GLAST Large Area Telescope
Gamma-ray Large
Area Space
Telescope
Engineering Meeting
23 November 2004
Charge Injection Calibration
James Swain
Stanford Linear Accelerator Center
[email protected]
650-926-2721
Goal
• To gather enough information to produce
– DAC -> ADC curves for each discriminator in the front ends
– Measurements of cross-talk between front end channels
– Time over threshold curves
• Need subsystem input
– How should we collect TOT data? One channel at a time?
– What pulse patterns do we need to make available?
• FSW is proposing providing two pulse patterns, each of
which can optionally be masked
23 November 2004
Engineering Meeting - Charge Inj. Calibration
2
Operation
• Configure
– Use LATC to perform initial configuration.
– Perform reconfiguration (DACs, thresholds etc) within
calibration loops as determined by LCI configuration files.
• Pulse
– Number of times determined by LCI configuration files
• Read
• Accumulate
• Package
– Preserve as much of the raw data as possible.
• Send
• Don’t Analyse
• Don’t Apply
23 November 2004
Engineering Meeting - Charge Inj. Calibration
3
Calibration Styles
Subsystem
Calibrations
ACD
PHA (ADCs)
CNO
Accepts
Hits
Pedestals
CAL
TKR
23 November 2004
Bit scan
ADC scan
X
X
X
X
X
ADCs
Low Energy Trigger
High Energy Trigger
Accepts
Pedestals
X
X
X
X
X
Accepts
Time over Threshold
X
X
Engineering Meeting - Charge Inj. Calibration
4
Calibration Styles (cont’d)
• Bit scan
– For charge injection DAC setting
– For each of threshold setting
– Pulse N times and record the number of accepts.
• Simple version just uses a fixed number of DAC settings
• Intelligent version focuses around the interesting
threshold region.
• ADC scan
– Fixed number of injection DAC settings
– Record ADC response to injection N times.
23 November 2004
Engineering Meeting - Charge Inj. Calibration
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Volume and Time Estimates
Subsystem
Projected
Time
Uncompressed
Volume
Compressed
Volume
CAL
10 s
420 Mbits
150 Mbits
TKR
640 s
8 440 Mbits
420 Mbits
ACD
10 s
30 Mbits
10 Mbits
• Assumptions
– Pulsing at 10 kHz
– Pulsing 1 channel per TFE, 12 TFE per TRC
• Cross-talk measurements will take longer
– Auto-range readout for the CAL
• Intend to use auto-ranging for most of the DAC values
• Use four-range readout for overlap regions and keep two
ranges so the overlap regions will increase data volume
23 November 2004
Engineering Meeting - Charge Inj. Calibration
6
FSW needs
• What results would FSW like to be uploaded after calibration?
– ACD pedestals
• Might be nice, but not necessary
– CAL linear correction
• Two values per range per log end required.
23 November 2004
Engineering Meeting - Charge Inj. Calibration
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