National Instruments NI PXI-1042 Series User manual

STJ / MPX-32D
Quick Start Guide
Version 2.01
This document describes XIA’s instrumentation system for setting up an STJ system with one or more
MPX-32D 32-channel modular digital processors.

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CONTENTS
Contents ......................................................................................................................................................... 1
Overview of the System ................................................................................................................................. 3
MPX-32D Digitizer Module ......................................................................................................................... 3
Inputs and Outputs................................................................................................................................. 3
Banks and Channels................................................................................................................................ 4
Variable Gain .......................................................................................................................................... 4
Sample Rate............................................................................................................................................ 4
STJ Analog Module ..................................................................................................................................... 4
Preamplifier Schematic........................................................................................................................... 6
Inputs, Outputs and Controls ................................................................................................................. 6
STJ I/O Module ........................................................................................................................................... 7
Inputs, Outputs and Controls ................................................................................................................. 7
Custom Crate.............................................................................................................................................. 8
Inputs and Outputs................................................................................................................................. 8
STJ Input Connector (HDDSUB-78) Pinout.............................................................................................. 8
Quick Start Guide............................................................................................................................................ 9
STJ or Diagnostic Pulser Input?................................................................................................................... 9
System Setup .............................................................................................................................................. 9
Software Installation .............................................................................................................................. 9
STJ Preamplifier Installation ................................................................................................................... 9
PXI Crate Installation .............................................................................................................................. 9
Review PCI BUS Connections................................................................................................................ 10
EDIT the Configuration (INI) File ........................................................................................................... 10
Firmware (FDD) Files and Decimation .............................................................................................. 10
Start ProSPect....................................................................................................................................... 10
Using the ProSpect Software .................................................................................................................... 11
Overview of Typical Usage.................................................................................................................... 11
Channel Selection ................................................................................................................................. 12
Settings ................................................................................................................................................. 12
System Tab ....................................................................................................................................... 12
Auxiliary TAB..................................................................................................................................... 12
Detector TAB .................................................................................................................................... 14
Acquisition Tab ................................................................................................................................. 15
BiasScan Panel ...................................................................................................................................... 16
Set STJ Zero....................................................................................................................................... 17
Set STJ Bias ....................................................................................................................................... 18

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Scope Panel .......................................................................................................................................... 18
Measure the RC Decay Time............................................................................................................. 18
Adjust the ADC Offset....................................................................................................................... 20
MCA Panel ............................................................................................................................................ 20
Preset Run Constraint....................................................................................................................... 21
Statistics............................................................................................................................................ 21
Region of Interest (ROI) and Calibration........................................................................................... 22
GainMatch Panel .................................................................................................................................. 22
Mapping Panel: List-Mode Data Acquisition ........................................................................................ 23
List Mode Variant ............................................................................................................................. 23
Mapping Options .............................................................................................................................. 24
Acquiring List Mode Data ................................................................................................................. 25
Save the INI FIle!................................................................................................................................... 26

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OVERVIEW OF THE SYSTEM
The typical STJ system includes a cryostat with STJ detectors and associated control equipment provided
by a 3rd party combined with the following equipment provided by XIA:
•Commercial PXI interface and crate, containing:
oMPX-32D 32-channel digitizer module(s)
•Custom crate + ultra-low noise voltage regulators, containing:
oSTJ Analog 32-channel preamplifier module(s)
oSTJ I/O module, which includes an STJ input override switch
•Linear voltage supply module that provides power to the custom crate
•Associated interconnecting cables
MPX-32D DIGITIZER MODULE
XIA’s MPX-32D is a 32-channel digitizer and modular pulse-processor that resides in a computer-
controlled PXI crate. Its primary function is to measure pulse-heights, i.e. event energies.
Fig 1: MPX-32D 32-channel digitizer and modular pulse-processor
INPUTS AND OUTPUTS
Name Connector Type Description
Analog Inputs 0-15 SAMTEC
VRDPC-50-01-M-
RA
16 differential-pair analog inputs

