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iTOP LEPS Beam Test Analysis
LYNN WOOD
JULY 17, 2013
PACIFIC NORTHWEST NATIONAL LABORATORY
Topics
LEPS Beam Test Summary
iTOP Electronics OverviewIRS3B ASIC
CorrectionsVoltage
Timing
Current Analysistopcaf (software)
Results
Next Steps
LEPS Beam Test – June 4-20, 2013
Goal: end-to-end test withFull quartz bar including mirror and prism
Full bar of PMTs and ASIC-based electronics
Belle 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 electrons
Photons strike Pb target, produce e+/e- pairs that pass through detector
LEPS Configuration
e+ beam trigger from four counters g rate: 30 kHz
Trigger rate: 10 Hz
DAQ 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 = 0cm
Cos q = 0.37, x = 20cm
iTOP Electronics Overview
Physical Layout
One SCROD
One ASIC
One carrier board
ASIC Block Diagram
Per channel:Single input
128 sampling cells (capacitors)
256 transfer cells
32768 storage cells
64 counters for digitization
Per ASIC:Timing generator
Ramp generator (for digitization)
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 response
Input coupling and signal frequency content
Timing uncertaintiesOverconstrained timing – overlap/gap between records
Varying delays from sample-to-sample
Bias voltage (and noise on bias voltage), temperature drift
Feedbacks cannot currently compensate for small drifts
Outside the ASIC:Clock shared in “columns” across boards – currently unterminated traces
Path length differences in FPGA for different ASICs
Crosstalk between channels
Comparator Response
ADCs are Wilkinson-style ramp comparators
Fires when ramp exceeds stored voltage
Signals stored with DC offset to fit into ADC’s dynamic range
Offset varies cell-to-cell = pedestal correction
Comparator response is nonlinear
Transfer function varies for each storage cell
Examples here from IRS2 and TARGET5 ASICs (same comparator as IRS3B)
AC vs. DC response
Transfer functions measured with DC inputs, but AC response may be different
One example: persistenceVoltage has some dependence on previous-stored voltage
Will show “ghost” pulse for 1+ cycles
Will also reduce pulse height
Should primarily affect large pulses
Example from PSEC3 chip at right
Input Coupling
Multiple components:Amplifier bandwidth
Coupling into ASIC sample cellsCan 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 same
Hard to measure gain without fixed-height samples
Need calibration signals that look like MCP-PMT signals!
Laser Pulser
Overconstrained Timing
Timing within each 128 samples controlled by delay lineTiming controlled by bias on delay line
Each 128 sample set started with input clock
Incorrect biasing may end sample too soon (gap between samples) or too late (overlap between samples)
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 time
Use 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 noise
Evidence seen of temperature driftas well
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 scales
Feedback loops in FPGA cannot compensate for small drifts
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
Current Status of Calibrations
Voltage: pedestal correction onlyKurtis Nishimura working on proper gain correction
Timing:Large-scale t0 corrections
Sample-by-sample timing corrections
Complete this list!
iTOP Analysis Framework (topcaf)
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
Image Plots
Mapping of x-y positioning to global channel number
Pulser Raw Image
ASIC correction, so one channel per ASIC was pulsed1 problematic SCROD during these runs (4 ASICs were affected)
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
Pulser Sample to Sample Corrections
Before correction, two obvious peaks appear
After correction, single peak seen
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
Pulser Corrected Image
Corrected image much cleaner, aligned properly
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 PMTs
Difference in arrival times at PMTs across the bar4cm = ~193cm in quartz
2.54 m
0.45 m
2.58 m
Laser Image with Pulser Corrections
Additional timing offsets from laser trigger delays and PMT/PMT wiring offsets
Laser Resolution
Laser resolution after pulser corrections worse than pulser resolution (~140 ps vs. ~70 ps)
Pulser Laser
Laser Resolution (time walk)
Additional calibration of time walk due to varying amplitude requiredCurrently just ad-hoc correction
latest???
Laser Resolution (time walk)
Ad-hoc correction recovers pulser timing in laser data (~90 ps)
Final Laser Image
Clear image of laser wavefront reflectingMore data processing needed to measure resolutions
Investigating methods of recovering lower PMTs (256+)
Beam Image (cos θ = 0, x=0)
Using ADC range cut Need proper gain calibration
Beam Image (cos θ = 0.39, x=-1.0 cm)
ADC range cut , need proper adc amplitude calibration work is ongoing
Beam Image (cos θ = 0.37, x=20.0 cm)
ADC range cut , need proper adc amplitude calibration work is ongoing
More on framework?
MC details?Versions? Backgrounds?