Theory
of Operation
—
7T11A
The minimum hold-off
time on the three real-time ranges
is approximately
equal
to the sum of the two 1/2 hold-off
intervals (a total
of about 2 ms). At the slower real-time
sweep
rates or when time
positioning is used, hold-off time
increases and the maximum
triggering
rate therefore
decreases.
SEQUENTIAL EQUIVALENT-TIME
SAMPLING
Additional
Circuits Required
Figure
3-8 shows a simplified
block diagram
of circuits
required
for
sequential equivalent-time operation of
the
7T11A. Comparison
of
Figure 3-8 with the real-time block
diagram
shown
in
Figure 3-2 shows that the Reset Compar
ator
and
Real-Time Multivibrator are not used during equiv
alent-time operation.
Additional circuits (shown in
Figure 3-8), required during
sequential
operation
are: Slewing
Ramp, Slewing Compara
tor, Slow
Ramp Generator,
Slow Ramp Inverter, Dot Posi
tion
Comparator,
and Dot Position Memory.
Slewing
Ramp.
The
Slewing
Ramp is a fast ramp
that is
started
at
the
same time as the TTH ramp and runs negative
at the same rate. Its slope
is determined by which of the four
equivalent-time
Sweep Ranges is selected. The output of
the
Slewing Ramp is fed to one input of the Slewing Com
parator, where its voltage is compared to the inverted out
put
of the Slow Ramp
Generator.
Slow
Ramp.
The
Slow Ramp Generator output, after
passing through the Slow
Ramp Inverter, provides an input
reference
voltage to
the Slewing Comparator against which
the output of the Slewing
Ramp is compared.
The
output
of
the Slow Ramp Generator rises from 0
volts
to slightly more than +10 volts and is
then
reset by a
reset
multivibrator. After a short hold-off interval, a
nega
tive-going
output
of the HOMV is able
to again shut off the
reset
multivibrator,
permitting generation of another slow
ramp.
The
rate
of
rise
and therefore the time required to gener
ate
the
Slow Ramp is controlled by the SCAN conrol. On
equivalent-time
ranges and with REP SCAN selected, the
SCAN
control permits controlling
the
dot density of the
display.
Slow Ramp
Inverter.
The
Slow
Ramp Inverter inverts
the Slow
Ramp
output. The negative-going output of the
Inverter is
applied to
the Slewing Comparator.
The
TIME POSITION control introduces offset to the
Slow
Ramp Inverter input to compensate for the offset in
troduced into
the Horizontal Amplifier by the Time POSI
TION control. Unless
this is done
the TTH ramp could be
stopped
by
the comparator before
any change in voltage
appeared
at
the output of the
Horizontal Amplifier.
Slewing Comparator.
The purpose
of
the Slewing Com
parator is
to compare
the
output of the Slewing Ramp with
the output
of the Slow
Ramp Inverter. When these two in
puts to the comparator are equal, the comparator delivers
an output. The Slewing
Comparator output initiates the
strobe
pulses
that are delivered to the vertical unit
sampling
heads
and cause them to sample the input signals. The
Slewing
Comparator output also stops the negative-going
TTH
ramp. This stopped level is then amplified and read into
the Horizontal
Memory at 1/2 hold-off time.
Dot
Position Comparator and
Memory.
Factors
deter
mining
the timing and linearity of the CRT display are the
cleanliness
of the TTH Converter,
Horizontal Amplifier, Hori
zontal
Memory, and output circuits. The nonlinearities and
distortions
present
in the Slewing Ramp, Slewing Compara
tor, and Slow Ramp
circuits do not affect display timing and
linearity.
The
independence
of these two groups of circuits
cause
the
timing
of the output from the Slewing Comparator
to be
critical.
If the
Horizontal
Amplifier is set to a magnification ratio of
50, a 0.1
volt excursion
of the
TTH ramp
shows up as a
10
volt
excursion at the
output of the Horizontal Memory.
