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XIA Pixie-4 User Manual

Digital gamma finder (dgf)
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User's Manual
Digital Gamma Finder (DGF)
Pixie-4
Version 2.69, November 2015
XIA LLC
31057 Genstar Road
Hayward, CA 94544 USA
Phone: (510) 401-5760; Fax: (510) 401-5761
http://www.xia.com
Disclaimer
Information furnished by XIA is believed to be accurate and reliable. However, XIA assumes
no responsibility for its use, or for any infringement of patents, or other rights of third parties,
which may result from its use. No license is granted by implication or otherwise under the
patent rights of XIA. XIA reserves the right to change the DGF product, its documentation,
and the supporting software without prior notice.

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Summary of Contents for XIA Pixie-4

  • Page 1 No license is granted by implication or otherwise under the patent rights of XIA. XIA reserves the right to change the DGF product, its documentation, and the supporting software without prior notice.

  • Page 2: Table Of Contents

    7.4 External Gate and Veto (GFLT) ....................61 7.5 External Status ........................... 63 7.6 Coincident Events ........................64 8 Using Pixie-4 Modules with Clover detectors ................... 68 9 Troubleshooting ..........................69 9.1 Startup Problems ........................69 9.2 Acquisition Problems ......................... 71 10 Appendix A ............................

  • Page 3: Overview

    HPGe gamma-ray detectors, but has since been applied to an ever broadening range of applications. The DGF Pixie-4 is a 4-channel all-digital waveform acquisition and spectrometer card based on the CompactPCI/PXI standard for fast data readout to the host. It combines spectroscopy with waveform capture and on-line pulse shape analysis.

  • Page 4: Specifications

    Real time, live time, filter and gate dead time, input and throughput counts. Event data Pulse height (energy), timestamps, pulse shape analysis results, waveform data and ancillary data like hit patterns. PIXIE-4 User’s Manual V2.69 © XIA 2015. All rights reserved.

  • Page 5: Setting Up

    When the host computer is powered up the first time after installing the controller and Pixie-4 modules in the chassis, it will detect new hardware and try to find drivers for it. (A Pixie-4 module will be detected as a new device every time it is installed in a new slot.) While there...

  • Page 6: Getting Started

    9054 Boards” without the “PLX” 2.1.3 Pixie User Interface The Pixie Viewer, XIA’s graphical user interface to set up and run the Pixie-4 modules, is based on WaveMetrics’ IGOR Pro. To run the Pixie Viewer, you have to have IGOR Version 5.0 or higher installed on your computer.
  • Page 7 4 modules have been initialized successfully. Otherwise, refer to the troubleshooting section for possible solutions. If you want to try the software without a chassis or modules attached, click on Offline Analysis. Figure 2.1: The Pixie-4 S panel (above) and M Panel (right)
  • Page 8 Adjust Offsets to automatically set the DC offset. If the pulse amplitude is too large to fall in the display range, decrease the Gain. If the pulses are negative, toggle the Invert checkbox. PIXIE-4 User’s Manual V2.69 viii ©...
  • Page 9 Min and Max fields in the table or by specifying a Range around the tallest peak or the peak with the highest energy. To scale the spectrum in keV, enter the appropriate ratio in the field keV/bin. PIXIE-4 User’s Manual V2.69 © XIA...

  • Page 10: Navigating The Pixie Viewer

    Setup, Run Control, and Results. In the Setup and Results groups, popup menus lead to the panels and graphs indicated in Figure 3.1. PIXIE-4 User’s Manual V2.69 © XIA 2015. All rights reserved.

  • Page 11: Setup Group

    At the bottom of the panel is a More button, which will make all advanced panel controls visible as well. The Pixie-4 being a digital system, all parameter settings are stored in a settings file. This file is separate from the Igor experiment file, to allow saving and restoring different settings for different detectors and applications.
  • Page 12 The pulse decay time Tau is used to compensate for the decay of a previous pulse in the computation of the pulse height. You can enter a known good value, or click on Auto Find Tau to let the Pixie-4 determine the best value. PIXIE-4 User’s Manual V2.69...
  • Page 13 For example, if the checkbox with pattern 0100 is checked, events with a hit in channel 2 and no others are accepted. Selecting multiple checkboxes accepts combinations of hit patterns, e.g. any event with exactly one channel hit. PIXIE-4 User’s Manual V2.69 xiii ©...
  • Page 14 Figure 3.4: The Run Control tab of the P Panel. ARAMETER ETUP PIXIE-4 User’s Manual V2.69 © XIA 2015. All rights reserved.
  • Page 15 ETUP are trigger distribution between modules, coincidence settings between modules, and the operation of the Pixie-4’s front panel input. See sections 7.2.2 and 7.6.2 for details. 3.2.4 Files/Paths The firmware files, DSP files and settings files are defined in the F panel.

