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XIA LLC Pixie-4 Express User Manual

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Pixie-4 Express
User Manual
Version 4.47
February 15, 2018
Hardware Revision: B
Software Revision: 4.47
XIA LLC
31057 Genstar Rd
Hayward, CA 94544 USA
Email: support@xia.com
Tel: (510) 401-5760; Fax: (510) 401-5761
http://www.xia.com/
Information furnished by XIA LLC is believed to be accurate and reliable. However, no responsibility is assumed by
XIA for its use, or for any infringements of patents or other rights of third parties which may result from its use. No
license is granted by implication or otherwise under any patent or patent rights of XIA. XIA reserves the right to
change hardware or software specifications at any time without notice.

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Summary of Contents for XIA LLC Pixie-4 Express

  • Page 1 Information furnished by XIA LLC is believed to be accurate and reliable. However, no responsibility is assumed by XIA for its use, or for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of XIA.

  • Page 2: Table Of Contents

    Voltage Ratings ............................. 5 Servicing and Cleaning ......................... 5 Warranty Statement ............................6 Contact Information: ..........................6 Manual Conventions ............................. 7 Introduction ............................8 Pixie-4 Express Features ....................... 9 Specifications ..........................10 System Requirements ........................11 1.3.1 PXIe Chassis ........................11 1.3.2 Host Computer ........................
  • Page 3 6.7.2 Count time and dead time counters ..................59 6.7.3 Count Rates ......................... 61 6.7.4 Dead time correction in the Pixie-4 Express ............... 62 Synchronized Data Acquisition ......................63 Clock Distribution ........................63 Trigger Distribution ........................63 7.2.1 Trigger Distribution Within a Module ................63 7.2.2...
  • Page 4 Pixie-4 Express User Manual Version 4.31 7.6.2 Coincidences Between Modules ..................72 Using Pixie-4 Express Modules with Clover detectors ..............73 Appendices ..............................74 Appendix A: Hardware information ....................... 74 Front end switches for termination and attenuation ................74 Front Panel LEDs ..........................75 PXI backplane pin functions .......................

  • Page 5: Safety

    Pixie-4 Express User Manual Version 4.31 Safety Please take a moment to review these safety precautions. They are provided both for your protection and to prevent damage to the Pixie module and connected equipment. This safety information applies to all operators and service personnel.

  • Page 6: Warranty Statement

    In order to obtain service under this warranty, Customer must notify XIA LLC of the defect before the expiration of the warranty period and make suitable arrangements for the performance of the service.

  • Page 7: Manual Conventions

    Pixie-4 Express User Manual Version 4.31 Manual Conventions The following conventions are used throughout this manual Convention Description Example » The » symbol leads you The sequence through nested menu items File»Page Setup»Options directs you to pull and dialog box options.

  • Page 8: Introduction

    Pulse heights are calculated to 16-bit precision and can be binned into spectra with up to 32Ki channels. The Pixie-4 Express supports coincidence spectroscopy and can recognize complex hit patterns.

  • Page 9: Pixie-4 Express Features

    Pixie-4 Express User Manual Version 4.31 1.1 Pixie-4 Express Features  Designed for high precision γ-ray spectroscopy with HPGe detectors, timing with fast scintillators (NaI, LaBr3, etc), pulse shape analysis to extract time, position, and/or particle type in segmented or strip detectors, phoswich detectors, or neutron detectors coincidence acquisition ...

  • Page 10: Specifications

    Pixie-4 Express User Manual Version 4.31 1.2 Specifications Front Panel I/O 4 analog inputs. Signal Input (4x) Switch selectable input impedance: 50Ω and 2kΩ. Switch selectable input attenuation 1:8 and 1:1 for either impedance. Input range: After termination and attenuation, up to ±2.5V DC can be added to compensate signal DC offsets.

  • Page 11: System Requirements

    Pixie-4 modules in a PXIe chassis, and a gamma ray detector with appropriate power supplies. 1.3.1 PXIe Chassis The Pixie-4 Express can be operated in a peripheral PXIe or PXIe/PXI hybrid slot of any standard 3U PXIe chassis. 1.3.2 Host Computer The Pixie module communicates with a host computer through a PCI Express (PCIe) interface.

