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RX1200 is a single-channel, 200 MHz digital data acquisition system designed for radiation detection and spectroscopy. RX1200 can be used with almost any type of radiation detector. With 12-bit sampling resolution, RX1200 is well suited for spectroscopy applications with scintillation detectors.

Since the pulse integration is implemented digitally in the FPGA, no preamplifier is required with scintillation detectors. RX1200 can be reprogrammed via high-speed USB port in a small fraction of second. This feature along with 24-pin user interface (0.1”) and eight LED’s on board, makes the RX1200 a perfect solution for developing customized firmware for digital radiation measurement and
spectroscopy.

RayCode is an FPGA firmware (200 MHz) developed for RX1200 to capture and digitally processes signal pulses from scintillation detectors. It includes a scope module to capture radiation pulses (digitizer) and a Multi-Channel Analyzer (MCA) module to reconstruct the energy spectrum. The MCA is implemented in a 4K, 32-bit memory configuration. The on-board PROM is shipped with RayCode.

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Unlike traditional analog spectroscopy systems in which only one sample from shaped pulses is taken by a peak-sensitive Analog-to-Digital Converter (ADC), in a digital spectrometer, the whole signal pulse is captured by a fast ADC to determine the corresponding energy deposition in detector. This brings significant improvements to the world of radiation spectroscopy, among them: pulse processing is easy to edit, no bulky electronics, post-processing is possible, more cost effective, effects like pile-up can be rejected in the processing level, and much less power requirement.

In RX1200, signal pulses from the radiation detector are sampled every 5 nanoseconds (sampling rate of 200 MHz). As depicted in the functional block diagram, the input signal from the detector (a) is passed through an analog conditioning stage before it is digitally captured by the ADC. At this stage, the detector signal level is adjusted by three signals (b, c and d) from an on-board Digital-to-Analog Converter (DAC). These signals, which are digitally adjustable from the PC side, determine three parameters: amplification gain, input offset and ADC offset.

The same DAC provides another analog signal (e) which can be used to control an external high-voltage unit. These four analog signals can be adjusted in 4096 steps (12 bits). At the end of this stage, a third-order low-pass Bessel filter (anti-aliasing filter) with a cutoff frequency of 90 MHz is used to remove high-frequency components from the input signal.

Filtered analog signal (f) is digitally captured by a fast ADC (200 MHz, 12 bits). Digital samples (h) from the ADC are then fed into a Field-Programmable Gate Array (FPGA) for further digital pulse processing. The input clock of ADC (g) is provided by the FPGA. The FPGA synthesizes this clock from a reference clock (USB_CLK, 48 MHz) which is originally generated in the USB processor (m). The ADC itself generates a clock output (i) which is synchronized with its data output (h). To minimize the clock skew and to relax the setup-time constraints, the FPGA uses this clock for all ADC’s data related registers.

a) Analog signal input
b) Gain adjustment signal
c) Input offset adjustment signal
d) ADC offset adjustment signal
e) DAC output (0V to +3.3V)
f) Filtered analog signal
g) ADC clock input (LVDS)
h) ADC data output (LVDS)
i) ADC clock output (LVDS)

Functional Block Diagram of RX1200

j) FPGA configuration port
k) Configuration bit stream from PROM
l) Configuration bit stream from USB port
m) USB clock output
n) USB cable
o) FPGA/USB data bus
p) DAC data
SW1: Configuration mode switch

200 MHz sampling rate
12 bits resolution
USB 2.0 (High Speed)
Programming PROM
FPGA: Xilinx SPARTAN-3, XC3S1000-5FTG256C
FPGA programming via USB, PROM or JTAG
Digitally adjustable Amplfication Gain (-14 to 46 dB, 4096 steps)
Digitally adjustable Input Offset (-330 to +330 mv, 4096 steps)
Digitally adjustable ADC Offset (ADC input range, 4096 steps)
DAC Output (0 to 3.3 v, 4096 steps)
100 mil, 24-pin User Interface Header
8 on-board LEDs, 2 on-panel LEDs (RX1200-D)
Full RayPanel support
Complete API in C++, Visual Basic and MATLAB
On-board PROM shipped with RayCode FPGA firmware

RX1200, 200 MHz Digital MCA/Digitizer
Avicenna
Instruments
Digital Systems for Radiation Detection
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