal irregularities at the
top and bottom of the waveform. Operational amplifier
U665 provides, along with 0660, constant current for
0685 and Q690.
Transition Time Control Error Light Circuitry
This circuitry illuminates the control error light when
the leading transition time is greater than the pulse1
duration time, or when the trailing transition time is
greater than the pulse off time. The inverted signal from
the leading and trailing generator appears at the base of
0704 through fet follower 0700. A differential amplifier is
formed by 0704 and 0706. The output is taken from the
collector of Q706. Transistors 0704 and 0706 are over-
driven to reduce the window of comparison. During the
pulse on time, the base of 0704 is negative with respect
to ground. This action causes the collector of 0706 to
also go negative, driving the base of Q715, an emitter
follower negative. The emitter of Q715 is connected to
pins 7 and 10, the D input of flip flops U720A and B.
The waveforms driving the transition time circuitry are
also applied to gates U740A and B. Pin 6 of U740B is
high during pulse time while pin 4 of U740A is low. The
purpose of the four gates in U740 is to delay the signal
ap-
2-3