Tektronix 5110, Instruction Manual

Page: 59 / 128

Section 5—5110
CIRCUIT DESCRIPTION
This section of the manual contains adescription of the
circuitry used in the oscilloscope. Individual descriptions
are separated into the following parts: Block Diagram,
Interface, Auxiliary Board, Vertical and Horizontal Deflec­
tion Amplifiers, CRT Circuit, and last, Low-Voltage Power
Supply and Calibrator. Refer to the appropriate diagrams
in the Diagrams section of this manual while reading the
circuit descriptions.
BLOCK DIAGRAM DESCRIPTION
Vertical signals to be displayed on the cathode-ray tube
are applied through the Interface circuit to the Auxiliary
board from both vertical plug-in compartments. The
Interface circuit determines whether the signal from the
left or right vertical unit is displayed. The Vertical Amplifier
circuit provides intermediate amplification between the
vertical plug-in units and the Vertical Deflection Amplifier.
Time-base and external signals for horizontal display
on the crt are connected to the Interface circuit from the
horizontal plug-in compartment. The Horizontal Amplifier
circuit provides intermediate amplification between the
horizontal plug-in unit and the Horizontal Deflection
Amplifier.
Additionally, the Interface circuit provides an inter­
connection
of logic levels, time-base triggering signals,
display-related signals, and power-supply voltages
between the plug-in units and the oscilloscope.
The Vertical and Horizontal Deflection Amplifiers
provide final amplification for the signals from the plug-in
units. They produce push-putt outputs suitable to drive the
crt vertical and horizontal deflection plates. Beam-finding
circuitry is incorporated to limit the display within the
screen area when the front-panel BEAM FINDER button is
pressed.
The CRT circuit produces the high voltage (about —3.4
kilovolts) and contains the controls necessary for opera­
tion of the cathode-ray tube. The CRT circuit also contains
the Z-Axis Amplifier, which provides the drive signal to
control the intensity level of the display.
The Low-Voltage Power Supply Regulator circuits
provide the voltage necessary for operation of the os­
cilloscope system. These voltages are connected to all
circuits within the instrument. Also included in this circuit
is the Calibrator, which produces a square wave output
signal at the front panel. The output has an accurate
amplitude which can be used to check vertical deflection
factor accuracy and probe compensation.
INTERFACE
The Interface circuit provides an interconnection of
signals, logic levels, and power-supply voltages between
plug-in units and the oscilloscope
mainframe. It incor­
porates circuits that determine the vertical display mode
and amplify the vertical and horizontal display signals.
Functions of interconnections not discussed are labelled
on the Interface diagram.
Clock Generator
The Clock Generator stage produces a 200-kilohertz
timing signal (clock) for chopping between vertical plug­
ins and amplifier channels within the plug-ins. This circuit
consists of Q620, Q626, and their associated passive
components, which are connected as a multivibrator.
When the multivibrator receives a chop actuate level (+5
volts), it free runs at a 200-kilohertz rate. (The chop
actuate level is routed through the vertical plug-ins to the
time-base unit, and is present at contact A20
of J603 when
a multi-trace display is required and the time-base Display
switch is set to Chop.) The chop actuate level also disables
Q630, locking out alternate-drive pulses. The Clock
Generator
has two outputs; one is sent to the Countdown
circuit as a timing signal, and the other is sent to the crt
circuit to blank the chop-switching transients.
Countdown Circuit
The Countdown circuit produces the display switching
signal for both the Alternate and Chopped switching
modes. This circuit is composed of U640 and its discrete
passive components, which are connected as a pair
of RS
flip-flops.
Each flip-flop is a divide-by-two counter, and
the first one drives the second. The Countdown circuit is
activated by a negative-going transition, which can come
from either the Clock Generator or from the time-base
plug-in unit via grounded-base amplifier Q630. The Clock
Generator input results in chopped-mode vertical
switching. The input from the time-base unit coincides
with the end of each sweep, and results in alternate-mode
vertical
switching. The output from the divide-by-two
portion of the Countdown circuit (U640A-U640B) is sent
via
contacts B21 of J601 and J602 to the channel­
switching circuits Incorporated within dual-trace vertical
plug-in units. The outputs from the divide-by-four portion
of the Countdown circuit (U640C-U640D) are used for
plug-in switching; one output is sent to contact A15 of
J604 to produce plug-in switching on the single-beam-
display auxiliary board, and the other output is sent via
contact B21 of J603 to produce dual-sweep switching in
dual time-base units. The vertical mode switching se­
quence and some of the display combination possibilities
are fully
discussed under General Operating Information
in the Operating Instructions section of this manual.
5-1