Chapter 8. Circuit Description - OPHIR vega User Manual

Chapter 8.
Circuit Description
The Vega has two circuit boards: the lower board with
analog circuit, digital processor and its support circuit,
and power supplies; and the upper board with LCD and its
driver.
Analog Circuit:
The signal from the detector sensor enters the analog
circuit and passes through EMI protection components to
a differential trans-impedance preamplifier. From there it
is further amplified by a programmable gain voltage
amplifier and passes to an Analog-to-Digital (A/D)
converter. All calibration data for the analog circuit is
stored in a memory chip on the main board. There are no
mechanical adjustable components (trimmers etc.) in the
Vega.
Fast Analog Input:
In addition to the above basic analog circuit, the Vega
contains a second fast analog input. This supports
certain Ophir sensors that read energy pulses at higher
rates than can be supported by the basic analog circuit,
but provides less overall accuracy than the above circuit.
The fast analog input consists of an EMI filtered voltage
input that is passed to a first stage of mild voltage
attenuation. This is then passed to a fast A/D converter.
Calibration data is stored on the same memory chip
mentioned above.
Digital Processor:
The digital processor is built around a Freescale MC68332
32-bit micro controller (MCU) with a 16-bit external bus.
The digital circuit includes an upgradeable FLASH chip
that can be programmed in-situ by Vega support
software. In addition there is a static battery-backed
RAM chip totaling 512Kbytes of RAM. The large amount
of RAM allows storage of large amounts of logged data
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