  • Page 16: Run Control Group

    These panels are the MCA S display, the L display, the PECTRUM RACES display, the R , and a panel to display results from a series PECTRUM TATISTICS of files. PIXIE-4 User’s Manual V2.69 © XIA 2015. All rights reserved.
  • Page 17 Spectra can be saved as text files for import into other applications. 3.4.2 List Mode Traces and List Mode Spectrum Figure 3.7: The L display. RACES PIXIE-4 User’s Manual V2.69 xvii © XIA 2015. All rights reserved.
  • Page 18 TATISTICS The R panel shows the live times and count rates measured by the Pixie-4. The TATISTICS numbers can be updated by clicking the Update button and read from or save to Files. For a detailed description of the definition of these values, see section 6.6.

  • Page 19: Optimizing Parameters

    3.5 Optimizing Parameters Optimization of the Pixie-4’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 20: File Series

    This is equivalent to manually clicking first the Stop Run button and then the Start Run button. It is recommended to enable the automatic increment and auto- store options as shown in Figure 3.9 as well. PIXIE-4 User’s Manual V2.69 © XIA...
  • Page 21 The file series will thus contain spectra for a whole range of settings, which can be analyzed manually or with the routine described in section 3.6.3. PIXIE-4 User’s Manual V2.69 © XIA...
  • Page 22 Stop Run button. When the run is complete, click on the File Series button to open the panel described in section 3.6.3 3.6.3 File Series Analysis Figure 3.11: The F plot to analyze a series of files from a parameter scan. ERIES ESULTS PIXIE-4 User’s Manual V2.69 xxii © XIA 2015. All rights reserved.

  • Page 23: Data Runs And Data Structures

    MAXEVENTS can be decreased by the user if desired. MAXEVENTS can be set to zero, to disable the halting at a preset number. This makes the acquisition more efficient: if MAXEVENTS takes into account 4 “good” channels per event, PIXIE-4 User’s Manual V2.69 xxiii ©...
  • Page 24 The key difference is that as less data is recorded for each event, there is room for more events in the I/O data buffer of the Pixie-4 module and less time is spent per event to read out data to the host computer. For example, if you need individual energies and time stamps, but no waveforms, select run type “0x103 energy and time only”...
  • Page 25 MAXEVENTS = <calculate> (CHANHEADLEN = 2) MCA Mode Spectra in MCA block RUNTASK = 769 MAXEVENTS=0 4.1.3 Fast List Mode Runs The legacy “fast list mode runs” are no longer supported. PIXIE-4 User’s Manual V2.69 © XIA 2015. All rights reserved.

  • Page 26: Output Data Structures

    Word # Variable Description EVT_PATTERN Hit pattern. Bit [15..0] = [gate pattern | hit pattern | status | read pattern] EVT_TIMEHI Event time, high word EVT_TIMELO Event time, low word PIXIE-4 User’s Manual V2.69 xxvi © XIA 2015. All rights reserved.
  • Page 27 If N_WAVE_DATA is greater than zero, it indicates the number of waveform data words to follow. In the current software version, the XIA PSA value contains the result of the constant fraction trigger time computation (CFD). The format is as follows: the upper 8-bit of the word point to the ADC sample before the CFD, counted from the beginning of the trace.
  • Page 28 In the Pixie-4, there is a 48-bit time counter that is reset to zero at boot time or at a run start with the “synchronize clocks” option selected. It is incremented at the full processor clock rate of 75 MHz;...
  • Page 29 CHAN_TRIGTIME = 65100 and the event may be recognized after that at (EVT_TIMEHI, EVT_TIMELO) = (5467, 123). The correct absolute ChannelTime would be reconstructed from <BUF_TIMEHI>, 5466, and PIXIE-4 User’s Manual V2.69 xxix © XIA...

  • Page 30: Hardware Description

    0x100 and 0x101. 5 Hardware Description The Pixie-4 is a 4-channel unit designed for gamma-ray spectroscopy and waveform capturing. It incorporates four functional building blocks, which we describe below. This section concentrates on the functionality aspect. Technical specification can be found in section 1.2.