  • Page 12: Detector Signals

    Numbers in brackets show the minimum currents supplied by the chassis per PXIe standard 1.3.6 Connectors and Cabling The Pixie-4 Express uses SMA connectors for the analog inputs from the detectors. SMA to BNC adapter cables are provided with the module.

  • Page 13: Installation

    Pixie-4 Express modules in the chassis, it will detect new hardware and try to find drivers for it. (A Pixie-4 Express module will be detected as a new device every time it is installed in a new slot.) While there is no required order of installation of the driver software, the...
  • Page 14 Feel free, however, to add folders and subfolders at your convenience. Windows will detect new hardware (the Pixie-4 Express modules) and should find the drivers automatically. If not, direct it to the “drivers” directory in the Pixie-4 Express software distribution installed in step 6.

  • Page 15: Getting Started

    Pixie-4 Express User Manual Version 4.31 2.3 Getting Started To start the Pixie Viewer, double-click on the file “Pixie.pxp” in the installation folder. The Pixie Viewer offers the following online help options and short cuts:  All panels have a [Help] button that opens a help window with description of the panel's controls.
  • Page 16 Pixie-4 Express User Manual Version 4.31 possible solutions. If you want to try the software without a chassis or modules attached, click on [Offline Analysis]. After the system is initialized successfully, you will see the Main control panel that serves as a shortcut to the most common actions and from which all other panels are called.
  • Page 17 Pixie-4 Express User Manual Version 4.31 version, if the signal looks unusually noisy, click on the [Calibrate] button to automatically match gain and offset of the 2 ADC cores. Figure 2-4: O panel SCILLOSCOPE In the Energy tab of the P...
  • Page 18 Pixie-4 Express User Manual Version 4.31 At this stage, you may not be able to get a spectrum with good energy resolutions. You may need to adjust some settings such as energy filter rise time and flat top as described in section 3.5.

  • Page 19: Navigating The Pixie Viewer

    Pixie-4 Express User Manual Version 4.31 3 Navigating the Pixie Viewer 3.1 Overview The Pixie Viewer consists of a number of graphs and control panels, linked together by the control panel. The Pixie Viewer comes up in exactly the same state as it was when last saved to file using File->Save Experiment.

  • Page 20: Setup Group

    Pixie-4 Express User Manual Version 4.31 3.2 Setup Group In the setup group, there is a button to open the S panel, which is used to boot the TART modules. The Open Panels popup menu leads to one of the following panels: P...
  • Page 21 Pixie-4 Express User Manual Version 4.31 computed from acquired waveforms using the current settings. The threshold value is scaled with the trigger filter rise time, therefore it is not limited to integer numbers. 3.2.1.2 Energy Tab The Energy tab contains the settings for the energy filter and the subsequent computation.
  • Page 22 ADC calibration. The ADC used on 500 MHz versions of the Pixie-4 Express actually consists of two ADC cores on a single IC, which need to be calibrated for matched gain, offset and phase. Normally, these calibration settings are read from the module's non-volatile memory at boot time, but sometimes, for example at temperature changes, it may be required to recalibrate the cores.

  • Page 23: Oscilloscope

    Offset (V), which directly sets the offset voltage. The traces from different channels are not acquired synchronously but one after the other. Therefore even if coincident signals are connected to the Pixie-4 Express inputs, the Oscilloscope will show unrelated pulses for each channel.

  • Page 24: Chassis Setup

    HASSIS ETUP Examples are trigger distribution between modules, coincidence settings between modules, and the operation of the Pixie-4 Express’s front panel input. See sections 7.2.2 and 7.6.2 for details. 3.3 Run Control Group The Run Control group in the M control panel has the most essential controls to start and stop runs, and to define or monitor the run time and the number of spills.

  • Page 25: Mca Spectrum

    Pixie-4 Express User Manual Version 4.31 the output count rates of the four channels in run types 0x400 and 401, but the rate of 4- channel events in Run Type 0x402. . The popup menu Open Panels leads to panels to view the output data from the data acquisition in detail.

