Tektronix TDS 340A, Technical Reference

Page: 44 / 288

TDS 340A, TDS 360 & TDS 380 Technical Reference
3–1
Theory of Operation
This chapter describes the electrical operation of the TDS 340A, TDS 360, and
TDS 380 at the module level.
Logic Conventions
This manual refers to digital logic 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
non-active state. The specific voltages that constitute a high or low state vary
among the electronic devices.
Active-low signals are indicated by a tilde (~) prefixed to the signal name
(~RESET). Signal names are considered to be either active-high, active-low, or
to have both active-high and active-low states.
Module-Level Overview
This overview describes the basic operation of each circuit module as shown in
Figures 3–1 through 3–2.
A signal enters the oscilloscope through a probe connected to a BNC on the A11
(TDS 340A), A12 (TDS 360), or A13 (TDS 380) Main Board.
Attenuators.
Circuitry in the attenuator selects the input coupling and attenuation
factor. The processor system controls the attenuators with a serial interface.
Probe Coding Interface. The probe coding interface signals pass through the Main
Board to the A6 Front Panel, which senses them.
Acquisition System. The acquisition system amplifies 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 trigger,
acquisition timing, and acquisition mode generation and control circuitry.
Input Signal Path