The Pixie-4e is a multichannel data acquisition system for fast radiation detectors in nuclear physics and other applications requiring coincident radiation detection, and provides the following advantages:

  • Fast data transfer rates using PCIe
  • Sophisticated data acquisition
  • Advanced pulse shape analysis
  • Scalability; several modules can be combined into larger system




Based on the CompactPCI/PXI Express standard, the Pixie-4e is a 4-channel Digital Pulse Processor used in a variety of nuclear physics applications, including:

  • High-resolution gamma-ray spectroscopy
  • HPGe Segmented Detectors
  • Compton Background Suppression
  • Time-of-Flight measurements
  • Associated Particle Imaging

More about Applications…


Technical Data

Each of the four channels of the Pixie-4e module accepts signals directly from a detector preamplifier or photomultiplier tube. After a digitally controlled gain and offset state, signals are digitized in a 14 or 16 bit ADC at a rate of 500 or 125 MHz. Triggering, pile-up inspection, and filtering of the data stream is performed in real time; pulse heights and other event data is calculated on an event-by-event basis. Results are stored in 32K of spectrum memory per channel, and 256MB of list mode memory organized as a FIFO.

Pixie-4e modules can be controlled either by an in-crate single board computer or through a remote PCIe bridge by a desktop computer. XIA provides a set of C driver functions as well as a graphical user interface, the Pixie-Viewer, base on Wavemetric’s Igor Pro. Linux, LabVIEW, and ROOT demo code is available.


  • 125-500MHz, 12-16 bit ditizing of input sample
  • x4 PCI Express interface with module-to- host transfer rates of several hundred MB/s (interrupt driven DMA)
  • Simultaneous amplitude measurement and pulse shape analysis for each channel
  • Pulse heights measured with up to 16 bits accuracy on each of the four channels
  • Waveform acquisition up to 4K samples for each channel (8-32 μs)
  • 32K x 32bit on-board spectrum memory for each channel
  • 256 MB on-board FIFO memory for list mode data
  • Programmable gain, input offset, trigger and energy filter parameters
  • Coincident data acquisition across channels and modules
  • Triggers, run synchronization and clocks distributed over PXIe backplane
  • Online pulse shape analysis reporting sums over characteristic pulse regions (user defined)
  • Graphical user interface and C-based driver libraries
  • Operated through in-crate single board PC or through fiber optic link from desktop
  • Can be combined with commercial CompactPCI/PXIe processor, power, and computer modules
  • Customizable in hardware, firmware and software



Analog Four preamplifier inputs, switch-selectable input impedance:
50 Ohm or 2 kOhm. Not to exceed +/-3.5V if terminated with 50 Ohms and attenuation is not used. Optional 1/8 attenuation. Works with common resistive feedback preamplifiers of either signal polarity.
Digital (TTL 3.3V) Each module has a front panel MMCX connector which can be used to suppress data collection (Veto).

The Pixie-4e connects to the PXI and PXIe backplane lines, including bussed, nearest neighbor, star and differential star trigger lines. All clock, trigger and synchronization signals are distributed over these lines.

A high density front panel 10-pin connector can be used for I/O in custom applications

Data I/O

Interface PCIe standard, x4
Data Transfer Rate Memory readout to host: several hundred MB/s
Transfer Type Interrupt driven PCIe DMA transfers from Pixie-4e FIFO memory to host PC memory. FIFO buffer ensures uninterrupted acquisition of detector pulses up to the maximum transfer rate.

Digital Controls

Gain Coarse gain: 8 gain settings from 1.6 to 22.6
+/-10% digital gain adjustment for channel matching
(Gain steps and ranges may vary for digitization rates > 125 MHz)
Pulse amplitudes up to 1.25V (after termination) at gain=1.6
Proportionally lower at higher gain
Offset DC offset adjustment: -3V to +3V
Trigger Adjustable trigger filter to suppress noise
Filter length: 0.016 to 0.504 μs
Threshold range: 4 to 2000 ADC steps (after filter)
Filtering Trapezoidal filter with peaking times 0.048 to 63.4 μs
Adjustable flat top to eliminate ballistic deficit effects
Pileup Options to reject (default), ignore, exclusively accept piled up pulses which follow too closely to measure pulse heights individually
Coincidence Programmable coincidence window: 40 to 1016 ns
Reject unwanted hit patterns of the 4 channels
Data collection MCA limits and number of bins
Waveform lengths and pre-trigger delay

Data Outputs

MCA 1024 to 32,768 channels (32 bits deep) per Pixie channel
Additional memory for sum or 2D spectra
List Mode Time stamp, energy, optional waveforms for each event buffered in 256MB FIFO.
Timing Events are time stamped with ADC clock in list mode.
Statistics Livetime, runtime, input rate, output rate, filter dead time
Diagnostics ADC trace, baseline distribution, baseline history, FFT noise spectrum