  • Page 26: Run Statistics

    3.4.3 R TATISTICS The R panel shows the counting times and count rates measured by the TATISTICS Pixie-4 Express. The numbers can be updated by clicking the [Update] button and read © 2017 XIA LLC...

  • Page 27: File Series

    See section 3.6 for a more detailed description 3.5 Optimizing Parameters Optimization of the Pixie-4 Express’s run parameters for best resolution depends on the individual systems and usually requires some degree of experimentation. The Pixie Viewer includes several diagnostic tools and settings options to assist the user, as described below.

  • Page 28: Threshold And Trigger Filter Parameters

    Pixie-4 Express User Manual Version 4.31 take a run of 60s or so for each and note changes in energy resolution. Then fine tune the rise time. The flat top usually needs only small adjustments. For a typical coaxial Ge-detector we suggest to use a flat top of 1.2µs.

  • Page 29: File Series

    The 500 MHz ADC used on some variants of the Pixie-4 Express is actually a combination of two 250 MHz ADC cores on a single IC. For best performance, the two cores have to be calibrated to match in gain, offset and phase.

  • Page 30: File Series To Scan Filter Parameters

    Pixie-4 Express User Manual Version 4.31 of the P panel, there is a checkbox named New files every, followed by ARAMETER ETUP a control field to enter an interval N. If checked, every N spills during the run the data file is closed, spectra, settings and statistics are saved, and future data is saved to a new file with incremented run number.

  • Page 31: File Series Analysis

    Pixie-4 Express User Manual Version 4.31 in the D panel to the values required for the scan, and set the run ECORD PTIONS time to the total time required (interval N in the D panel times the ECORD PTIONS number of settings).

  • Page 32: Data Acquisition And Data Structures

    The list mode data is continuously transferred from the Pixie module to the host PC. There are currently three types of list mode runs implemented in the Pixie-4 Express: General purpose (0x400), text only (0x401), and group mode (0x402): ...
  • Page 33 “spills” have been collected, as determined by the Pixie Viewer. A spill here means 2 MB of data read from the SDRAM FIFO. Unlike the Pixie-4, the Pixie-4 Express never stops the acquisition for data readout. List mode data is buffered in the SDRAM FIFO, and moved to the host PC on one end while being written by the firmware on the other end.

  • Page 34: Summary Of Run Types

    Pixie-4 Express User Manual Version 4.31 4.1.2.2 Compressed Data Formats The output data of list mode runs can be reduced by using one of the compressed formats described below. The key differences are that as less data is recorded for each event, there is room for more events in the SDRAM FIFO, less time is spent per event to read out data to the host computer, and data files are smaller.

  • Page 35: Output Data Structures

    16Ki sum energy MCA. The memory can be read out via the PCIe data bus at any time, though not at the full burst rate. The total MCA memory size on the Pixie-4 Express is 512Ki words. It can be reorganized for special applications (e.g., 2D spectra or channel sum spectra).
  • Page 36 Pixie-4 Express User Manual Version 4.31 4.2.2.2 Event Data in Run Type 0x400 Following the file header, in Run Type 0x400 the single channel event records are stored in sequential order. Each event starts out with a channel header of length ChanHeadLen.
  • Page 37 Pixie-4 Express User Manual Version 4.31 EvtInfo Coincidence test result Logic level of backplane VETO line If set, indicates event is piled up If set, indicates waveform FIFO full If set, indicates this channel was hit (else the event was recorded based on...
  • Page 38 Pixie-4 Express User Manual Version 4.31 4.2.2.4 Event Data in Run Type 0x402 In Run Type 0x402, following the file header, the 4-channel event records are stored in sequential order. Each event starts out with an event header of length ChanHeadLen.
  • Page 39 Pixie-4 Express User Manual Version 4.31 The hit pattern and event status flags are the same as in Table 4-4 above, except that the flags refer to “at least one channel”, essentially an OR of the 4-channel flags (table 4.7).
  • Page 40 Pixie-4 Express User Manual Version 4.31 4.2.2.5 File Footer in Run Type 0x400 and 0x402 At the end of the file, an “end of run” (EOR) record is appended. This is created by the DSP so that the software can recognize the end of the data stream to be saved. Its content is shown in Table 4.5.
  • Page 41 Pixie-4 Express User Manual Version 4.31 4.2.2.6 Special List Mode Records In some variants of the firmware, there can also be special records with additional information. These are listed in the tables below: Word # Variable Description EvtPattern RSR pattern (low): 0x0004...