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Analog Inputs 16-31 SAMTEC
VRDPC-50-01-M-
RA
16 differential-pair analog inputs
LVDS I/O Harting
27 21 121 8006
1 diff-pair analog output is driven by a 14-bit high-speed
DAC, i.e. the built-in pulser signal
3 LVDS digital outputs – used for communications and
STJ bias voltage DAC control
1 LVDS digital input – used for communications
PXI Backplane Standard PXI / CompactPCI 33MHz 32-bit interface
BANKS AND CHANNELS
The 32-channels are divided among 4 ‘Banks’ of 8 channels, each, due to the use of octal ADCs and octal
VGAs. Channels 0-7 comprise Bank0, Channels 8-15 comprise Bank1, Channels 16-23 comprise Bank2,
Channels 24-31 comprise Bank3. Note that some DSP parameters, e.g. BANK0ADCGAIN, BANK3ADCNYQ,
operate at the Bank level, and are thus duplicated 4 times with the Bank identifier (ranging 0-3) included
in the name.
VARIABLE GAIN
The analog signal gain passes through a software controlled octal variable-gain amplifier (VGA) stage. The
VGA is controlled at the Bank level by the DSP parameters BANK0ADCGAIN, BANK1ADCGAIN,
BANK2ADCGAIN and BANK3ADCGAIN.
The digitized signal can be approximately expressed in units of ADC least-signficant-bits (LSB) as:
ADC [LSB] = 10^((BANKnADCGAIN-5)/20) * input signal [mV]
For example, with BANK0ADCGAIN = 20, a 100 mV signal on channels 0-7 yields an ADC amplitude of
approximately 576 LSBs. Note that the STJ Analog transimpedance gain is 1 mV/nA, so the gain can also
be expressed as:
ADC [LSB] = 10^((BANKnADCGAIN-5)/20) * STJ signal current [nA]
SAMPLE RATE
The on-bard octal ADC’s digitize the preamplifier signals at 50 MS/s, i.e. the sampling interval is 20 ns.
ENERGY SCALING
Digital trapezoidal filtering is used to improve the signal-to-noise in order to optimize the energy
(amplitude) measurement. The filter includes a fine-grain digital scaling factor
Needs work!!!
Note that analog variable gain and digital scale factor are controlled in ProSpect via the Preamp Gain,
Dynamic Range and MCA Bin Width settings…
STJ ANALOG MODULE

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XIA’s STJ Analog module is a 32-channel preamplifier card, with an associated software-controlled STJ bias
voltage DAC and input connection relay for each channel. A backplane diagnostic pulser signal is routed to
each channel via a separate relay.
Fig 2: STJ Analog 32-channel preamplifier card

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PREAMPLIFIER SCHEMATIC
The basic preamplifier circuit is shown below. The primary feedback elements are a 1 MΩresistor (which
yields the transimpedance gain = 1 mV/nA) in parallel with a 1 pF capacitor. A secondary low-frequency
feedback loop maintains the software-selected bias voltage at the STJ input. Each preamplifier circuit
includes an STJ Input Relay, which connects its input to either the STJ detector or a local ‘dummy
detector’ resistor-capacitor network (10 kΩin parallel with 2 nF). All 32 channels share the Pulser Relay,
which connects their inputs to the diagnostic pulser signal via per-channel 10 MΩresistors.
Fig 3: STJ Analog front-end schematic
INPUTS, OUTPUTS AND CONTROLS
Name Connector Type Description
Analog Outputs 0-15 SAMTEC
VRDPC-50-01-M-
RA
16 differential-pair preamplifier outputs
Analog Outputs 16-31 SAMTEC
VRDPC-50-01-M-
RA
16 differential-pair preamplifier outputs
LVDS I/O Harting
27 21 121 8006
1 diff-pair analog input is received as a pulser input
3 LVDS digital inputs – used for communications and STJ
bias voltage DAC control
1 LVDS digital output – used for communications
Custom Backplane Eurocard The backplane connector carries the STJ input signals,
power supply connections and the user pulser signal
Pulser selection
jumpers
2x3 2mm header +
2 jumpers
The header and jumpers comprise a DPST switch to
select either the software-controlled pulser signal from
the MPX-32D or a user pulser input connected via the
STJ I/O card. See photos below for jumper configuration

