Horizontal System - Tektronix 1S1 Instruction Manual

Circuit Description – Type 1S1
displayed sample, the amount of attenuation the feedback
loop determines the gain of the display by setting the ratio
between the voltage level at the memory output and that
at the sampling gate. For correct response, the feedback
following each sample must be of the amplitude required
to bring the level at the sampling gate up to the level of
the input signal during the previous sampling instant. When
it is adjusted, the loop is said to have a gain of 1.
As the feedback signal is decreased to increase the dis-
play gain, amplification of the error-correction sample must
also be increased to keep the loop gain at 1. Since the
gain of the amplifiers is fixed, the additional amplification
is produced by allowing more of the error-correction signal
to pass through R58-R60 to the ac amplifier. The error-
correction attenuation caused by R58-R60, therefore, must
decrease as the feedback attenuation is increased. These
two attenuators are operated simultaneously by the front-
panel mVOLTS/CM switch, SW60.
Output Cathode Followers
The 600 mv/cm output from the memory circuit is applied
through two divider networks to the grid of cathode-fol-
lower V183A. This divider action reduces the 600 mv/cm to
the 100mv/cm required by the oscilloscope vertical ampli-
fier. The mVoIts/Cm VARIABLE control (R165) is one of the
resistors making up the attenuators. Due to its voltage
division with R167 and R168, the VARIABLE control can
increase the display amplitude by a factor of 4. Since this
control occurs in the circuit following the VERT OUTPUT
jack and the feedback loop, it does not affect the output
voltage at either the VERT OUTPUT jack or the OFFSET
OUTPUT jack.
During retrace of the staircase, a blanking pulse is applied
from the retrace blanking amplifier in the staircase circuit
through D175 and R177 to the grid of V183A. This negative-
going gate pulse moves the trace off screen (in a negative
direction) while the crt beam is returning to the left edge
of the screen. During the staircase, D175 is reverse biased,
disconnecting the blanking amplifier from the vertical system.
Vertical positioning cathode-follower
positioning of the display by changing the dc voltage ap-
plied through pin 3 of the interconnecting plug to one side
of the vertical amplifier in the oscilloscope. The output volt-
age from V183B is adjusted by the front-panel VERT POSI-
TION control and by the internal POSITION RANGE ad-
justment (R194). The positioning range produced by the
VERT POSITION control is 10cm or more on the crt screen.

HORIZONTAL SYSTEM

The horizontal system of the Type 1S1 provides the hori-
zontal deflection voltage for the display oscilloscope and
simultaneously controls the time at which the vertical system
samples the input signal. The horizontal system utilizes a
tunnel-diode trigger circuit possessing wide bandwidth ca-
pabilities, a Miller-type staircase generator for generating
the equivalent-time sweep, and a fast ramp circuit that
develops the real-time time base for operating the sampling
system. Triggering up to 1 Gc is provided by the tunnel
diode trigger circuit.
3-8
Cycle of Operation
the unit is received either from the trigger takeoff in the
vertical system or from the front-panel EXT TRIG connector.
The trigger circuit input recognizes either positive-going
or negative-going triggering signals, depending on the set-
ting of the TRIGGER SOURCE switch. After recognizing an
excursion of the input signal, the trigger circuit produces an
output pulse that unclamps the fast ramp generator and
permits it to start the fast rundown. The trigger holdoff
multivibrator then prevents another trigger recognition from
being made until after the fast ramp has run down and been
reset.
where it is compared to the staircase feedback voltage
received through the staircase inverted circuit. When the fast
ramp voltage becomes equal to the existing level of the
staircase feedback, the comparator produces an output
pulse which is sent to the vertical system as a sampling-
drive pulse, and to the staircase generator as unlock and
advance pulses. Since the voltage ramp is linear, the dc
level of the ramp at the time of comparison is proportional
to the amount of time that it takes the ramp to run down
to the staircase feedback level. Thus, the horizontal position
of each dot on the crt screen is proportional to the real
time duration between triggering and the taking of a sample.
The staircase-advance pulse, applied through the staircase
driver, pulses the staircase circuit, causing the output level
to advance one step.
be displayed. Each time the trigger circuit makes a recogni-
tion, the fast ramp makes a rundown excursion, the compara-
tor produces an output pulse and the staircase generator
steps up another increment. The resulting staircase output
is applied by way of the front-panel HORIZ OUTPUT jack
to the oscilloscope horizontal amplifier to produce the
equivalent-time sweep and also is fed back to the staircase
inverter circuit to provide the comparison voltage that de-
termines the time a sample is taken and displayed. The size
of the staircase voltage increments, set by the SAMPLES/CM
control, determines the equivalent-time spacing between
samples (dot density). For example, if the size of the steps
V183B provides
between samples is set so that there are 1000 samples per
sweep, the fast ramp will run down 1000 times while the
staircase output moves the crt spot across the screen one
time.
the SWEEP LENGTH control), it resets the sweep-gating
multivibrator, causing the Miller capacitor to discharge and
the retrace blanking amplifier to deflect the crt beam off
screen during retrace of the beam. The sweep-gating mul-
tivibrator is then ready to permit a new staircase to start
when the next sweep-unlock and staircase-advance pulses
are received.
HORIZ or MAN position, the staircase voltage is not used. In-
stead, an external ly-derived deflection voltage or an internal
dc voltage is applied through the staircase generator
and the HORIZ OUTPUT jack to the oscilloscope horizontal
amplifier. The display timing is the some as when the stair-
case sweep is used, but the scanning rate is set by the
external signal or the dc level change. In either case, the
The input triggering signal that starts the operation of
The fast ramp voltage is applied to the comparator circuit
One trigger recognition must be made for each dot to
When the staircase output reaches a certain value (set by
When the DISPLAY MODE switch is set to either the EXT