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The DXP’s trapezoidal digital FIR filters offer significantly enhanced throughputs and achieve energy resolutions comparable to analog systems, but at a lower cost per detector. Energy resolution is nearly independent of count rate up to maximum throughput. The full computer interface allows all data taking and calibration operations to be automated, greatly reducing the possibility of human error. Data can be collected either into a full spectrum of up to 8K channels or into up to 32 regions of interest (ROI’s) and passed to the host without stopping data collection. The full spectrum allows peak fitting and/or deconvolution to be done on a detector by detector basis, leading to more accurate intensity extractions, particularly where scatter peaks are changing rapidly with energy. The DXP-XMAP operates easily with a very wide range of common detector/preamplifier systems of either polarity, including pulsed optical reset, transistor reset, and resistive feedback varieties. The DXP-XMAP offers several timing modes, including fast scanning with full MCA readout or multiple ROI’s, as well as list mode readout, where time and energy are stored for each event. The onboard memory manager allows full access to the data even during data collection. To allow deadtimeless operation for fast scanning, the memory can be organized into two completely independent banks, allowing readout of one bank while the other is filled. Peak readout speeds across the PCI interface exceed 100 MB/sec.
|Inputs||Analog||Four preamplifier inputs, jumper-selectable input gain. 0dB (x1): 10 kohm impedance, +/- 5V range. 12dB attenuation (1/4 gain): 1kohm, +/- 20V, jumper selectable. Works with common reset or resistive feedback preamplifiers of either polarity.|
(TTL) Each module
has a single LEMO connector which can be programmed to be used for any
of the following functions:
All digital signals are bussed along the PXI backplane. For Gate and Sync, only one signal per backplane segment must be provided.
|Data I/O||Interface||Compact PCI standard, 33 MHz, 32-bit|
|Data Transfer Rate||Memory readout to host: 109 MB/sec|
|Resolution||State of the art,
|Count Rate||OCR to 1 Mcps max (at ICR
> 2 Mcps)
|Throughput||The output count rate (OCR) approaches theoretical values based on input count rate (ICR) and deadtime td, where td equals 2 times peaking time plus dwell time: OCR = ICR * exp(-ICR* td).|
|Integral Non-linearity||<= 0.1% over full
scale output range.
|Pileup Inspection||Pulse-pair resolution typically better than 100 ns unless limited by signal risetime.|
|Digital Controls||Gain||100x range, controlled by 16-bit DAC. Preamplifier gain range 0.1 to 10 mV/keV at standard settings.|
Up to three adjustable thresholds are used simultaneously to support soft x-ray work while maintaining good pileup rejection.
|Filtering||Peaking times 0.1 - 160 microseconds. Adjustable flat top to eliminate ballistic deficit effects.|
|Pileup||Fast channel filter time, pulse detection threshold, and fast channel pileup inspection test limits may be set independently to achieve best results in every x-ray energy regime.|
|Data collection||MCA limits, bin widths, ROI’s|
||MCA||Single Spectrum Mode:
256-16384 bins (32 bits deep).
Multi-Spectrum Mode: 256-16384 bins (16 bits deep).
|ROI's||Up to 32 ROI regions of interest can be defined.|
|Timing||Multiple spectra or sets of ROI’s can be stored; continuous operation is possible using memory in dual-bank configuration.|
|Statistics||Statistics: All values required for pileup correction are available: livetime, realtime, input events, output events.|
|Diagnostics||ADC and filter output traces, baseline distribution, baseline history|
||Overview||XIA provides xManager, a software package for setting up detector arrays and generating configuration files for use by other control packages. Handel, a comprehensive set of C libraries, simplifies integration of DXP-XMAP control into existing data collection packages.|
|Diagnostics||ADC trace, filter outputs, baseline distribution, baseline history|
|Run Control||Start/stop under host control or according to user provided TTL/CMOS logic signals. Run can be ended according to preset realtime, livetime, input or output events, or number of pixels.|
The DXP-XMAP system, shown below, consists of four Digital Xray Processor (DXP) channels, a Digital Signal Processor (DSP), a System FPGA, SRAM memory and a PCI interface. Each of the four DXP channels accepts a preamplified signal input and produces a 16-bit pipelined output stream of x-ray energies.
The Digital X-ray Processor (DXP)
is a proprietary architecture (see Figure 5.2) designed to rapidly measure
the pulse-heights of voltage steps. Shown below are the three major
DXP operating blocks: the Analog Signal Conditioner (ASC), an analog-to-digital
converter (ADC), and the Filter, Peak Detector, and Pileup Inspector
Single Spectrum and Multiple-Spectrum Data Acquisition
In the Single Spectrum mode a data acquisition run produces a single energy spectrum, ranging from 256 bins to 16384 bins, for each DXP processing channel. On-board memory is configured as a single 32-bit device accessible to both the host and the on-board DSP. Each spectral bin is thus a 32-bit value, allowing for up to 4,294,967,295 events per bin. The external logic (LEMO) input can be configured to halt data acquisition, i.e. implemented as a GATE function. Data acquisition runs can be started and stopped manually, or can be stopped automatically according to a preset real time, live time or number of input or output events.
In the Multi-Spectrum Mapping mode a data acquisition run produces multiple spectra for each DXP processing channel, i.e. one spectrum per pixel. Spectrum memory is configured as two 16-bit devices, each accessible to either the host or the on-board DSP. Continuous operation is achieved by reading one memory device while writing the other memory device, and swapping the devices periodically. Each spectral bin is thus a 16-bit value, allowing for up to 65,535 events per bin. The external logic (LEMO) input can be configured to control the pixel advance function, which creates a new spectrum corresponding to a new pixel. Data acquisition runs can be started and stopped manually, or can be stopped automatically according to a preset number of pixels. Pseudo-normal spectrum mode operation is supported for diagnostic purposes, with the following limitations: Data cannot be read out during a run; The 16-bit bins can easily overflow, depending on the run length and input count rate.
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http://www.xia.com/DXP-XMAP.html, last updated
August 9, 2012