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The jumpers at location J400 are set by default, as shown at left below, to connect the preamplifiers to
the built-in diagnostic pulser from the MPX-32D module via a software-controlled relay. To select the user
pulser input connected to the STJ I/O front-panel SMA connector, move both jumpers towards the
backplane connector, as shown at right below.
Fig 4: STJ Analog pulser selection jumpers
STJ I/O MODULE
XIA’s STJ I/O module must be installed in the left-most slot of the custom crate. It provides a “kill” switch
that overrides the software-controlled relay connection between the STJ detectors and the preamplifier
inputs, as well as the user pulser analog input and a diagnostic ‘channel 0’ output for each STJ Analog
module installed.
INPUTS, OUTPUTS AND CONTROLS
Name Connector Type Description
“Kill” switch Toggle switch Left-hand position: overrides software control of STJ
input relays—STJs are disconnected!
Right-hand position: software controls STJ input relays
Channel 0 Outputs SMA (x4) A single-ended version of the channel 0 preamplifier
output signal from each STJ Analog card in the custom
crate is routed to an SMA output connector for
diagnostic purposes.
User Pulser Input
SMA The bottom-most SMA connector accepts a user-
provided diagnostic pulser input that can be routed to
all preamplifiers in the crate via software-controlled
relays. The input is terminated to ground with a 50
Ω
resistor. Note that the STJ Analog pulser selection
jumpers must be configured properly, as described
above.

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CUSTOM CRATE
XIA provides a custom crate designed to house up to four STJ Analog modules (up to 128 STJ detector
channels) and the STJ I/O module.
INPUTS AND OUTPUTS
Name Connector Type Description
HDDSUB-78 x4 HDDSUB-78 (x4) 4 rear-panel connectors each provide connections for to
up to 32 STJ detectors (see pinout below). Each
connector corresponds to one of the four STJ Analog
slots, in the same order. Note that XIA does not provide
HDDSUB-78 cables to connect the custom crate to the
STJ detectors in the cryostat. The cable should be
shielded and as short as possible.
Custom Backplane Eurocard (x5) 4 backplane connectors each carry the STJ input signals
from one HDDSUB-78 connector, power supply
connections and the pulser input to an STJ Analog
module. A fifth slot (left-most) is reserved for the STJ
I/O module.
Power input Circular The circular connector on the bottom of the chassis
connects power from the linear voltage supply module
STJ INPUT CONNECTOR (HDDSUB-78) PINOUT
Fig 5: STJ input connector (HDDSUB-78) pinout

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QUICK START GUIDE
STJ OR DIAGNOSTIC PULSER INPUT?
The STJ Analog preamplifiers accept inputs both from the STJ detectors and from a diagnostic input, which
is connected to either the built-in software-controlled pulser or a user-provided signal. We recommend
starting with the built-in pulser to first familiarize the user with the software, settings and data acquisition
procedures. This approach bypasses the complex tasks of biasing the STJ detectors and solving system
grounding and signal integrity issues. Without proper biasing and grounding, the input signals can do
unexpected things.
SYSTEM SETUP
SOFTWARE INSTALLATION
Run the provided ProSpect executable and follow the steps as indicated within the installer.
STJ PREAMPLIFIER INSTALLATION
The custom crate should be connected to detector cryostat via HDDSUB-78 cables (not provided) and a
solid ground connection, and to the power supply using the provided power cable with circular
connectors. It is critical to make a solid ground connection between the custom crate and the detector
cryostat, and to otherwise isolate the two from other ground connections. Ideally the two pieces of
hardware are physically co-located and bolted together. If that’s not possible a thick copper braid may be
sufficient.
•Signal integrity issues almost always trace back to poor grounding between the custom crate
and the detector cryostat, or improper STJ wiring within the cryostat itself.
•The custom crate can safely be powered on/off and connections can safely be made while the
PXI crate is powered
Each STJ Analog card in the system should be installed into one of the four right-hand slots in the custom
crate, and connected to its corresponding MPX-32D via 2 Samtec cables and 1 Harting cable.
•Samtec front-panel connectors are labeled “0-15” or “16-31”. Make sure that every Samtec
cable is connected such that the labels on each end are consistent.
PXI CRATE INSTALLATION
Turn off the PXI crate. Install the required number of MPX-32D modules, power on the PXI crate
connected to the host computer and then re-boot the host computer. After Windows starts you should
get a notification and prompt to install new drivers for each and every MPX-32D module. This is tedious,
but you should only have to do this the first time a slot is occupied.
•ALWAYS power off the PXI crate before installing or removing MPX-32D cards!
•Turn on the PXI crate, then re-boot the computer

