Tektronix DSA8200 Series, Service Manual

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DSA8200 Digital Serial Analyzer and Modules Service Manual
2- 1
Theory of Operation
This chapter describes the electrical operation of the instrument and sampling
modules. The diagrams in Chapter 9 show the interconnections of the major
circuit blocks.
Logic Conventions
The instrument contains many digital logic circuits. This manual refers to these
circuits with standard logic symbols and terms. Unless otherwise stated, all logic
functions are described using the positive-logic convention: the more positive of
the two logic levels is the high (1) state, and the more negative level is the low
(0) state. Signal states may also be described as “true”, meaning their active
state, or “false”, meaning their nonactive state. The specific voltages that
constitute a high or low state vary among the electronic devices.
Mainframe Overview
This mainframe overview describes the basic operation of each functional circuit
block as shown in Figure 5--1 on page 5--2.
The instrument control system is a dual Wintel/PowerPC based processor board.
The platform features VGA resolution flat-panel display, transparent touch
screen and user front-panel with direct access to commonly used scope functions.
The instrument is also equipped with a mouse pointing device to facilitate access
to more advanced scope functions.
A signal enters the instrument through a direct coaxial connection to the input
connector on a sampling module, or a real time probe connected to the sampling
module channel.
Acquisition System.
The acquisition system conditions the input signals, samples
them, converts them to digital signals, and controls the acquisition process under
direction of the processor system. The acquisition system includes the multi-
source trigger, acquisition timebase, and acquisition mode generation and control
circuitry. The acquisition board is located in the bottom compartment of the
instrument and can accommodate four small slot sampling plug-ins, two large
slot plug-ins and a trigger/holdoff subsystem. Up to 8 vertical channels are
accommodated simultaneously. Channels 1, 2, 3, and 4 can be either large or
small slots. The presence of a module in one or both large slots displaces the
small slot functionality in the corresponding small slots. The external trigger and
General
Input Signal Path