Tektronix 2230, Руководство по обслуживанию

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Section 3— 2230 Service
THEORY OF OPERATION
SECTION ORGANIZATION
This section contains a functional description of the
2230 Digital Storage Oscilloscope. The discussion begins
with a summary of instrument functions. Following the
general description, each major circuit is explained in
detail. Functional block diagrams and schematic diagrams
are used to show the interconnections between parts of
the circuitry, to indicate circuit components, and to identify
interrelationships with the front-panel controls.
Schematic diagrams and’ the overall block diagrams are
located in the tabbed “ Diagrams" section at the back of
this manual. The schematic diagram associated with each
description is identified in the text and indicated on the tab
of the appropriate foldout page by a numbered diamond
symbol. For best understanding of the circuit being
described, refer to both the appropriate schematic diagram
and the functional block diagram.
INTEGRATED CIRCUIT
DESCRIPTIONS
Digital Logic Conventions
Digital logic circuits perform many functions within the
instrument. Functions and operation of the logic circuits
are represented by logic symbology and terminology. Most
logic functions are described using the positive-logic con­
vention. Positive logic is a system 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. The specific
voltages which constitute a HI or a LO state vary between
specific devices. For specific device characteristics, refer
to the manufacturer's data book.
Linear Devices
The operation of individual linear integrated circuit
devices is described in this section using waveforms or
graphic techniques to illustrate their circuit action.
GENERAL DESCRIPTION
Introduction
In the following overall functional description of the
instrument, refer to the basic block diagram, Figure 3-1,
and to the detailed block diagrams located in the
“ Diagrams" section of this manual. Each major block in
the diagram represents a major circuit within the instru­
ment. In Figure 3-1, the numbered diamond symbol in each
block indicates the schematic diagram number. Much of
the analog portion of the oscilloscope operates without
direction from the Microprocessor circuitry. These portions
of the instrument are described first, with appropriate
references to areas that either provide information to the
Microprocessor or are controlled by the instrument's
storage circuitry. The Microprocessor and Storage circuit
descriptions follow the more conventional portions of the
instrument’s circuitry.
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 V 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
GND position of the input coupling switch. In the GND
position, the ac-coupling capacitor is allowed to precharge
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. Information about the Input Coupling switch
and the channel VOLTS/DIV switch positions is read by
the Microprocessor. These signals control the STORE
mode ground-reference acquisition and the crt readout
displays of the Input Coupling and VOLTS/DIV switch set­
tings of the active channel(s).
Scaled output signals from the Attenuators are applied
to the Vertical Preamplifiers for amplification. The Chan­
nel 2 Preamplifier has additional circuitry, permitting the
operator to invert the Channel 2 display on the cathode-
ray tube (crt). Trigger pickoffs in each channel supply a
3-1