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REVIEW PCI BUS CONNECTIONS
Open the Windows Device Manager (right-click on My Computer, select Manage, and then select Device
Manager in left panel) and scroll down to and expand the Other Devices section. There should be a “XIA
MPX-32D Digitizer and Pulse Processor” entry for each MPX-32D module in the connected PXI crate(s).
Double-click on an entry to view the PCI Bus and Slot assignments for that module. It is important to
identify the assignments for each module so that its identity in the software can be associated with its
physical location in the array.
Note that larger PXI crates will contain multiple PCI bus segments, and that the slot assignments are often
not very intuitive: The ordering is typically backwards compared to the labels on the PXI crate.
•Note the PCI bus and slot numbers for your system
EDIT THE CONFIGURATION (INI) FILE
You should receive a sample configuration (INI) file. Open the file with a text editor and find the entries
for pci_bus and pci_slot towards the end of the file. These values MUST match the device settings for your
system. See the “Review PCI Bus Connections” section above.
•Edit the pci_bus and pci_slot values as necessary and save the INI file.
•Save the INI file frequently as settings are adjusted, and note that you can also save and
retrieve to/from different INI files
You can also use the Generate Configuration File dialog, accessible under the Tools menu, to generate a
new INI file and view compatible XIA modules detected on the PXI bus.
FIRMWARE (FDD) FILES AND DECIMATION
XIA provides three different firmware (FDD) files, with Decimation values 0, 1 or 2. Decimation sets the
base units of the energy filter, and thus the Peaking Time + Gap Time range. We typically recommend
using Decimation 0. To use Decimation 1 or 2, i.e. longer peaking times, change the “filename” path(s) in
the [firmware definitions] section of the INI file.
FDD File Decimation Base Units Peaking Time + Gap Time Range
stj_decimated0_45T.fdd 0 20 ns 100 ns – 20.48 µs
stj_decimated1_45T.fdd 1 40 ns 200 ns – 40.96 µs
stj_decimated2_45T.fdd 2 80 ns 400 ns – 81.96 µs
Table 1: Decimation and Peaking Time Range
START PROSPECT
When ProSpect is started the first time, you will be prompted to select an initialization file. Please browse
to and select the edited INI file. Thereafter, on startup ProSpect will automatically select the most
recently used INI file.
Note: It is almost always necessary to re-boot the host computer whenever power is cycled on the PXI
crate. Always turn on the PXI crate before starting the host computer.

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USING THE PROSPECT SOFTWARE
ProSpect is a Windows application that runs with XIA’s Handel drivers. It is primarily intended as a
platform for system configuration, but ProSpect can also be used to acquire and save data.
Fig 6: ProSpect is organized into three main areas: Channel Selection, Settings and the Data Panel.
OVERVIEW OF TYPICAL USAGE
Once the STJ bias voltages, gain, thresholds and other settings have been optimized and saved to an INI
file as described in this document, the typical usage is:
1. Power on the PXI crate, STJ detectors and preamplifiers, and then wait for preamplifiers to settle,
as indicated by the green LED on the custom crate
2. Start ProSpect or initialize the system by selecting your modified INI file
3. Optionally verify the STJ biasing by running a BiasScan operation and inspecting Fiske Mode
locations vs bias voltage settings for all channels.
4. Optionally verify the presence of input pulses and the Decay Time setting by acquiring ADC traces
with the Scope tool.
5. Optionally calibrate the gain using the GainMatch tool
6. Adjust the ADC Offset – this must always be done after the system is initialized and/or gain is
modified, e.g. during calibration.
7. Acquire data in MCA mode or Mapping/List mode using ProSpect or XIA’s Handel drivers via
custom software
8. Analyze data using 3rd party or custom software

