Tektronix 453 User Manual

I •NTENSITY I
Vertical Chopped
Blanking Signal
from Vertical Switching
Circuit
External Blanking
from Z
AXIS INPUT
Connector
A
and B
unblanking
gate from
Sweep
Generator
circuits
R1005
R1004
R1011
R1012
C1036
Circuit Description-Type 453/R453
+ 90 V to
r------"~ Geometry
Adjustment
Unblanking
gate to CRT
circuit
Fig.
3-15. Z Axis Amplifier detailed block diagram.
decreases the current through Ql 014 during the trace switch-
ing time to blank the
CRT display. The external blanking
input allows an external signal connected to the Z
AXIS
INPUT connector to change the trace intensity. A positive-
going signal connected to the Z
AXIS INPUT connector
decreases trace intensity and a negative-going signal
in-
creases trace intensity. The A and B unblanking gate signals
from the A and B Sweep Generator circuits blank the CRT
during sweep retrace and recovery time so there is no dis-
play on the screen. When the Sweep Generator circuits are
reset and recovered, (see A and B Sweep Generator dis-
cussion for more information) the next trigger initiates the
sweep and an unblanking gate signal
is generated in the
A or B Sweep Generator circuit that goes negative to allow
the emitter current to reach the
level established by the
INTENSITY control and the other blanking inputs.
Output Amplifier
The resultant signal produced from the various inputs by
the Input Amplifier stage
is connected to the base of Ql 024
through
Cl 029 and to the base of Ql 034 through Rl 024.
These transistors are connected as a collector-coupled com-
plementary amplifier. This configuration provides a linear,
fast output signal
with minimum quiescent power.
The Z Axis Amplifier circuit is a shunt-feedback operational
amplifier
with feedback from the Output Amplifier stage to
the Input Amplifier stage through
Cl 036-Cl 037-Rl 036. The
output voltage is determined by the input current times the
feedback resistor and
is shown by the fomula· E t - i· X
Rtb where Rtb is Rl 036. The unblanking input ~ur~uen~h~nge
is approximately two milliamperes. Therefore, the output
voltage change
is about 60 volts (2 mA X 30. l kn). Cl 036
®
adjusts the feedback circuit for optimum high-frequency re-
sponse.
Zener diode Dl 043 conneded between +75 volts and
+
150 volts through Dl 044, Rl 044 and Rl 043 produces a
+90-volt
level at the cathode of Dl 043. This voltage estab-
lishes the correct operating level for the Geometry adjust-
ment
in the CRT Circuit and establishes the correct collector
level for Ql 043. Dl 045 connected from base to emitter of
<?1043 improves the response of Ql043 to negative-going
signals. When the base of
Ql 043 is driven negative to cutoff,
Dl 045 is forward biased and conducts the negative-going
portion of the unblanking signal.
This provides a fast fall-
ing edge on the unblanking gate to quickly turn the display
off. The output unblanking gate at the emitter of Ql 043
is connected to the CRT circuit through Rl 046.
CRT CIRCUIT
General
The CRT Circuit provides the high voltage and control
circuits necessary for operation of the cathode-ray tube
(CRT). Fig. 3-16 shows a detailed block diagram of the CRT
Circuit. A schematic of this circuit is shown on diagram 16
at the rear of this manual.
High-Voltage Oscillator
0930 and associated circuitry comprise a class C oscilla-
tor10 to produce the drive for the high-voltage transformer,
T930. When the instrument is turned on, the current through
R925 charges C913 positive and Q930 is forward biased.
10
Lloyd P. Hunter, pp. 14-19-14-21.
3-23

Tektronix 453 Specifications

General

Brand	Tektronix
Model	453
Category	Test Equipment
Language	English