Slope Comparator; Output Stage; Trigger Generator; Trigger Pulse Generator - Tektronix 7B70 Time Base Instruction Manual

Circuit Description-7B7O (SN B205000 and Up)
sensing network
is
the same as that described for the peak
positive sensing network. The output at the source of 0255
is applied to the bottom of LEVEL control R146A as a
negative-going voltage which represents the peak negative
value of the signal input.
MODE, COUPLING and SOURCE controls are included
in the output stage of the Peak Detector.
Slope Comparator
The Slope Comparator is the electronic equivalent of a
double-pole double-throw switch. With the SLOPE switch
set for positive slope triggering, 0158-0159 are on and
0161-0168-0169 are off. For negative slope triggering,
0161-0168-0169 are on and 0158-0159 are off. R155
adjusts the negative P-P AUTO triggering when the LEVEL/
SLOPE control is set to the negative slope.
Output Stage
The output of the slope comparator is applied through
the Output Stage to the trigger generator circuit. Diodes
CR181 and CR182 limit the push-pull output of the trigger
amplifier to about one volt peak-to-peak.
TRIGGER GENERATOR
Trigger Pulse Generator
The Trigger Pulse Generator (see Fig. 3-3) shapes the
output of the Trigger Amplifier to provide a trigger pulse
with a fast leading edge. Tunnel diode VR304 is quiescently
in its low-voltage state. The signal from the Trigger Ampli-
fier switches it to i t s high-voltage state causing a negative-
going fast rise pulse at the base of 0317 and a positive-
going pulse at the base of 0309. The output of the Trigger
Pulse Generator, at ,the collector of 031 7, is a positive-
going fast rise pulse which is applied to the Sweep Gate
Stage. The output at the collector of 0309 is a negative-
going pulse which is applied to the bright-line Auto circuit.
VR304 reverts back to its low-voltage state when the signal
from the Trigger Amplifier decreases sufficiently. VR304
runs at the repetition rate of the input signal.
Sweep Gate Stage
The Sweep Gate Stage produces a negative-going step to
start the Sweep Generator and a positive gate for use in the
osci Iloscope.
The positive-going pulse from the Trigger Pulse Genera-
tor enables CR319, opening an additional current path for
Fig. 3-3. Simplified block diagram of Trigger Generator circuit.
Scans by ArtekMedia
Q
2006
0 3 7 7
SWEEP
GATE
DELAY MODE CONTROL
-
EMITTER SWEEP
7
+ -
FOLLOWER
-
-
GATE
TO
OSClL LOSCOPE
F R O M
-
TRIGGER
AMPLIFIER
F
-
TRIGGER PULSE
GENERATOR
V R 3 0 4 , 0 3 0 9 , 0 3 1 7
-+
SWEEPGATE
-
:
SWEEP RESET
+
G
.
-+-
BRIGHT
LINE AUTO
0 3 3 1 , 0 3 3 8 , 0 3 3 9
D R I V E R
0 3 4 6 , 0 3 5 0
+5
v
(
h
SWEEP
GENERATOR
S273
/
/
/
!I
MULTIVIBRATOR
0 3 6 0 , 0 3 6 8
VR358
-
TRIGGERED
SWEEP START
.
L
-
F
T O
- :
\
F R O M SWEEP
r +
GENERATOR
HOLDOFF STAGE
0 3 2 6 , 0 3 2 8
VR322