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CHANNEL SELECTION
The Channel Selection tool applies to all panels and tools. The “Apply to All” check-box ensures that any
changes to settings are applied to all modules in the system.
•Make sure the “Apply to All” check-box is checked!
SETTINGS
Most settings, or acquisition values, are located in the Acquisition, Detector, and Auxiliary tabs in the left
panel. Some settings are only accessible via the DSP Parameters panel, which can be opened via the Tools
menu. The following sections contain very brief descriptions of the primary settings. For a more detailed
explanation of XIA’s approach to digital pulse processing and associated settings, please refer to:
•microDXP Development Kit Manual
•microDXP Technical Reference Manual
SYSTEM TAB
Before changing settings, however, let’s take a look at the System tab. The upper section displays the
MPX-32D modules in the system and their PCI assignments. The lower selection displays the channels in
the selected module.
The primary use for the System tab in this application is the enabling and disabling of channels, performed
by clicking in the Disable column adjacent to each channel. When a channel is disabled, data acquisition
will be disabled for that channel, which reduces communications and processing overhead. Channels that
aren’t wired to actual STJ pixels, for example, can and should be disabled. The channel enable/disable
settings can be saved to the INI file, such that the state of the system is restored whenever the system is
initialized.
AUXILIARY TAB
This panel displays the auxiliary Analog Module status and contains the STJ Relay and Pulser controls.
ANALOG MODULE
The first section displays whether an auxiliary Analog Module has been detected (properly connected to
the currently selected MPX-32D module and powered on), the type of auxiliary module and its firmware
revision. This information can be used to verify your system setup. The images below show the Auxiliary
tab with an STJ Analog card, aka “Analog Module”, with revision 0xCD02 detected. If no module is
detected, first check your cable connections and power, and then try pushing the Enable/Disable button.
When the button transitions from green to red, the system polls the module status.

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Fig 7: The Auxiliary tab with an STJ Analog auxiliary module connected to the currently selected MPX-32D module.
STJ RELAY
The most important setting on this panel is the STJ Relay Enable/Disable button. By default, STJ Analog
on-board relays are open (as shown above): The STJ detectors are terminated with 1MΩresistors, and the
preamplifier inputs are terminated with 10kΩresistors in parallel with 2nF capacitors, i.e. a ‘dummy’
detector circuit. When the relays are closed/enabled, the preamplifier inputs are connected only to the
HDDSUB-78 pins, i.e. to the STJ detectors, if present. We recommend first familiarizing yourself with the
system by using the on-board pulser to generate an input signal before working with actual STJ detectors
(see below). Note that if the STJ detectors are not connected the HDDSUB-78 connector(s), the STJ Relay
provides a convenient ‘low noise’ pulser setting: the pulser signal is much cleaner when the dummy
detector circuit has been removed via the relay.
•The “kill” toggle switch on the analog chassis prevents the STJ relays from closing when in the
left-hand position. Make sure this switch is in the right-hand position.
•Click the STJ Relay Enable/Disable button so that it changes from green to red. Note that the
LED on the analog chassis corresponding to the selected STJ Analog module will change from
solid green to solid red when the relays are closed.
PULSER
The Pulser Settings control a rudimentary built-in pulser circuit, which feeds a periodic signal to all
preamplifier channels on the Analog Module. The signal is generated by a DAC on the MPX-32D which
repeatedly cycles through 4K points of waveform data stored in RAM. It is quite useful for debugging and
for exercising the data acquisition system. After system initialization the Pulser Enable/Disable button
should be green (as shown above), indicating that the pulser is turned off.
•Press the button to enable the pulser, keeping the default settings as shown, which generates
a periodic pulse with a 1 µs risetime and 5 µs decay time, at 1 kHz frequency.
•The PULSEGAIN setting coarsely controls the pulse amplitude, which is proportional to
2^PULSEGAIN. Valid PULSEGAIN values ranges from 0 to 3.
•The PULSERINVERT setting controls the polarity of the pulse waveform. It should be set to 0 or
1 such that pulses are positive in the ADC waveform, as viewed in the Scope panel.

