iTOP LEPS Beam Test Analysis
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Transcript of iTOP LEPS Beam Test Analysis
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iTOP LEPS Beam Test Analysis
LYNN WOOD
JULY 17, 2013PACIFIC NORTHWEST NATIONAL LABORATORY
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Topics
LEPS Beam Test Summary
iTOP Electronics OverviewIRS3B ASIC
CorrectionsVoltageTiming
Current Analysistopcaf (software)Results
Next Steps
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LEPS Beam Test – June 4-20, 2013
Goal: end-to-end test withFull quartz bar including mirror and prismFull bar of PMTs and ASIC-based electronicsBelle II DAQ-based readout (COPPER)
Facility: LEPS beamline at SPring-82 GeV photon beams generated by backward Compton scattering of UV laser photons off 8 GeV synchrotron ring electronsPhotons strike Pb target, produce e+/e- pairs that pass through detector
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LEPS Configuration
e+ beam trigger from four countersg rate: 30 kHzTrigger rate: 10 HzDAQ rate: 5 Hz
Timing available from acceleratortiming signals: ~24.3 ps
Data taken at multiple angles of incidence and locations:
Cos q = 0 (normal to bar)Cos q = 0.39, x = 0cmCos q = 0.37, x = 20cm
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iTOP Electronics Overview
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Physical Layout
One SCROD
One ASIC
One carrier board
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ASIC Block Diagram
Per channel:Single input128 sampling cells (capacitors)256 transfer cells32768 storage cells64 counters for digitization
Per ASIC:Timing generatorRamp generator (for digitization)
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Uncertainties
In the ASIC:Voltage uncertainties
Comparator response (32768 x 8 per channel)ADC counter rates (64 per channel)Response of sampling array (128 x 8 per channel)
Possible difference in DC vs. AC responseInput coupling and signal frequency content
Timing uncertaintiesOverconstrained timing – overlap/gap between recordsVarying delays from sample-to-sampleBias voltage (and noise on bias voltage), temperature driftFeedbacks cannot currently compensate for small drifts
Outside the ASIC:Clock shared in “columns” across boards – currently unterminated tracesPath length differences in FPGA for different ASICs Crosstalk between channels
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Comparator Response
ADCs are Wilkinson-style ramp comparators
Fires when ramp exceeds stored voltageSignals stored with DC offset to fit into ADC’s dynamic range
Offset varies cell-to-cell = pedestal correction
Comparator response is nonlinearTransfer function varies for each storage cell
Examples here from IRS2 and TARGET5 ASICs (same comparator as IRS3B)
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AC vs. DC response
Transfer functions measured with DC inputs, but AC response may be differentOne example: persistence
Voltage has some dependence on previous-stored voltageWill show “ghost” pulse for 1+ cyclesWill also reduce pulse heightShould primarily affect large pulses
Example from PSEC3 chip at right
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Input Coupling
Multiple components:Amplifier bandwidthCoupling into ASIC sample cells
Can depend on timing parameters of ASIC – how many sampling cells are currently connected
Definite apparent gain in pulser data, but spectral content differs between laser and pulser data
Corrections not the sameHard to measure gain without fixed-height samples
Need calibration signals that look like MCP-PMT signals!
Laser Pulser
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Overconstrained Timing
Timing within each 128 samples controlled by delay lineTiming controlled by bias on delay lineEach 128 sample set started with input clock
Incorrect biasing may end sample too soon (gap between samples) or too late (overlap between samples)
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Sample-to-Sample Timing Uncertainties
Delay lines stages can have varying delays between them
Has strong impact on timing resolution
Measurement method:Inject fixed-amplitude pulses at known timeUse simple measurement to determine timing (threshold + interpolation)Significant structure seen
Delay lines also dependent onnoise on bias voltage, temperature
Very difficult to recover (requiresdetailed knowledge of noise spectrum)Evidence is seen of bias voltage noiseEvidence seen of temperature driftas well
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Feedback Loops
FPGA firmware contains several feedback loops to keep timing, voltages stable
Evidence seen that sampling rate varies slightly at both smaller and larger scalesFeedback loops in FPGA cannot compensate for small drifts
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Outside the ASIC
Channel-by-channel variation in t0 of up to several ns seen
Clock lines shared by 4 ASICs (across 4 boards)
Traces currently unterminated, may be causing distribution of start times
Each time FPGA design goes through place-and-route, different delays get set for different signals
Laser tests show ~2.1% crosstalk effect in MCP-PMT
Currently removed by ADC cut, but investigation into separation by both ADC and time underway
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Current Status of Calibrations
Voltage: pedestal correction onlyKurtis Nishimura working on proper gain correction
Timing:Large-scale t0 correctionsSample-by-sample timing corrections
Complete this list!
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iTOP Analysis Framework (topcaf)
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Pulser Data
There are two sample buffers with a depth of 64 samples
These need to be corrected for each ASIC (8 channels/ASIC)ASIC correction, so only one channel per ASIC was pulsed
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Image Plots
Mapping of x-y positioning to global channel number
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Pulser Raw Image
ASIC correction, so one channel per ASIC was pulsed1 problematic SCROD during these runs (4 ASICs were affected)
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Pulser Sample to Sample Corrections
There are two sample buffers with a depth of 64 samplesThese need to be corrected for each ASIC (8 channels/ASIC)
‘Even’ buffer ‘Odd’ buffer
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Pulser Sample to Sample Corrections
Before correction, two obvious peaks appearAfter correction, single peak seen
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Pulser Resolution
One entry per ASIC in histogram (64 total)4 ASICs with > 100 ns timing
still investigating, but all row 0 col 2 ASICs – may be FPGA issue
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Pulser Corrected Image
Corrected image much cleaner, aligned properly
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Laser Data
At LEPS, laser injected into bar via fiber at far cornerResulted in very uneven coverage
Left/right differences, hot spot, and almost no photons in lower PMTsDifference in arrival times at PMTs across the bar
4cm = ~193cm in quartz
2.54 m
0.45 m
2.58 m
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Laser Image with Pulser Corrections
Additional timing offsets from laser trigger delays and PMT/PMT wiring offsets
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Laser Resolution
Laser resolution after pulser corrections worse than pulser resolution (~140 ps vs. ~70 ps)
Pulser Laser
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Laser Resolution (time walk)
Additional calibration of time walk due to varying amplitude requiredCurrently just ad-hoc correctionlatest???
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Laser Resolution (time walk)
Ad-hoc correction recovers pulser timing in laser data (~90 ps)
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Final Laser Image
Clear image of laser wavefront reflectingMore data processing needed to measure resolutionsInvestigating methods of recovering lower PMTs (256+)
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Beam Image (cos θ = 0, x=0)
Using ADC range cut Need proper gain calibration
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Beam Image (cos θ = 0.39, x=-1.0 cm)
ADC range cut , need proper adc amplitude calibration work is ongoing
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Beam Image (cos θ = 0.37, x=20.0 cm)
ADC range cut , need proper adc amplitude calibration work is ongoing
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More on framework?
MC details?Versions? Backgrounds?