  • Page 42: List Mode Data Values

    4.2.3.1 List Mode Time Stamps In the Pixie-4 Express, there is a 56-bit time counter. It is incremented at a rate of 125 MHz by 4 ticks, so that the unit of the LSB is 2ns. Hence, the 56-bit word can span a time interval of over 800 days before rolling over.
  • Page 43 Pixie-4 Express User Manual Version 4.31 4.2.3.3 List Mode PSA Values PSA values are described in a separate manual specific to the PSA functions implemented for a specific variant. © 2017 XIA LLC...

  • Page 44: Hardware Description

    This section concentrates on the functionality aspect. Technical specification can be found in section 1.2. Figure 5.1 shows the functional block diagram of the Pixie-4 Express. Figure 5-1: Functional block diagram of the Pixie-4 Express front-end data acquisition and signal processing card. 5.1 Analog Signal Conditioning Each analog input has its own signal conditioning unit.

  • Page 45: Pulse Processing

    Therefore, the FPGA on the Pixie-4 Express processes the data stream at 125 MHz. For 250 MSPS (or 500) MSPS variants each channel's 16 (or 14) bit data stream is “de- serialized”...

  • Page 46: Pci Express Interface

    DSP; the DSP only enables a direct FPGA-internal transfer from the channel processing block to the SDRAM interface block, at a rate of 1GByte/s. The DSP also controls the overall operation of the Pixie-4 Express. The host computer communicates with the DSP via the PCIe interface. Reading and writing data to DSP memory does only temporarily pause its operation, and can occur even while a measurement is underway.

  • Page 47: Theory Of Operation

    Pixie-4 Express User Manual Version 4.31 6 Theory of Operation 6.1 Digital Filters for -ray Detectors Energy dispersive detectors, which include such solid state detectors as Si(Li), HPGe, , CdTe and CZT detectors, are generally operated with charge sensitive preamplifiers as shown in Figure 6.1 (a).
  • Page 48 Pixie-4 Express User Manual Version 4.31 it from the value of the average over the points after the step. That is, as shown in Figure 6-2, averages are computed over the two regions marked “Length” (the “Gap” region is omitted because the signal is changing rapidly here), and their difference taken as a measure of V .

  • Page 49: Trapezoidal Filtering In A Pixie Module

    Pixie-4 Express User Manual Version 4.31 The Pixie-4 Express takes a different approach because it was optimized for high speed operation. It implements a fixed length filter with all W values equal to unity and in fact computes this sum afresh for each new signal value k. Thus the equation implemented is: ...

  • Page 50: Baselines And Preamplifier Decay Times

    Pixie-4 Express User Manual Version 4.31 ADC output Filter Output 33x10 2L+G 10.0 10.5 11.0 11.5 12.0 12.5µs Time Figure 6-3: Trapezoidal filtering of a preamplif 6.3 Baselines and Preamplifier Decay Times Figure 6.4 shows an event over a longer time interval and how the filter treats the preamplifier noise in regions when no -ray pulses are present.

  • Page 51: Thresholds And Pile-Up Inspection

    All that is required is to take the filter sums, reconstruct the energy V , and add it to the spectrum. In the Pixie-4 Express, the filter sums are continuously updated in the FPGA (see section 5.2), and are captured into event buffers.
  • Page 52 Pixie-4 Express User Manual Version 4.31 The slow filter value captured following PEAKSAMP is then the slow digital filter’s estimate of V . Using a delay line allows to stage sampling of multiple pulses even within a PEAKSAMP interval (though the filter values themselves are then not correct representations of a single pulse’s height).

