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Overview

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 16K 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 Mercury 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 Mercury-4 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 is organized into two completely independent banks, allowing readout of one bank while the other is filled. Peak readout speeds across the USB interface exceed 15 MB/sec.

The Mercury

Features

• Four independent Digital X-ray Processor (DXP) channels
• 4 MB of high-speed memory allows ample storage for timing applications such as mapping with full spectra or multiple ROI's.
• Peak USB 2.0 transfer rates exceed 15 MB/sec.
• Auxiliary port with 40 customizable digital I/O lines. The standard configuration provides trigger, livetime and 6 ROI outputs per channel.
• Peaking time range: 0.1 to 160 microsec
• Maximum throughput up to 1,000,000 counts/sec/channel.
• Digitization: 14 bits at 50 MHz
• Low noise front end offers excellent resolution, and provides excellent performance in the soft x-ray region (110 - 1500 eV).
• Operates with virtually any x-ray detector. Preamplifier type is computer controlled.
• 16 bit gain DAC and input offset are computer controlled.
• Pileup inspection criteria are computer selectable.
• Accurate ICR and livetime for precise deadtime correction and count rate linearity.
• Multi-channel analysis for each channel allows optimal use of data.
• External GATE and SYNC connections for controlling the mapping modes.

Specifications

Architecture

The Mercury 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 (FiPPI).
The Mercury contains four independent DXP Digital Xray Processor (DXP) channels. Each DXP channel accepts a detector preamplifier signal input and produces a FIFO-buffered output stream of 16-bit pulse-height, i.e. energy, measurements. Each DXP also keeps track of its run statistics, including livetime and the number of input counts detected. See §§Error! Reference source not found.-5.4 below for a thorough description of the DXP.

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_Mercury4.html, last updated January 23, 2012
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