Tektronix 2445, Инструкция по эксплуатации

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THEORY OF OPERATION
Section 3 —2445 Service
INTRODUCTION
SECTION ORGANIZATION
This section contains a functional description of the
2445 Oscilloscope circuitry. The discussion begins w ith an
overview of the instrument functions and continues w ith
detailed explanations of each major circuit. Reference is
made to supporting schematic and block diagrams which
w ill facilitate understanding o f the text. These diagrams
show interconnections between parts o f the circuitry,
identify circuit components, list specific component values,
and indicate interrelationships w ith front-panel controls.
The detailed block diagram and the schematic diagrams
are located in the tabbed "Diagrams" section at the rear of
this manual, while smaller functional diagrams are con­
tained within this section near the associated text. The
particular schematic diagram associated with each circuit
description is identified in the text, and the diagram
number is shown (enclosed w ithin a diamond symbol)
on the tab of the appropriate foldout page. For optimum
understanding of the circuit being described, refer to both
the applicable schematic diagram and the functional block
diagram.
HYBRID AND INTEGRATED
CIRCUIT DESCRIPTIONS
Digital Logic Conventions
Digital logic circuits perform many functions w ithin this
instrument. The operation of these circuits is represented
by specific logic symbology and terminology. Most logic-
function descriptions contained in this manual use the
positive-logic convention. Positive logic is a system of
notation whereby the more positive of two levels is the
TRUE (or 1) state; the more negative level is the FALSE
(or 0) state. In the logic descriptions, the TRUE state is
referred to as HI, and the FALSE state is referred to as LO.
The specific voltages which constitute a HI or a LO vary
between individual devices. For specific device character­
istics, refer to the manufacturer's data book.
Hybrids
Some of the circuits in this instrument are implemented
in hybrid devices. The hybrids are specialized electronic
devices combining thick-film and semiconductor tech­
nologies. Passive, thick-film components and active, semi­
conductor components are interconnected to form the
circuit on a ceramic carrier. The end result is a relatively
small "building b lock" w ith enhanced performance char­
acteristics, all in one package. Hybrid circuits are shown
on schematics simply as blocks w ith inputs and outputs
identified. Information about hybrid functioning is
contained in the related portion o f the Detailed Circuit
Description.
Linear Devices
The operation o f individual linear integrated circuit
devices is described in this section using waveforms or other
graphic techniques to illustrate their operation.
BLOCK DIAGRAM
The following discussion is provided as an aid in under­
standing overall operation of the 2445 Oscilloscope cir­
cuitry before the individual circuits are discussed in detail.
A simplified block diagram o f the 2445 Oscilloscope,
showing basic interconnections, is shown in Figure 3-1.
The diamond-enclosed numbers in each block refer to the
schematic diagram(s) at the rear of this manual in which
the related circuitry is located.
BLOCK DESCRIPTION
The Low Voltage Power Supply is a high-efficiency,
switching supply w ith active output regulation that trans­
forms the ac source voltage to the various dc voltages
required by the 2445. The High Voltage Power Supply
circuit develops the high accelerating potentials required
by the crt, using voltage m ultiplication techniques, and the
DC Restorer provides interfacing for the low-potential
intensity signals from the Z-Axis A m plifier to the crt
control grid.
3-1