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•The PULSERATE setting controls the rate at which the DAC is updated: update rate = 20 ns *
2^PULSERATE. Note that this setting affects the rise time and decay time! With the default
value 0, the waveform spans 80 µs, with a 1 µs risetime and 5 µs decay time. With
PULSERATE=1, the waveform spans 160 µs, with a 2 µs risetime and 10 µs decay time, etc.
•The PULSEWAIT setting, ranging from 0 to 255, controls the time that the circuit waits before
cycling back to the beginning of the waveform data, i.e. it can be used to reduce the count rate.
Its units depend on PULSERATE: wait time = 256 * update rate as defined above. For example,
with PULSERATE=0, the units are 5.12 µs.
Now proceed to the Scope Panel section below to explore the Decay Time setting in the Detector tab.
When you are ready to connect to actual STJ detectors, you will typically want to disable the pulser. Note
that it is safe to enable the pulser while the STJ Relay is closed, in case you want to combine the periodic
signal with the detector signal.
DETECTOR TAB
The Detector Settings need to be edited. Start by first setting the Polarity and Preamp Gain to these
recommended settings:
•Set the Polarity to “-“
•Set the Preamp Gain to “150.000 mV/keV”
POLARITY
For a positive STJ bias voltage, the Preamplifier: Polarity setting should be “-” (negative), and vice versa.
When the polarity is set correctly, ADC pulses should be positive as viewed in the Scope panel.
DECAY TIME
When using STJ detectors, the preamplifier Decay Time can only be determined after the STJ bias voltage
has been set and x-rays are present. In our experience the Decay Time ranges from a few 10’s to 100’s of
microseconds, depending on the detector. It can be measured directly using the cursors in the Scope
panel (with Trace Type = ADC, Trigger Type = Threshold). Note that the Sampling Interval can be adjusted.
The minimum value is 20 ns, corresponding to the 50 MHz ADC clock. The trace buffer is 4000 points,
yielding an 80 µs waveform with the minimum Sampling Interval. You may need to increase the Sampling
Interval for longer decay times.
•When using the built-in Pulser, the Decay Time should be set to 5.0 µs * 2^(PULSERATE). For
example, with PULSERATE=0 (default), it should be set to 5.0 µs.
PREAMP GAIN
The Preamp Gain setting, along with the Dynamic Range setting on the Acquisition tab, determines the
MPX-32 analog and digital gain settings. The exact relationship is a bit convoluted, due to the fact that
each bank of 8 channels share the same analog gain setting due to hardware limitations.
•We recommend starting with a value of 150 mV/keV along with a 2 keV dynamic range, and
then using the ROI Calibration tool and/or the GainMatch tool to refine the Preamp Gain
setting on a per-channel basis.

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•Note that with these settings, the built-in pulser (with default settings as shown in Figure 7)
should generate events with energy roughly equal to 1 keV and a count rate of 1 kcps.
ACQUISITION TAB
The Peaking Time and other Filter Parameter settings control the trapezoidal digital filtering algorithms.
At minimum, the Peaking Time, Gap Time and Trigger and Energy Thresholds should be optimized for each
system. For a thorough explanation of these settings please refer to Chapter 4 of the microDXP Technical
Reference Manual.
PEAKING TIME
The Peaking Time control sets the integration time of the slow energy filter. In the past we have gotten
the best results with Tantalum STJ’s when the Peaking Time is in the range 16 to 18 microseconds, with a
Gap Time of 4 to 6 microseconds. These settings are best adjusted after the STJ bias voltage has been set.
•Make sure the “Apply to All” check-box is checked!
•Edit the value in the Peaking Time field and press the Apply button.
Note that these recommended settings are close to the maximum supported for Decimation 0. If the
desired Peaking Time + Gap Time is greater than 20.48 µs, you will need to change the firmware filename
path in the INI file to select Decimation 1 or 2, as described in the Firmware (FDD) Files and Decimation
section above.
THRESHOLD
The STJ processing pipeline includes two separate digital filters: Trigger (fast) and Energy (slow). The
trigger filter output is optimized for speed, and is used exclusively to detect input pulses and pileup. The
slow energy filter is optimized for noise reduction. It is used primarily for energy measurement, but can
also be used to detect very small pulses, i.e. low energy events, but it doesn’t do a very good job at pileup
detection.
•When running with actual STJ detectors, the STJ bias voltage should be optimized set properly
before attempting to optimize threshold settings!
•Thresholds may need to be re-optimized after the gain is modified (either directly or via the
Calibration or GainMatch tools)
•The Trigger Threshold should always be enabled, i.e. non-zero. It should be optimized first, with
the Energy Threshold disabled, i.e. set to 0. If the gain is set properly, the fast threshold can
typically be set below 100 eV. The value can be optimized by acquiring MCA data in short runs
and looking for a noise peak near 0 eV. If the threshold is too low, a noise peak will appear and
the input count rate will measure higher than expected. The optimal threshold is set just above
the value that generates a noise peak.
•The Energy Threshold can be enabled to extend detection of events to lower energies, and
should only be used in combination with a non-zero Trigger Threshold. After the Trigger
Threshold has been optimized, set the Energy Threshold to the lowest value that does not
generate a noise peak.

