Tektronix 7834 User Manual

Theory of Operation--7834
CHOPPED BLANKING
INHIBIT AND READOUT
BLANKING INHIBIT
CHOPPED BLANKING
INHIBIT, READOUT
BLANKING INHIBIT,
AND INTENSITY
LIMITING
AUXILIARY Z-AXIS
AGATE --- ---------

---~--
MAIN FRAME CHANNEL
SWITCH SIGNAL
A INTENSITY ----r--m---- ----~-
3- 1 6
8
Z-AXIS
SIGNAL
INTENSITY LIMITING
AND Z-AXIS LEVEL -
ADJUSTMENT

(1195-8) 1988-33
Figure 3-8 . Input and output pins for Z-Axis Logic IC (U4494)
.
Intensity limiting is provided for high crt beam currents at
slow sweep rates and
X-Y
operation
by the Intensity Limit
input . Quiescently,
04474 is reverse biased ; resistors R4485,
R4481, and R4474 establish
the current at pins 6 and 10 of
U4494 . When the Intensity Limit input
is connected to
ground, in the plug-in
units for slow sweep rates and ampli-
fire operation, the emitter of 04474 is grounded through
CR4472 . Transistor 04474 takes current from pins 6 and
10 of U4494 to limit the output current from this stage .
The A INTENSITY control sets the output current
level
when the
A
Gate at pin 14 is
H I
and the
main frame channel
switch signal (Display
B)
at pin 15
is LO . Whenever the A
Gate level goes LO indicating that the A sweep is
complete
or the Display B goes HI indicating that the
B
sweep is
being displayed, the
A
IN
- rENSITY
current
is blocked . The
current from the A
INTENSITY
control is connected to
pin 16 through
R4496
.
In the delayed mode, current is added to the A INTENSITY
current during the A-sweep time to intensify a portion of
the trace . This intensified portion is coincident with the
B-sweep time to provide an indication of which portion of
the A sweep is displayed in the delayed mode . The A inten-
sified current is supplied to pin 2 of U4494 from the A
INTENSITY control through R4496 . With this configura-
tion, the intensified
current
increases as
the A INTENSITY
control setting is advanced to provide a proportional inten-
sity
increase in the intensified zone as the overall A-sweep
intensity
increases
.
Therefore, the
intensified
zone
is
more
readily visible at high intensity
levels . The intensified current
is added to the A INTENSITY
current to produce an inten-
sified zone on the A sweep under
the following conditions :
H I A Gate level at pin
14, LO Display B at pin 15, H I B
Gate level at pin
4, and HI Delay Mode Control Out level at
pin 5 .
The B INTENSITY control
determines the output current
when the
B
Gate
level
at
pin 4 and the Display B at pin 15
are both HI . The
current from the B INTENSITY control is
connected to the
Z-Axis Logic stage through R4498 .
The current level established by the intensity
controls can
be altered by the Auxiliary Z-Axis
current level at pin 9 .
The current at this pin can come
from the Z-AXIS INPUT
connector on the rear panel
(see diagram 3) or from any of
the plug-in
compartments . This current either increases or
decreases (depending
on polarity) the output current to
modulate the intensity
of the display . Input from the
Z-AXIS
INPUT connector allows the trace to be modulated
by external
signals . The Auxiliary Z-Axis inputs from the
plug-in compartments
allow special-purpose plug-in units to
modulate the display
intensity . Diodes CR4473 and
CR4474
limit the maximum
voltage change at pin 9 to about + and
--0 .6 volt to protect
the Z-Axis Logic stage if an excessive
voltage is applied to the Z AXIS INPUT connector
.
Figure 3-9A shows a
logic diagram of the Z-Axis Logic stage
.
Notice the current-driven inputs as indicated by
the current
generator symbols at the associated inputs .
An input/output
table for the Z-Axis Logic stage is given in Figure 3-9B
.
Horizontal
Binary
The Horizontal
Binary stage produces the Main Frame
Channel Switch
Signal (Display B) to determine which
hori-
zontal
unit provides the sweep display on the crt .
When this
level is HI, the B HORIZ unit is displayed
; when it is LO,
the A HORIZ unit is displayed
.
The Display B signal is used in the following stages
within
the Logic circuit : Horizontal Logic (A and B Sweep
Inhi-
bit), Z-Axis Logic, Vertical Binary, and Trace
Separation .
In addition, it is connected to the following
circuits else-
where in the instrument to indicate
which horizontal unit
is to be displayed : Main Interface (A
and B HORIZ plug-in
compartments), Horizontal Interface (for
horizontal channel
selection), and the Auto Focus
Amplifier .
Figure 3-10 identifies the
function of the input pins for this
stage . Notice (on Logic diagram
4) that the levels at pins 3,
4, 7, and 10 of
U4358 are determined by the HOR IZON-
TAL MODE switch . This switch indicates which horizontal
mode has been selected by
providing a HI output level on
only one of four output lines ; the
remaining lines are LO .

Tektronix 7834 Specifications

General

Brand	Tektronix
Model	7834
Category	Test Equipment
Language	English