Tektronix TDS1001C-EDU, Service Manual

Page: 36 / 114

Theory of Operation
Main Board
The Main board is also called the acquisition board. The Main board of the
4-channel oscilloscopes is essentially two 2-channel oscilloscopes tied together
through a common microprocessor, and some special interconnects to support
combining the display and trigger systems. The focus of the Main board
discussion is the 2-channel system, with differences for the 4-channel models
noted as necessary.
At a minimum, the Main board contains attenuators, an ampli fi er ASIC, a
digitizer/trigger system ASIC, a signal processing/display/system services FPGA,
RAM,
fl ash PROM, a system microprocessor, USB controller, USB RAM, system
communication RAM, and special power supplies. For a 4-channel oscilloscope,
the attenuators are duplicated. Most of the other aspects of the circuitry remain
unchanged.
Acquisition System Signals from the channel 1 and channel 2 and other input connectors pass through
attenuators and an AC-coupling switch to the ampli fi er ASIC. The Ext Trig input
has an abbreviated version of this path, lacking some of the attenuator settings
and the AC coupling switch.
The ampli fi er ASIC contains buffers and variable gain ampli fi ers, as well as
fi lters that provide 20 MHz bandwidth limiting. The task of the ampli fi er ASIC
is to convert from a 1 M Ω single-ended environment in the front end to a much
lower impedance differential (and thus less noise-sensitive) environment for the
acquisition process. The ampli
fi er ASIC assures that the input signal is ampli fi ed
to a level that will allow the fullest possible use of the digitizer.
The acquisition ASIC contains samplers and peak detectors for each input
channel, a common ampli
fi er, an A/D converter, and the trigger logic. The
digitized waveform samples are transferred to the processing and display FPGA.
In 4-channel systems, the two acquisition ASICs are interconnected so that a
trigger on one ASIC can cause a trigger on the other.
The processor system adds the microprocessor and fl ash PROM to the processing
and display system. The processor system interprets the front-panel control
changes detected by the display ASIC, provides control parameters based on
user setting requests, computes waveform measurements, and manages the USB
interfaces via the dedicated USB controller. Saved setups, waveforms, and
calibration constants are stored in nonvolatile memory sections within the
fl ash
PROM. The processor system shares DRAM with the display system.
24 TDS2000C and TDS1000C-EDU Series Oscilloscope Service Manual