Tektronix 5441 Instruction Manual page 37

Section 3-5441lR5441
THEORY OF OPERATION
INTRODUCTION
This section of the manual contains a description of the Refer to the appropriate diagrams in the Diagrams and
circuitry used in the 5441lR5441 oscilloscope. Individual de- Circuit Board Illustrations section of this manual while read-
scriptions are separated into the following parts: Main Inter-
ing the circuit descriptions.
face, Vertical Amplifier, Horizontal Amplifier, 2-Axis
Amplifier & CRT Circuit, Storage Circuit, Low Voltage Pow-
er Supply, Calibrator, and Readout System.
INTERFACE
The interface circuit provides an interconnection of sig-
nals, logic levels, and power-supply voltages between plug-
in units and the oscilloscope mainframe. It incorporates
circuits that determine the vertical display mode and amplify
the vertical and horizontal display signals. Functions of in-
terconnections not discussed are labeled on the interface
diagram.
Chop Oscillator
The chop oscillator produces a 200 kHz square-wave
signal for chopping between vertical plug-ins and amplifier
channels within the plug-ins. This multivibrator circuit con-
sists of U770A, U770B, and associated passive compo-
nents. When the multivibrator receives a chop actuate level
(+5 V), it free-runs at a 100 kHz rate. (The chop actuate
level is routed through the vertical plug-ins to the time-base
unit, and is present at contact A20 of J630 when a multi-
trace display is required and the time-base Display switch is
set to Chop.) The chop actuate level also disables (2770,
locking out alternate-drive pulses. The multivibrator has two
outputs; one is sent through buffers to the divider circuit as
a timing signal, and the other is sent to the U770D and
U770C circuit to blank the chop-switching transients.
Divider Circuit
transition, which can come from either the chop oscillator or
from the time-base plug-in unit via grounded-base amplifier
(2770. The chop oscillator input results in chopped-mode
vertical switching. The input from the time-base unit coin-
cides with the end of each sweep, and results in alternate-
mode vertical switching. The output from the divide-by-two
portion of the divider circuit, U780A, is sent via contacts
821 of J610 and J620 to the channel-switching circuits in-
corporated within multi-trace vertical plug-in units. The out-
puts from the divide-by-four portion of the divider circuit,
U780B, are used for plug-in switching; one output is sent to
pin 4 of the vertical integrated switching circuit to produce
plug-in switching, and the other output is sent via contct
821 of J630 to produce dual-sweep switching in dual-time-
base units. The vertical mode switching sequence and some
of the display combination possibilities are fully discussed in
the Operating Information section of this manual.
Vertical Amplifier and Vertical Integrated Switching
Circuit
Emitter followers (2600, Q604, (2610, and Q614 provide
a high-impedance input to the vertical amplifier and vertical
integrated switching circuit, U620. The vertical amplifier in-
put resistance for the oscilloscope mainframe is determined
by R601, R605, R611, and R615.
The divider circuit produces the display switching signal
for both the Alternate and Chopped switching modes. This
The vertical integrated switching circuit permits only one
circuit is composed of U780, and its discrete passive com- of the two vertical plug-in signals to pass to the vertical
ponents, which is connected as a pair of JK flip-flops. Each output amplifier, the level at pin 4 of U620 determines the
flip-flop is a divide-by-two counter; the first one driving the plug-in signal that is passed to the vertical amplifier. When
second. The divider circuit is activated by a negative-going the Display On pushbutton on the right-hand vertical plug-in
REV MAY 1982
3- 1