Section 3—2205 Service
THEORY OF OPERATION
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SECTION ORGANIZATION
This section of the manual contains a general
summary of instrument functions followed by a
detailed description of each major circuit. A basic
block diagram, (Figure 9-4), and the schematic
diagrams are located in the tabbed Diagrams
section at the back of this manual. The black diaî™–
gram and schematic diagrams are used to show the
interconnections between parts of the circuitry and
to indicate circuit components.
The schematic diagram number associated with
each description is identified in the text and is Shown
on the block diagrams. For best understanding of
the circuit being described, refer to the appropriate
schematic diagram and the block diagram.
INTEGRATED CIRCUIT DESCRIPTIONS
Digital Logic Conventions
Digital logic circuits do many functions within the
instrument Functions and operation of the logic
circuits are represented by logic symbology and terî™–
minology. Most logic functions are described using
the positive-logic convention. Positive logic is a sysî™–
tem where the more positive of two levels is the
TRUE (or 1) state: the more negative level is the
FALSE (or 0) state. In this logic description, the
TRUE state is HI, and the FALSE state is LO. Voltage
levels for a HI or a LO state vary between specific
devices. For detailed device characteristics, refer to
the manufacturer's data book.
Linear Devices
The operation of individual linear integrated
circuit devices in this section use waveforms or
other techniques such as voltage measurement and
simplified diagrams to illustrate their circuit
operation.
GENERAL DESCRIPTIONW V H H M B Si«e W O T S H U ■m A tP
In the following functional description of the 2205
Oscilloscope, refer to the block diagram (Figure
9-4) located in the Diagrams section of this manual.
In Figure 9-4 the numbered diamond symbol in each
major block refers to the appropriate schematic
diagram number.
Vertical
Signals to be displayed on the crt (cathode-ray
tube) are applied to either or both the CH 1 or X
and the CH 2 OR Y input connectors. The signals
may be coupled to the attenuator either directly
(DC) or through an input-coupling capacitor (AC).
The inputs may also be disconnected, and the input
to the attenuators grounded, by switching to the
QND position of the input coupling switch, in the GND
position, the ac-coupling capacitor is allowed to
precnarge to the dc level present at the input
connector. This precharging prevents large trace
shifts of the display when switching from GND to AC
coupling. The Attenuators are switched by the
front-panel. VOLTS/DIV switches and scale the
applied signal level to obtain the desired display
amplitude.
The output signals from the Attenuators are apî™–
plied to the Vertical Preamplifiers for amplification.
The Channel 2 Preamplifier has additional circuitry,
permitting the operator to invert the Channel 2 disî™–
play on the cathode-ray tube (crt). Trigger pickoffs
in each channel supply a trigger signal to the Trigger
Amplifier when internal triggering is selected.
Input signals are selected for display by the
Channel Switching circuit under control of the front-
panel VERTICAL MODE switches. The output signal
from the Channel Switching circuit is applied to the
Vertical Output Amplifier.
3-1
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