Theory of Operation
Processing and Display
System
The processing
and display system consists of the display ASIC, DRAM, and
system oscillator. Digitized acquisition s amples are received by the display
ASIC and s tored in DRAM. Once data are received b y the display ASIC, various
corrections are applied, display rasterization is performed, and the waveform is
placed in a display buffer. At the same time, the waveform is read from the display
buffers and written to the LCD. Additional circuitry in the display ASIC supports
scanning th
e front panel, handling DRAM refresh, providing the processor
clock, and performing various memory mapp ing tasks required by all elementary
microprocessor based systems. In a 4-channel system, the two display ASICs are
interconnected so that one ASIC can provide display information for the second.
The processing and display system handl es some of the computational tasks.
Other tasks a re 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. Channel 1 and Channel 2 data may
be combined in all of the supported ways.
Input Signal Interface
BNC connectors are mounted on the Main board for all signal inputs. The signal
input
s are compatible with the supplied TPP0101 and TPP0201 probes.
Probe Compensation
The Probe Comp and ground terminals are provided for probe adjustment.
External Trigger
The Ext Trig channel is processed on the chain containing the highest numbered
nor
mal input channel.
Main Board Power
To support various functions on the Main board, several secondary power supplies
are generated. For the ampliļ¬er and acquisition ASICs, the Main board creates a
+2
.5 V and -2.5 V supply. The +2.5 V supply is derived from the +3.3 V logic
supply. The -2.5 V supply is derived from the -4 V supply. One three-terminal
regulator provides +5 V for internal uses. A second three-terminal regula tor
provides USB power to preclude USB faults from seriously disrupting operation
of the oscilloscope.
An additional power supply provides the LCD bias voltage, which ranges from
+19 to +28 V, depending on contrast setting and display type. This +28 V supply
has a temperature sensor on the Front-Panel board that varies the output voltage of
the supply to maintain contrast over a wide temperature range.
TDS2000C Series Oscilloscope Service Manual 3ā5
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