Also,
the Time
Position control can be set so that the TTH
Con
verter must go through
an excursion of 5 volts before the
Horizontal
Amplifier becomes operative. It is this situation
that makes
the
timing of
the Slewing Comparator output
very
critical.
Since
the timing
of the
Slewing Comparator output sets
the output level
of the TTH Converter, and since this firing is
dependent
upon the programmed level set by the Slewing
Ramp,
Slewing
Comparator, Slow Ramp, and Slow Ramp
Inverter, it is
easy to see that a few millivolts of program
ming
error can
cause
the TTH ramp to be stopped at a
level
corresponding
to
an off screen dot position.
The Dot
Posi
tion
Comparator and
Dot Position Memory are provided to
prevent this
programming error.
The
Dot Position Comparator
compares the
voltage from
the
Horizontal Memory (via the Output Amplifier) with the
Slow
Ramp voltage.
If
the Memory voltage is not at the
3-10
Summary of Contents for 7T11A
Page 10: ...7T11A Instruction Manual 7T11A Sampling Sweep Unit viii ...
Page 39: ...Theory of Operation 7T11A 3 11 ...
Page 44: ...Theory of Operation 7T11A Figure 3 11 7T11A Blanking Logic 3 16 ...
Page 47: ...Theory of Operation 7T11A Figure 3 14 Random mode block diagram 3 19 ...
Page 179: ...y TRIGGER INPUT HF Sync Selected HF Sync Selected ...
Page 180: ...THIA SAMPLING SWEEP UNIT 6176 127 ...
Page 181: ...TRIGGER INPUT J TRIGGER INPUT 6 76 127 ...
Page 182: ...7T11A A3 TRIGGER BOARD Figure 8 3 A3 Trigger circuit ...
Page 183: ......
Page 185: ...Ext Trig ...
Page 186: ......
Page 187: ......
Page 189: ......
Page 191: ...Time position CW SEQUENTIAL OV Ext Trig Time position CW RANDOM ...
Page 192: ......
Page 193: ...TIME TO HEIGHT CONVERTER 176 12 5 TIME TO HEIGHT CONVERTER s 9 ...
Page 194: ...7T11A A1 LOGIC BOARD ...
Page 195: ......
Page 197: ...1000 Ω resistor between pins 17 18 of J641 ...
Page 198: ...NOTfcS UEADLE55 CAPACITOR l FOR DECOUPLING NETWORKS SEE H THIA SAMPLING SWEEP UNIT GITG I3Ö ...
Page 199: ......
Page 200: ...7T11A A4 INTERFACE BOARD Figure 8 6 A4 lnterface circuit ...
Page 201: ...b 8 6 A4 lnterface circuit board assembly ...
Page 203: ......
Page 204: ......
Page 205: ......
Page 206: ...5 ns DIV 5 ns DIV 5 ns DIV 5 ns DIV Ext Trig 5 ns DIV ...
Page 207: ......
Page 208: ......
Page 209: ...Ext Trig ...
Page 210: ......
Page 211: ......
Page 212: ......
Page 213: ......
Page 214: ......
Page 215: ... 7TII SAMPLING SWEEP UNIT W7G 135 ...
Page 216: ...W7G 35 TIMING SWITCHES TIMING SWITCHES ...
Page 218: ...OUTPUT CONNECTORS 136 OUTPUT CONNECTORS 0 ...
Page 219: ...PARTIAL A4 INTERFACE OARD Gl7 i I37 7T11A SAMPLING SWEEP UNIT ...
Page 220: ... 137 VOLTAGE DISTRIBUTION DECOUPLING VOLTAGE DISTRIBUTION DECOUPLING H ...
Page 221: ... 174 136 1T11R SAMPLING SWEEP UNIT ...
Page 222: ...FRONT PANEL SWITCHING ...
Page 223: ...TP884 TP658 Figure 8 7 Location of Logic adjustments A2 5 im R ...
Page 231: ...12 ...
Page 232: ...FIG 1 EXPLODED VIEW 7T11A ...
Page 234: ...F IG 2 ACCESSORIES 7T11A ...