  • Page 31: Analog Signal Conditioning

    ADC. The anti-aliasing filter, an active Sallen-Key filter, cuts off sharply at the Nyquist frequency, namely half the ADC sampling frequency. Though the Pixie-4 can work with many different signal forms, best performance is to be expected when sending the output from a charge integrating preamplifier directly to the Pixie- 4 without any further shaping.

  • Page 32: Digital Signal Processor (Dsp)

    FIFO. 5.3 Digital Signal Processor (DSP) The DSP controls the operation of the Pixie-4, reads raw data from the RTPUs, reconstructs true pulse heights, applies time stamps, prepares data for output to the host computer, and increments spectra in the on-board memory.

  • Page 33: Pci Interface

    PCI slave IC together with an FPGA. The configuration of this PCI IC is stored in a PROM, which is placed in the only DIP-8 IC-socket on the Pixie-4 board. The interface conforms to the commercial PCI standard. It moves 32-bit data words at a time.
  • Page 34 (6.1) where the values of the weighting constants determine the type of average being computed. The sums of the values of the two sets of weights must be individually normalized. PIXIE-4 User’s Manual V2.69 xxxiv © XIA 2015. All rights reserved.
  • Page 35 } sets on a pulse by pulse basis. The Pixie-4 takes a different approach because it was optimized for high speed operation. It implements a fixed length filter with all values equal to unity and in fact computes this sum afresh for each new signal value k.

  • Page 36: Trapezoidal Filtering In The Pixie-4

    From this point onward, we will only consider trapezoidal filtering as it is implemented in the Pixie-4 according to Eqn. 6.2. The result of applying such a filter with Length L=1s and Gap G=0.4s to a -ray event is shown in Figure 6.3. The filter output is clearly trapezoidal in shape and has a rise time equal to L, a flattop equal to G, and a symmetrical fall time equal to L.

  • Page 37: Baselines And Preamplifier Decay Times

    Achieving this in the mixed analog-digital environment of a digital pulse processor is a non-trivial task, however. PIXIE-4 User’s Manual V2.69 xxxvii ©...

  • Page 38: Thresholds And Pile-Up Inspection

    Digital systems are much more efficient in this regard, since the values output by the filter are already digital values. All that is required is to take the filter sums, reconstruct the energy V and add it to the spectrum. In the Pixie-4, the filter sums are continuously updated by the RTPU PIXIE-4 User’s Manual V2.69...
  • Page 39 Figure 6.5: Peak detection and sampling in the Pixie-4. The peak detection and sampling in the Pixie-4 is handled as indicated in Figure 6.5. Two trapezoidal filters are implemented, a fast filter and a slow filter. The fast filter is used to detect the arrival of -rays, the slow filter is used for the measurement of V...
  • Page 40 Because the fast filter rise time is only 0.1 s, these -ray pulses do not pileup in the fast filter channel. The Pixie-4 can therefore test for slow channel pileup by measuring the fast filter for the interval PEAKSEP after a pulse arrival time. If no second pulse occurs in this interval, then there is no trailing edge pileup and the pulse is validated for acquisition.

