Tektronix 7613 User Manual

Circuit Description —7613/R7613 Service
Oscillator
Output Amplifier
Q1061, Q1066
Q1070, 01072
Output
Voltage
Divider
TU
ARE
Fig, 3-20. Calibrator detailed block diagram.
CALIBRATOR AND FRONT PANEL
SWITCHING
The Calibrator and Front Panel Switching circuit pro-
vides output voltage to the front-panel Calibrator pin-jacks
and includes the front-panel switches and controls. Fig. 3-20
shows a detailed block diagram of the Calibrator portion of
this circuit. A schematic of this circuit is shown on
diagram 7 at the rear of this manual.
Mode Switch Logic
The VERT MODE switch determines the operating
mode of the Vertical Interface circuit. The levels
established by this switch are also used in various other
circuits throughout this instrument. This switch is designed
so it is self-cancelling (i.e., only one button can be pressed
at a time). Specific operation of this switch is described in
connection with the circuits that it controls.
The TRIG SOURCE switch controls the operation of the
Trigger Selector circuit. This switch is also self-cancelling so
only one of the buttons can be pressed at a time. Operation
of this switch is discussed in connection with the Trigger
Selector circuit.
Calibrator
General. The Calibrator circuit provides accurate voltage
output at the front-panel Calibrator pin-jacks. Repetition
rate of the output signal is about one kilohertz.
Oscillator. 01061 and Q1066 are connected as a square-
wave oscillator to determine the repetition rate of the
Calibrator circuit. Oscillation occurs as follows: Assume
. that Q1061 is conducting and Q1066 is off. The collector
current of 01061 through R1061 produces a voltage level
which holds the base of Q1066 low. This keeps Q1066
turned off, and since there is no current through it, its
collector goes positive to produce the positive portion of
the square wave. At the same time, C1064 begins to charge
toward —15 volts through R1069. The emitter of Q1066
goes negative also as C1064 charges, until it reaches a level
about 0.6 volt more negative than the level at its base.
Then, Q1066 is forward biased and its emitter rapidly rises
positive. Since C1064 cannot change its charge instan-
taneously, the sudden change in voltage at the emitter of
Q1066 pulls the emitter of Q1061 positive aiso, to reverse
bias it. The current through Q1066 produces a voltage drop
at its collector to produce the negative portion of the
square wave.
Now, conditions are reversed. Since Q1061 is reverse
biased, there is no current through it. Therefore, C1064 can
begin to discharge through R1063. The emitter level of
Q1061 follows the discharge of C1064 until it reaches
about —0.6 volt. Then, 01061 is forward biased and its
collector drops negative to reverse bias Q1066. This
interrupts the current through Q1066, and its collector goes
positive again to complete the square wave. Once again,
C1064 begins to charge through R1069 to start the second
cycle. The signal produced at the collector of Q1066 has a
repetition rate of about one kilohertz.
The Oscillator stage can be changed by jumper P1066.
When this jumper is installed in the DC position, the
Oscillator is disabled and the collector of Q1066 rises posi-
tive. This produces a positive DC voltage output to the
front-panel Calibrator pin-jacks.
Output Amplifier. Transistors Q1070 and 01072 are
connected as a comparator with the reference level at the
base of Q1072 determined by the network R1073-R1074-
R1076-R1077. The 4 Volts adjustment R1077, is set to
provide accurate output voltage at the 4V Calibrator
pin-jack.
3-23
7613

Tektronix 7613 Specifications

General

Brand	Tektronix
Model	7613
Category	Test Equipment
Language	English