  • Page 53: Filter Range

    Pixie-4 Express User Manual Version 4.31 intervals. The fast filter has a filter length L = 0.1s and a gap G =0.1s. The slow filter has L = 1.2s and G = 0.35s. Because the trapezoidal filter is a linear filter, its output for a series of pulses is the linear sum of its outputs for the individual members in the series.

  • Page 54: Data Capture Process

    Version 4.31 6.6 Data Capture Process The data capture in the Pixie-4 Express is based on the principle that for every detected rising edge, one record is assembled from the continuously running processes for waveform capture and energy filters. As some of the processes are not finished by the time of the rising edge, input data or capture signals are delayed appropriately.
  • Page 55 Pixie-4 Express User Manual Version 4.31 6.7.1.1 Dead time associated with each pulse 1. Filter dead time At the most fundamental level, the energy filter implemented in the FPGA requires a certain amount of pulse waveform (the “filter time”) to measure the energy. Once a rising...
  • Page 56 In the Pixie-4 and Pixie-500, there was additional dead times associated with reading out the data, since only one event at a time was stored in the FPGA. In the Pixie-4 Express, up to 500 events (and/or total 8Ki waveform samples) are buffered in the FPGA. Thus new events are accepted while captured ones are read out and processed further, and these types of dead time are eliminated.
  • Page 57 6.7.1.2 Dead time associated with external conditions There are three dead time effects that originate from outside the trigger/filter FPGA. The first two have the effect of stopping the Pixie-4 Express count time counter, the last is counted separately. Figure 6-9: The count time counter is stopped when the signal is out of range and when events are rejected because of a processing backlog (e.g.
  • Page 58 6.7.1.3 Dead time associated with host readout The final type of dead time comes from the readout of data from Pixie-4 Express memory to the host PC. In MCA mode, this is limited to the access arbitration for the spectrum memory.

  • Page 59: Count Time And Dead Time Counters

    ADC data in real time, for example to 4 x 2 bytes x 500 MSPS = 4 GB/s, is still beyond the capacity of the PCIe x4 interface used by the Pixie-4 Express. Few, if any, PXIe crates, controllers, and/or hard drives can accommodate such rates. Streaming ADC data is therefore only possible if some kind of data compression is applied, please contact XIA for details.
  • Page 60 Pixie-4 Express User Manual Version 4.31 DSP finished all setup routines at the beginning of a run, omits the times the ADC signal is out of range, each channel's local 500-event buffer is full, or the SDRAM memory is full and ends when the DSP encounters an end run condition (e.g.

  • Page 61: Count Rates

    GATE PULSEs, which are counted in the variable GCOUNT. 6.7.3 Count Rates Besides the count time and dead times, the Pixie-4 Express counts the numbers of triggers in each channel, FASTPEAKS, the number of valid single channel events, NUMEVENTS, and the number of valid pulses stored for each channel, NOUT.

  • Page 62: Dead Time Correction In The Pixie-4 Express

    ICR as a function of measured OCR, real time and dead time. In the Pixie-4 Express, the input count rate is measured directly with the trigger filter, and so the system dead time bears only theoretical or diagnostic value. For any measurements where accurate determination of true (source) counts are required (activity measurements), the empirical ratio ICR/OCR is the only really unbiased quantity for dead time correction.

  • Page 63: Synchronized Data Acquisition

    PXIe backplane. 7.1 Clock Distribution Unlike the Pixie-4, the Pixie-4 Express uses the 10 MHz and 100 MHz clocks provided by the PXI Express chassis. These clocks are routed on the backplane to tight tolerances and ensure that all modules receive the same clock with very little phase skew. Every module in the chassis is therefore a clock slave to the backplane, and no jumpers or switches are required to change the clock mode.

  • Page 64: Trigger Distribution Between Modules

    (wired-OR). Starting in release 4.2A, the Pixie-4 Express front panel input can be routed to this backplane line or used as an external trigger within a single module only. The setup is as...

