Tektronix 7834

Left and Right Trigger Preamplifiers
The operation of the Left and Right Trigger Preamplifiers is
similar . Therefore only a discussion of the Left Trigger Pre-
amplifier is given .
The Left Trigger Preamplifier U520 operates as a switching
amplifier . Trigger signals from the LEFT VERT compart-
ment are connected to the input pins 1 and 13 (U520) . The
logic levels applied to pins 11 and 12, determine if the trig-
ger signal is coupled from the input to the output (pins 9
and 5) or is terminated within the stage . Table 3-2 shows
the logic level combinations applied to pins 11 and 12 of
both U520 and U580, with all combinations of the A
TRIGGER SOURCE switch and the VERTICAL MODE
switch . When pin 11 is HI and pin 12 is LO, trigger signals
are coupled through the stage . When pin 1 1 is LO and pin 12
is HI,
signals are terminated within the stage .
A Trigger Output Amplifier
The A Trigger
Output Amplifier provides the internal trigger
signal
to the
A
HO RIZ compartment . Transistors 0585 and
Q598 are connected as a paraphase amplifier . The DC Center
adjustment
R586 balances the emitter current of Q588 and
Q598 for equal do output levels . Gain adjustment R589 sets
the emitter degeneration of Q588 and Q598 to adjust the
gain of the
A
Trigger Output Amplifier . Components R596
and C596 are selected for optimum amplifier bandwidth .
The
output impedance of this stage is 100 ohms differen-
tially, determined primarily by R584 and R594 .
Vertical Signal Out Amplifier
The Vertical Signal Out Amplifier provides the signal to the
VERT SIG OUT connector, located on the rear panel . Tran-
sistors Q548 and Q558 are connected
as a
push-pull
to
single-phase converter . The DC Center adjustment, R547,
sets the emitter current of Q548 and Q558 which deter-
mines the quiescent do output voltage at J548 . The source
of the output signal is determined by the A TRIGGER
SOURCE switch and the VERTICAL MODE switch as
shown in Table 3-2 .
B TRIGGER SELECTOR
The B Trigger Selector circuit determines the source of the
internal triggering signals connected to the B HORIZ plug-
in compartment . Figure 3-24 shows a detailed block
diagram of the B Trigger Selector circuit . A schematic of
the B Trigger Selector circuit is shown on diagram 6, at the
rear
of
this
manual
.
B Trigger Channel Switch
The B Trigger Channel Switch provides control signals for
the Left and Right Trigger Preamplifier stages . The front-
panel B TRIGGER SOURCE switch (S352) provides
the
control signals to operate the B Trigger
Channel
Switch
.
When the B TRIGGER SOURCE is set to
LEFT,
the
B
Trigger Channel switch allows the Left Trigger Preamplifier
to pass trigger signals from the LEFT VERT plug-in com-
partment to the B Trigger Output Amplifier . When the
B TRIGGER SOURCE switch is set to RIGHT, the B
Trigger Channel Switch allows the Right Trigger
Preampli-
fier to pass trigger signals from the RIGHT VERT plug-in
compartment to the B Trigger Output Amplifier . When the
B TRIGGER SOURCE switch is set to VERT MODE, the
B Trigger Channel Switch allows the Left and Right Trigger
Preamplifier stages to pass trigger signals from the LEFT
and RIGHT VERT plug-in compartments to the B Trigger
Output Amplifier .
Table 3-3 shows the input and output conditions of
the B
Trigger Channel Switch, for each combination of the
B
TRIGGER SOURCE switch and the VERTICAL MODE
switch . Notice that only the B TRIGGER SOURCE switch
controls the output to U620 and U680 when in the LEFT
or RIGHT VERT positions . Also, notice that the
VERTI-
CAL MODE switch determines the output when
the B
TRIGGER SOURCE switch is in the
VER'TMODE position .
Left and Right Trigger Preamplifiers
Theory of Operation-7834
The operation of the Left and Right Trigger Preamplifiers is
similar . Therefore, only a discussion of the Left Trigger
Preamplifier is given .
The Left Trigger Preamplifier U620 operates as a
switching
amplifier . Trigger signals from the LEFT VERT compart-
ment are connected to the input pins 1 and 13 (U620) . The
logic levels applied
to pins 11 and 12,
determine
if
the trig-
ger signal
is coupled from the input to the output (pins 9
and 5) or is
terminated
within
the stage
. Table
3-3
shows
the logic level combinations applied
to
pins 11 and 12 of
both U620 and U680, with all combinations of the B TRIG-
GER SOURCE switch and the VERTICAL MODE SWITCH .
When pin 11
is
HI and pin
12 is LO,
trigger signals are
coupled through the
stage
. When pin 11
is LO and pin
12 is
HI, trigger signals are terminated within the stage .
B Trigger Output Amplifier
The B Trigger Output Amplifier provides the internal trigger
signal to the B HORIZ compartment . Transistors Q688 and
0698 are connected as a paraphase amplifier . The DC Cen-
ter adjustment R686 balances the emitter current of Q688
and Q698 for equal
do output levels . Gain adjustment R689
sets the emitter degeneration
of Q688 and Q698 to adjust
the gain of the B Trigger Output Amplifier . Components
R696 and C696 are selected for optimum amplifier band-
width .
The output impedance of this stage is 100 ohms
differentially,
determined primarily by R684 and R694 .
3- 3
1