  • Page 41: Filter Range

    6.6 Dead Time and Run Statistics 6.6.1 Definition of dead times Dead time in the Pixie-4 data acquisition can occur at several processing stages. For the purpose of this document, we distinguish three types of dead time, each with a number of contributions from different processes.
  • Page 42 FIFO write process was stopped, it takes a pre-trigger time to refresh the pre-trigger data and be ready for new events. To minimize this effect, the FIFO write process is stopped only G. Knoll, Radiation and Measurement, J Wiley & Sons, Inc, 2000, chapters 4 and 17. PIXIE-4 User’s Manual V2.69 xlii ©...
  • Page 43 FPGA. Therefore the soonest arrival time for a second pulse is at T3 after the FPGA readout is complete (now later than T4). The FIFO write resumes before T3, overwriting data already read out, and thus contains pre-trigger data for the second pulse at T3. 3. Coincidence window PIXIE-4 User’s Manual V2.69 xliii © XIA...
  • Page 44 In the current firmware, the FPGAs are released to resume data acquisition only after all channels marked in the hit pattern have been read out. At this time, all channels are cleared after readout, which means that pulses validated after the end of the coincidence window (and PIXIE-4 User’s Manual V2.69 xliv ©...
  • Page 45 FPGA. Please contact XIA for details. The MAXWIDTH parameter can be used to define a maximum acceptable time over threshold and thus to reject events piled up “on the rising edge”.
  • Page 46 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 live time counter, the last is counted separately. Fig. 6.10. The live time counter is stopped when the signal is out of range and when events are rejected because of a processing backlog in the DSP or spectrum memory increment process in the FPGA.
  • Page 47 In any case, burst rates are still limited by Poisson statistics (filter dead time) and the FPGA readout time, if it exceeds the filter time or if waveforms are read. 3. Gating or Veto (GFLT) PIXIE-4 User’s Manual V2.69 xlvii ©...
  • Page 48 The final type of dead time comes from the readout of data from Pixie-4 memory to the host PC. In MCA mode, this is limited to the access arbitration for the spectrum memory. The memory has only a single port for both the increments according to the pulse height computed PIXIE-4 User’s Manual...
  • Page 49 T0. In case c), the acquisition resumes already at T5 while the memory is read out independently. In a) and b), there is thus dead time in the Pixie-4 while it is waiting for the host to read out the data. In b) and c) there is dead time while the data is transferred to external memory.
  • Page 50 = F/(E+30ms) 6.6.2 Live and dead time counters The Pixie-4 firmware has been optimized to reduce the dead time as much as possible, and a number of counters measure the remaining dead times as well as the number of counts to provide information for dead time correction.
  • Page 51 ICR vs OCR and fitting with k*Td as a variable k, and so calibrate a dead time correction GDT (GATE dead time) PIXIE-4 User’s Manual V2.69 © XIA 2015. All rights reserved.
  • Page 52 GATE PULSEs, which are counted in the variable GCOUNT. 6.6.3 Count rates Besides the live and dead times, the Pixie-4 counts the numbers of triggers in each channel, FASTPEAKS, the number of valid events with one or more channels, NUMEVENTS, and the number of valid pulses stored for each channel, NOUT.
  • Page 53 Fig. 6.13 OCR and Livetime fractions of FTDT and SFDT as a function of ICR in a Pixie-4 measurement with a random pulse generator. The measured OCR follows the expected behavior from Eq.

  • Page 54: Operating Multiple Pixie-4 Modules Synchronously

    OCR, real time and dead time. In the Pixie-4, 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 55: Clock Distribution

    These jumpers differ slightly for modules of Revision B and Revision C/D. The clock functions themselves as described below are identical and compatible for both revisions. Pixie-4 Revision B JP1 JP2 JP1 JP2...
  • Page 56 2 or a backplane providing 37.5 MHz instead of the usual 10MHz. 7.1.1 Individual Clock mode If only one Pixie-4 module is used in the system, or if clocks between modules do not have to be synchronized, the module should be set into individual clock mode, as shown in Figures 7.1 (a) and 7.2 (a).

  • Page 57: Trigger Distribution

    Pixie-4 modules. Such a module can be a Revision C Pixie module configured as PXI clock master, shown in Figure 7.2 (f), a XIA PXI-PDM power and logic module, or any other suitable custom module. The PXI clock master has to be configured as shown in Figure 7.2 (f). The PXI clock slaves are configured by connecting pin 2 on JP1 and JP2 together (“PXI”...
  • Page 58 In other words, the backplane line carries a system-wide trigger that essentially acts as a 5 input to the trigger OR in the Communication FPGA of each module. PIXIE-4 User’s Manual V2.69 lviii © XIA...
  • Page 59 (Note: Sometimes there is no connection at all.) For applications with more than 7 modules, the Pixie-4 have to be operated in a chained OR mode, where trigger signals are passed from module to module using the PXI nearest neighbor lines which are not interrupted by the segment boundaries.

  • Page 60: Run Synchronization

    7.3 Run Synchronization It is possible to make all Pixie-4 modules in a system start and stop runs at the same time by using a wired-OR SYNC line on the PXI backplane. In all modules the variable SYNCHWAIT has to be set to 1. If the run synchronization is not used SYNCHWAIT must be set to 0. The variable is set by checking the corresponding checkbox in the Run Control tab of the Pixie Viewer.
  • Page 61 GATEBIT reflects the status of the GATE input at the time of the trigger either directly or after a coincidence window is applied. Names highlighted in green are controlled by the parameters in the Gate tab of the P Panel. ARAMETER ETUP PIXIE-4 User’s Manual V2.69 © XIA 2015. All rights reserved.
  • Page 62 Mainly due to the pipelined processing inside the ADC, it takes about 200 ns from a rising edge at the front panel analog input of the Pixie-4 until a trigger is issued by the Pixie-4 trigger circuit. The GATE signal starting the Gate Window counter is therefore delayed by ~200 ns inside the FPGA to compensate for this intrinsic delay.