  • Page 65: Run Synchronization

    7.3 Run Synchronization It is possible to make all Pixie-4 Express modules in a system start and stop runs at the same time by using a wired-OR SYNC line on the PXIe backplane. The feature is enabled by checking the corresponding checkbox in the Run Control tab of the Pixie Viewer.

  • Page 66: External Gate And Veto

    In the Pixie-4 gate logic, the approach was to reject and count while Gate/Veto is high and invert the incoming signal to be high at the right time. In the Pixie-4 Express, the approach is reversed: there are now options to reject and count while high or low, and the Veto signal is used directly (the Gate signal can still be delayed and re-pulsed).

  • Page 67: Shaping Of External Signals

    The Veto signal is used without any modification as fed into the front panel MMCX connector of the Pixie-4 Express. The Veto signal is distributed on the PXI backplane as an inverted wired OR – 3.3V (logic high) on the MMCX connector drives the backplane low, 0V (logic low) releases the backplane to be pulled up by a resistor.

  • Page 68: Marking Events

    Pixie-4 Express User Manual Version 4.31 Delay Window Window Input: Counting: Shaping: - Front Panel 10pin - Add Delay - At Rising Edge - Use Veto from - Add Delay and Make Pulse on Rising Edge and while High MMCX or backplane...

  • Page 69: Counting Veto/Gate Pulses And Times

    “accept” pulse with appropriate delay for the pileup inspection if more than 2 channels fire at the same time; logic high for accept. That “accept” pulse is connected to the Veto input. Pixie-4 Express settings are set to count at the rising edge and reject when low.

  • Page 70: External Status

    Pixie-4 Express User Manual Version 4.31 7.5 External Status An external “Status” signal can be distributed to all modules on the PXI backplane. The status of that line is also latched at the time of trigger and included in the event status flags of the list mode data.
  • Page 71 Pixie-4 Express User Manual Version 4.31 the middle of its coincidence window. This data become part of the event status flags, and the DSP can decide to accept or reject events based on this information. The plot below shows the time of arrival difference histogram for an acquisition using one periodic and one quasi-random pulser with a Coincidence Window of 800 ns.

  • Page 72: Coincidences Between Modules

    Pixie-4 Express User Manual Version 4.31 recognized separately. Event info bit 4 identifies such “group trigger without local hit” records, also their energy is set to zero unless the “estimate energy” option is set. In Run Type 0x402, both the local time and the event time are recorded ...

  • Page 73: Using Pixie-4 Express Modules With Clover Detectors

    8 Using Pixie-4 Express Modules with Clover detectors When working with clover detectors, the Pixie-4 Express can be operated in a specific “clover mode”. In this mode, the DSP will calculate the pulse height for each channel as in normal operation, and in addition – for events with hits in more than one channel – calculate the sum of individual channel energies.

  • Page 74: Appendices

    (termination) and dashed blue (attenuation) arrows. On the PCB, inverse labels describe the switch positions. Figure 8-1: Simplified input stage of Pixie-4 Express showing switches, input termination and attenuation, and the overvoltage protection circuit. © 2017 XIA LLC...

  • Page 75: Front Panel Leds

    Pixie-4 Express User Manual Version 4.31 Front Panel LEDs The Pixie-4 Express has 3 LEDs on the front panel.  A green LED indicates the firmware has been booted correctly and clocks have been programmed.  A yellow LED indicates that a run is in progress. This can be a very short flash, e.g.

  • Page 76: Pxi Backplane Pin Functions

    GATE input channel 1 LBR3* Right neighbor reserved Table 8-2: Pins of the J2 or XJ4 backplane connector defined in the PXI(e) standard used by the Pixie-4 Express. A * indicates the pin is not available in PXIe standard © 2017 XIA LLC...

  • Page 77: High Density Front Panel Digital Connector

    Pixie-4 Express User Manual Version 4.31 High Density Front Panel Digital Connector Hit 3 (out) Hit 2 (out) Hit 1 (out) Hit 0 (out) Timer Clear (out) Gate 3 (in) Gate 2 (in) Gate 1 (in) Gate 0 (in) Gobal trigger (out) Table 8-3: Pinout of the h10-pin high density front panel connector as seen from the front of the module.

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