Tektronix TPS2000 Series, Руководство по обслуживанию

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Theory of Operation
3--2
TPS2000 Series Digital Storage Oscilloscopes Service Manual
Acquisition Board
The Acquisition board of the TPS2000 Series four-channel oscilloscope is
essentially a dual, two-channel oscilloscope tied together through a common
microprocessor, and some special interconnects. This allows the combining of
the display and trigger systems. For this reason, the focus of the Acquisition
board discussion will be on the two-channel system, with differences noted as
necessary.
At a minimum, the Acquisition board contains the following components:
H
Attenuators
H
ASIC amplifier
H
Isolation circuit
H
Digitizer--trigger system ASIC
H
Signal-processing/display/system services ASIC
H
RAM
H
FLASH ROM
H
Microprocessor
H
Internal peripheral interface
H
Power supplies
For a four-channel oscilloscope, the attenuators and ASICs are duplicated. Most
of the other aspects of the circuitry remain unchanged.
Signals from the CH 1, CH 2, and other input connectors pass through attenua-
tors and an AC-coupling switch to the amplifier ASIC. The EXT TRIG input
uses an abbreviated version of this path, without some of the attenuator settings
and the AC coupling switch.
The amplifier ASIC contains buffers and variable gain amplifiers, as well as
filters that provide 20 MHz bandwidth limiting. The task of the amplifier ASIC is
to convert from a 1 M
Ω
single-ended environment in the input to a much lower
impedance differential (and thus less noise-sensitive) environment for the
isolation and acquisition process. The amplifier ASIC assures that the input
signal is amplified to approximately the correct level to allow the fullest possible
use of the isolation circuit and digitizer.
The isolation circuit uses a modulation clock to transfer the input signal across
the isolation boundary via an isolation transformer. The input signal is demodu-
Acquisition System