TM 11-6625-2735-14-1
Sawtooth Sweep Generator
Q920 and Q922 forma Miller integrator circuit. When
the current through the Sweep Disconnect Amplifier Q904
is interrupted, timing capacitance C, begins to discharge
through timing resistor R
t
. The timing resistor and
capacitance are selected by the A TIME/DIV switch to
provide the various sweep rates listed on the instrument
front panel. The output signal at the collector of Q922 is a
negative-going sawtooth voltage waveform.
Sweep Start Amplifier
Just before the sweep starts to run down, the levels at
the bases of Q914 are approximately equal When the
sweep starts to run down, the base of Q914B goes
negative, which increases the forward bias on CR914B.
This in turn decreases the forward bias on CR914A, which
very shortly after the start of the sweep, becomes reverse
biased to interrupt the current through Q914A. The
circuit remains in this condition until after the sweep
retrace is complete.
When the circuit returns to
quiescence, Q914A begins to conduct through R904. This
sets the current through Q904 which in turn establishes
the DC level starting point for the sweep.
Output Buffer Amplifier
Q940 and Q956 form the Output Buffer Amplifier. Q940
is an emitter follower and Q956 is a common-base
amplifier whose emitter is current-driven by the signal.
The Output Buffer Amplifier provides the output sawtooth
signal current to the Horizontal Amplifier and provides a
measure of isolation between the Sawtooth Generator and
the Horizontal Amplifier. Intensified Gain adjustment
R950 adjusts the gain of the stage to match the output
signal amplitude with that of the Non-Delaying Sweep
Generators.
The Delaylng Sweep Output Buffer Amplifier passes
the signal to the Horizontal Amplifier when the HORIZ
DISPLAY switch is in the A INTEN position and the
TIME/DIV switches are not in the X-Y position When the
TIME/DIV switches are in the X-Y position the anode of
CR956 is connected to +5 volts This sets the base of Q956
at a positive enough level to reverse bias Q956 and prevent
passage of the Delaying Sweep signal to the Horizontal
Amplifier. With the TIME/DIV switches not in the X-Y
position and the HORIZ DISPLAY switch in the A INTEN
position, R955 is connected to 8 volts (through Q1099 in
the Horizontal Display Switching circuit) and the anode of
CR956 is not connected to any voltage. This forward
biases CR955 and sets the base of Q956 at a DC level of
approximately +4.3 volts. Now Q956 is forward biased and
the Delaying Sweep signal is passed to the Horizontal
Amplifier.
Delaying Sweep End Difference Amplifier
Q944 and Q946 are connected as a voltage comparator
and generate the logic pulses that signal the end of sweep
and blank the CRT display at the end of the sweep. Prior to
the generation of a sawtooth voltage waveform by the
Delaying Sweep Generator, the base of Q944 is at an
approximate -1.6 volt level. The base of Q946 is held at
about –3 volts by the divider made up of R948 and R949.
Therefore, Q946
is reversed biased and not conducting
and Q944 is forward biased and is conducting. When the
sweep voltage at the emitter of Q940 begins to go in a
negative direction, the base of Q944 follows until the base
of Q944 goes more negative than the base of Q946. Q944
turns off and Q946 turns on, generating a positive pulse at
the collector of Q944 and a negative pulse at the collector
of Q946. The positive pulse at the collector of Q944 signals
the end of sweep and starts the holdoff period. The
negative pulse at the collector of Q946 signals the Z-Axis
Logic circuit to blank the CRT and prevent any further
display.
Q926A and Q926B are connected as a voltage com-
parator Q928 is a relatively constant current source for
Q926. Q938 is also connected as a voltage comparator
circuit and is used to improve the switching capabilities of
the stage. The reference voltage for the Delay Pickoff
Comparator stage is provided by DELAY TIME POSITION
control R930 U930 is an integrated circuit containing two
high-gain amplifier cells used in a feedback amplifier
configuration. They provide accurate fixed voltages
(determined by settings of Delay Start, R938, and Delay
Stop, R936) connected to the DELAY TIME POSITION
control to allow precise delay pickoff. The instrument is
calibrated so that the major dial divisions of the DELAY
TIME POSITION control correspond to major divisions of
horizontal deflection on the CRT graticule. For example, if
the DELAY TIME POSITION control is set to 5.00, the Non-
Delaying Sweep Generator is delayed five divisions of the
Delaying Sweep time before it can produce a sweep.
Delay Pickoff Comparator
The Delay Pickoff Comparator stage allows selection
of the amount of delay from the start of the Delaying
Sweep Generator before one of the Non-Delaying Sweep
Generators is turned on. The amount of delay available is
variable from 0.00 to 10.00 times the setting of the A
TIME/DIV switch. The sweep rate of the Delayed (non-
decaying) Sweep Generator is determined by the setting of
the B TIME/DIV switch.
3-18
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