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MCA
These settings control the output scaling of the energy measurement, which correspond to the X-axis
scaling and granularity in the MCA panel.
•We recommend always using the maximum Number of Bins: 8192 bins
•We recommend using MCA Bin Width = 0.25 eV/Bin with a 2 keV Dynamic Range. If you are
interested in energies above 2 keV, increase both of these settings by factors of 2, e.g. 0.50
eV/Bin with 4 keV Dynamic Range, etc.
BASELINE
The Baseline Average setting determines the number of samples in the running baseline average.
•We recommend always using the default value: 256 Samples, unless otherwise instructed by
XIA
ADVANCED SETTINGS
Additional acquisition settings are accessible in the Edit Filter Parameters dialog, including the slow filter
Gap Time, the Peak Capture method and Fast Trigger Filter settings. Please refer to the microDXP
Technical Reference Manual for more details about these settings.
•Press the Edit Filter Parameters button to edit the advanced acquisition settings
•Edit the Gap Time such that the value comfortably exceeds the rise time of incoming pulses as
viewed in the Scope panel. Note that the maximum Peaking Time plus Gap Time are
constrained by the Decimation, i.e. firmware (FDD) file, as described in the Firmware (FDD)
Files and Decimation section.
•We recommend always using the Peak Sensing Capture Method! This means that the largest
energy value within an appropriate window is recorded, which always yields the optimum
energy resolution. With the Peak Sampling method, you will need to adjust the Peak Sampling
Time to achieve optimal energy resolution.
•We recommend setting the Fast Trigger Filter Peaking Time to 1.000 µs for most STJ systems,
which achieves a good balance between speed and noise rejection.
•The Max Width setting controls pileup rejection in the Fast Trigger Filter: pulses that remain
over threshold for longer than this interval are rejected. This setting should normally be set to
a conservative 10 µs. For high count rates (>100 kcps), you may want experiment with reducing
this value to reject events that pile up in the Fast Trigger Filter.
BIASSCAN PANEL
The BiasScan panel is used to plot the STJ I-V curve in order to select a bias voltage for the detector. When
the “Start Scan” button is pushed, the bias voltage for each STJ detector is set to the “Starting Offset”
value, then the voltage is incremented across the prescribed voltage range. At each increment the output
voltage and signal noise level are measured. The output voltage is proportional to the detector current. It
is plotted in green, with arbitrary units on the left-hand y-axis (Note that we intend to update the
software with y-axis units in Amperes). The noise level is plotted in arbitrary units on the right-hand y-
axis.