  • Page 63: External Status

    The GATE signal is also distributed over the backplane, using 4 PXI nearest neighbor lines. Therefore a module to the left of a Pixie-4 can be used to input 4 GATE signals to the Pixie-4. XIA’s PDM can provide this function (inputs 8-5 for channel 0-3). The alternative is to use the VETO signal distributed to all modules and channels as the common GATE input for each channel.
  • Page 64 In any given event, a single Pixie-4 module will have up to four channels with a “hit”, i.e. a valid local pulse without pileup. The four channels thus form one of 16 possible Hit Patterns, stored in the lower 4 bits of a DSP parameter. In this representation, the Hit Pattern ranges from “no channel hit”...
  • Page 65 TOKEN line is left pulled up (3.3V, logic 1); else the TOKEN line is driven low (logic 0). The module in slot 2, typically XIA’s PXI-PDM module, uses the up to 48 bit hit pattern from up to 12 modules (slots 3-14) to make an accept/reject decision. If the hit pattern is acceptable, the TOKEN line is left pulled up.
  • Page 66 There is also a checkbox for each module to send the hit bit of its channel 3 to the status line. As the status line information is included in the event hit pattern in all modules, this allows one specific channel to contribute information to the event records of all modules. PIXIE-4 User’s Manual V2.69 lxvi ©...

  • Page 67: Using Pixie-4 Modules With Clover Detectors

    PDM] box is checked for all modules. Then check the "global test" box for all modules 8 Using Pixie-4 Modules with Clover detectors When working with clover detectors, the Pixie-4 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 –...
  • Page 68 The clover mode is enabled by setting the corresponding checkbox in the Pixie Viewer’s Module Control Register panel. There is also the option of binning only those events in the individual channel spectra that do not have multiple hits. Additional clover functions are under development. PIXIE-4 User’s Manual V2.69 lxviii © XIA...

  • Page 69: Troubleshooting

    9 Troubleshooting 9.1 Startup Problems 1. Computer does not boot when Pixie module is installed in chassis This is usually caused by an incorrect clock setting on the Pixie module. See section 7.1 for details. The module needs to have a valid clock to respond to the computer’s scanning of the PCI bus.
  • Page 70 XIA. 4. Drivers are installed, but module does not boot The Pixie-4 modules require driver version 6.5.0.0 provided by XIA, not the earlier versions (6.3.1, 5.2, 4.1 or 4.4). Modules should be listed in Window’s device manager as “PLX Custom (OEM) PCI 9054 Board (32)” or “ … (64)”. If the “PLX”...

  • Page 71: Acquisition Problems

    If the detector output shows significant ringing or overshoots, it can happen that the Pixie-4 triggers twice on the same pulse (first on the rising edge, then on the overshoot). This would be more likely for higher energy pulses, because the ringing or overshoot has a larger amplitude.
  • Page 72 8. Rate at which list mode data is written to file is low The number of events collected in a given time depends on a) the data per event, b) time required to record an event, and c) the data transfer rate. To reduce a), - run in compressed list mode (run types 0x101-103) - shorten the tracelength as much as possible (even in compressed list mode!)

  • Page 73: Front End Jumpers For Termination And Attenuation

    10.1 Front end jumpers for termination and attenuation Table 10.1: Analog conditioning selection jumpers on Pixie-4 modules. x=1..4 for channel 0..3. Jumpers are marked with solid red (50) and dashed blue (attenuation) arrows. Jumper PCB Label Function reference “ATTN” JPx01 Remove only if you require attenuation.

  • Page 74: Clock Jumpers

    Figure 10.1. Simplified input stage of Pixie-4 showing jumpers, input termination and attenuation, and the overvoltage protection circuit. 10.2 Clock Jumpers Table 10.2: On-board jumper settings for the clock distribution on Pixie-4 modules. Clock mode JP1 and JP2 PCB Label...

  • Page 75: Pxi Backplane Pin Functions

    10.3 PXI backplane pin functions Table 10.3: Pins of the J2 backplane connector defined in the PXI standard used by the Pixie-4. Pins not listed are not connected except for pull-ups to 5V recommended by the PXI standard. J2 pin...
  • Page 76 0x0001 Bit 0 RunEna Set to 1 to start data acquisition or 0 to stop. Automatically cleared when DSP de-asserts Active to end run. 0x0002 Bit 1 Unused Reserved for future use. 0x0004 Bit 2 PCIactive Set to reserve external memory I/O for host 0x0008 Bit 3 Unused...

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