Theory Of Operation; Block Diagram; Description - Tektronix 7844 Instruction Manual

THEORY OF OPERATION

This section of the manual decribes the circuitry used in the 7844/R7844 Oscilloscope. The description begins with a
discussion of the instrument, using the block diagram shown in the Diagrams section at the back of this manual. Next, each
circuit is described in detail with supporting illustrations, when appropriate, to show the relationship between the stages in
each major circuit. Detailed schematics of each circuit are located in the Diagrams section. Refer to these schematics through­
out the following circuit description for specific electrical values and relationships.
BLOCK DI AG RAM
The following discussion is provided to aid in understand­
ing the overall concept of the 7844/R7844 before the individ­
ual circuits are discussed in detail. A basic block diagram of
the 7844/R7844 is shown in the Diagrams section. Only the
basic interconnections between the individual blocks are
shown on this diagram. Numbers on blocks refer to major
circuits within the instrument. The number on each block
refers to the complete circuit diagram located at the rear of
the manual.

Description

Vertical signals to be displayed on the cathode ray tube
(crt) are applied to the Vertical Interface circuits from both
vertical plug-in compartments. The VERTICAL MODE
switch determines whether the signals from the LEFT VERT
or R IGHT VERT compartments are displayed by beam 1 or
beam 2. The selected vertical signals are amplified by the
Vertical Amplifier circuits to bring them to the level neces­
sary to drive the vertical deflection
Beam 2 Vertical Amplifier circuit also includes an input from
the Readout System to produce the vertical portion of the
alphanumeric readout display.
Horizontal signals for display on the crt are connected to
the Horizontal Interface circuits from both horizontal plug-in
compartments. The HORIZONTAL MODE switch deter­
mines whether the signals from the A HORIZ or B HORIZ
units are displayed by beam 1 or beam 2. The selected hori­
zontal signals are amplified by the Horizontal Amplifier cir­
cuits to provide horizontal deflection for the crt. The Beam 2
Horizontal Amplifier circuit also accepts an input signal from
the Readout System to produce the horizontal portion of the
alphanumeric readout display.
The Readout System provides alphanumeric display of
information encoded by the plug-in units. The readout dis­
\
play is written on the crt by beam 2 on a time-shared basis
REV J U N 1 981
INTRODUCTION
with the analog waveform display. The MODE switch cir­
cuits determine which plug-in units display readout informa­
tion. The Readout and Grat Ilium Control circuits contain the
controls necessary for the operation of the pulsed readout
and pulsed graticule illumination functions.
are connected to the Trigger Selector circuits. The Mode
Switch and Trigger Selector circuits direct trigger signals
from the LEFT VERT or R IGHT VERT units to the A HORIZ
or B HORIZ units.
circuits within this instrument and the plug-in units. These
control signals automatically determine the correct instru­
control settings, and 7844/R7844 control settings.
plates of the crt. The
Section
The internal trigger signals from the vertical plug-in units
The Logic circuit develops control signals for use in other
ment operation in relation to the plug-in units, plug-in unit
The CRT circuit contains the control circuits necessary
for operation of the crt. The Z-Axis Amplifiers for beams 1
and 2 provide the drive signal to control the intenSity level of
the crt display.
The Calibrator circuit produces a 1 kHz square-wave sig­
nal that can be used to check the calibration of this instru­
ment and the compensation of probes. The calibrator signal
is available as a voltage at the CALIBRATOR connector or
as a current through the 40 mA current loop (optional cur­
rent loop adapter necessary for the R7844).
The Signals-Out circuits process signals from the plug-in
units for rear-panel output. Input signals are coupled to the
Signals-Out circuits for use by the 7844/R7844 or the plug­
in units.
The Converter/Rectifiers and Low-Voltage Regulator cir­
cuits provide the power necessary to operate this instru-
Service
3-7844/R7844
3-1