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Fig 8: The BiasScan panel acquires and displays the STJ I-V curve. The cursors are used to set the zero-point and bias voltage.
Here are the typical settings used in our prior work with Tantalum STJ detectors:
•Starting Offset = -500 µV
•DAC Stepsize = 1 µV
•Scan Points = 500 (a good balance between resolution and time required)
•Wait Time = 50 ms
With the settings above, the scan starts at -500 µV and increments 1000 times by 1 µV, i.e. terminating at
+500 µV, and waiting 50 ms between each increment for the voltage to settle. Reducing the Wait Time
directly reduces the time required for the scan. In the past we typically reduced the Wait Time when
doing a ‘sanity check’ bias scan, and increased it when doing careful measurements.
•Press the Start Scan button and wait for the run to complete. The run time depends primarily
on the number of Scan Points and the Wait Time.
By default, the green bias current plot is selected. Click and drag in the plot to quickly zoom. Click and
drag on any of the axes to quickly pan. Right-click and select “Full Scale” to zoom all the way out. To zoom
in on the red noise plot, first right-click and select “Zoom Reference”, then click and drag as before.
There are two vertical cursors in the plot. The blue cursor is used to set the STJ Zero, and the yellow
cursor is used to set the STJ Bias voltage, as described below.
SET STJ ZERO
Because of imperfections in ground connections, and the DAC and associated electronics, there is an
offset voltage associated with the DAC zero-point, i.e. when the DAC is set to 0V, the STJ detector may in
fact be biased with a few 10’s of micro-Volts. The inflection point in the characteristic STJ I-V curve is used
to find the actual DAC setting that corresponds to 0V at the STJ detector. Drag the blue cursor to the

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centroid of the inflection point in the green (bias current) plot. Note that the value in the Zero Adjust
changes with the cursor selection, and is highlighted yellow if the value is different from the saved STJ
Zero.
•Move the blue cursor to the inflection point in the green plot, then press the “Set STJ Zero”
button.
•Repeat for all channels!
•Press the Start Scan button again to acquire new data with the voltage offsets removed. Note
that the inflection point should now be centered along the x-axis, at 0V.
•In the past we have had to repeat this entire process a few times to get the offsets set
properly. This may have been necessary because of faulty ground connections that led to
interactions between the STJ pixels.
SET STJ BIAS
The STJ bias should be chosen in the appropriate voltage range, and at a voltage that is not associated
with a Fiske-mode peak. The noise level plot is useful for identifying the Fiske-mode peaks.
•Move the yellow cursor to the desired voltage, then press the “Set STJ Bias” button.
•Repeat for all channels!
At this point, all of the STJ detector elements should be properly biased.
SCOPE PANEL
The Scope panel displays raw ADC and filter data for debugging purposes. Data acquisition occurs
simultaneously for all channels in the currently selected modules. We strongly recommend reviewing this
section before trying to acquire MCA or list-mode Mapping data.
•Set the Trace Type to “ADC”
•Set the Trigger Type to “Threshold”
•Turn on the x-ray source, or alternatively, enable the pulser in the Auxiliary tab
•Press the Get Trace button to simultaneously acquire a plot of the ADC for all 32 channels
•You may need to adjust the Trigger Threshold (in the Acquisition tab) to properly trigger the
acquisition. Note that the hardware times out after a second or so if no trigger is generated,
and just acquires un-triggered data.
MEASURE THE RC DECAY TIME
You should see positive RC decay pulses in the ADC data (either from the on-board pulser or from the
detector). To get the best energy resolution, the Decay Time setting in the Detector tab must be set
properly. Use the cursors in the ADC plot area to measure the decay time τ. Note that energy resolution
can be degraded significantly if this setting is way off, but small errors won’t really affect the data quality:
Don’t worry about getting it exactly right. For a more thorough explanation of the measurement, please
review section 3.8.3.4 of the microDXP Development Kit Manual, noting that the signal rise time is
typically much longer for STJ detectors than for conventional x-ray detectors, e.g. silicon drift.
•If you’re using the pulser, the Decay Time is 5 µs (with PULSERATE=0)

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Fig 9: The Scope panel showing a pulse from the built-in pulser (with default settings), with the Polarity set correctly
As a check, change the Trace Type to Scaled Energy and acquire more traces. The output of the energy
filter should be a trapezoid with slightly curved edges. If there is significant over-damping or under-shoot
after the pulse, the Decay Time is set too low. If there is significant under-damping or over-shoot after the
pulse, the Decay Time is set too high.