Tektronix T922 User Manual

Transistor U2126E is a high gain feedback
amplifier . To
achieve stable triggering on
TV signals, the LEVEL control must
be set at a point that will
allow the sync pulses to appear within the
dynamic range of the amplifier .
The sync separator
circuit consists of Q2174 and associated
circuitry
.
It
processes sync-positive pulses when the SLOPE
switch is in
the +OUT position and sync-negative pulses in the
-IN position . Transistor Q2174 produces large positive-going
pulses from negative-going sync signals at the collector of
U2126E .
In the TV field mode (SEC/DIV switch set
for .1 ms or slower),
Q2176 is saturated
(since base is grounded), and the integrator
(composed of
C2174, C2176, R2174, and R2176) is switched into
the circuit (effectively connected to +8 volts through saturated
Q2176) . The integrator filters out the horizontal sync pulses,
leaving only the integrated vertical sync pulses, which trigger the
TV Schmitt trigger U2156B and U2156C .
In the TV line mode (SEC/DIV switch set for 50 Ns or faster) .
Q2176
is turned off (base open), disconnecting C2174 and C2176
from +8 volts . Capacitors C2174 and C2176 no longer integrate
the pulses, thus allowing both the horizontal and
vertical
sync
pulses to pass through to the TV Schmitt trigger .
VII . 2
SCHMITT TRIGGERS
The Schmitt trigger for the NORM and AUTO triggering modes
consists of U2156A,U2156B, and associated circuitry .
Hysteresis
of this trigger circuit is determined by R2152,
R2153, and R2147 .
The Schmitt trigger for the TV triggering mode is U2156B,
U2156C,U2156D, and associated circuitry . Resistors R2154 and
R2178 determine the sensitivity .
When the MODE switch S2150 is in AUTO or
NORM, +8 volts is
applied
to R2156
which causes pin 1 of U2156Ato go HI, enabling
Schmitt trigger U2156A-U2156B . At the same time, pins 12 and 13
of U2156D are also HI disabling Schmitt trigger U2156C-U2156B .
A trigger signal from U2126D triggers Schmitt trigger U2156A-
U2156B to produce a logic trigger signal at
pin
6 of
U2156B .
When the MODE
switch S2150 is in TV, +8 volts is removed
from R2156 and pin 1 of U2156A is LO, disabling Schmitt trigger
U2156A-U2156B
. Pins 12 and 13 of U2156D are LO, enabling
Schmitt trigger U2156C-U2156B . The trigger signal from the TV
sync separator triggers Schmitt trigger U2156C-U2156B to
produce a logic trigger signal at pin 6 of U2156B .

Tektronix T922 Specifications

General

Brand	Tektronix
Model	T922
Category	Test Equipment
Language	English