Tektronix TPS2000 Series, Service Manual

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Theory of Operation
TPS2000 Series Digital Storage Oscilloscopes Service Manual
3--3
lated and sent to the acquisition ASIC. Control of the amplifier ASIC across the
isolation boundary is provided by an optocoupler. Power is provided to each
amplifier ASIC and associated circuits by an isolated switching power supply,
dedicated to each channel
Each acquisition ASIC contains samplers and peak detectors, an amplifier, an
A/D converter, and the trigger logic. The digitized waveform samples are
transferred to the processing and display ASIC. In four-channel systems, the two
acquisition ASICs are interconnected so that a trigger on one ASIC can produce a
trigger on the other.
The processor system adds the microprocessor and FLASH ROM to the
processing and display system. The processor system interprets the front-panel
control changes detected by the display ASIC, provides control parameters based
upon user setting requests, computes waveform measurements, and manages the
internal and external peripherals. Saved setups, waveforms, and calibration
constants are stored in nonvolatile memory (NVRAM). The processor system
shares DRAM with the display system.
The processing and display system consists of the display ASIC, DRAM, and
system oscillator. Digitized acquisition samples are received by the display ASIC
and stored in DRAM. Once data are received by the display ASIC, various
corrections are applied, display rasterization is performed, and the waveform is
placed into a display buffer. At the same time, the waveform is being read from
the display buffers and written to the LCD. Additional circuitry in the display
ASIC supports scanning of the front panel, provides DRAM refresh, processes
the clock, and performs various memory mapping tasks required by all elementa-
ry microprocessor-based systems. In a four-channel system, the two display
ASICs are interconnected so that one ASIC may provide display information for
the second.
The processing and display system handles some of the computational tasks.
Other tasks are performed by the processor system. Since all array processing is
performed in the processing and display system, no computations can be
performed that involve data from two different channel sets. Thus, subtracting
channel 3 data from channel 2 is prohibited.
The PROBE COMP and ground terminals are provided for probe adjustment.
The IO board supplies the Acquisition board with 5.0, 3.0, 3.3, and 15 VDC.
These sources are used directly or as sources for other converters on the
Acquisition board. The Acquisition board supplies 35 volts used for LCD bias
and for series-strings of LEDs on the front panel for button illumination. The
LCD bias varies the contrast, and is temperature compensated by a thermistor
mounted on the front panel.
Processing and Display
System
Probe Compensation
Acquisition Board Power