Yamagaya Shohei Study about behavior of a prototype ASIC for the upgraded ATLAS pixel detectors with low thresholds Year-End-Meeting 2019/12/23 Shohei Yamagaya (Osaka univ.)
Introduction 2 ATLAS pixel detector will be upgraded for HL-LHC. New Pixel Detector • Total Size : 4cm × 4cm • Pixel Size : 50um × 50um • 4 ASICs with 1.28 Gbps readout • Prototype ASIC for the new pixel detector • Name : RD53A • Can judge if there is a hit or not • Can estimate amount of input charge • It has registers to configure its circuits. Year-End-Meeting Yamagaya Shohei 2019/12/23
ASIC 3 1 pixel of the sensor Register Front-End Global Pixel Circuit • Comparator with threshold • ADC (Time over Threshold) Threshold voltage HitMap, ADC value A threshold voltage is set by ASIC’s register values. • We have to tune them to set the threshold as we aim for. • All pixels should have similar thresholds after tuning. Year-End-Meeting Yamagaya Shohei 2019/12/23
Threshold tuning 4 Flow chart of tuning After global tuning Threshold_Distribution Threshold_Distribution # pixels hist # pixel 1000 Entries 380 Mean 1822 32.97 ± Change Global Reg Std Dev 359.2 Underflow 0 800 Overflow 333 Integral 2.277e+04 600 No 400 measure threshold 200 Similar to target? 0 0 500 1000 1500 2000 2500 3000 Threshold[e] YES Measured threshold [e] After pixel by pixel tuning ThresholdDist target:1720 ThresholdDist target:1720 Change Pixel Reg # pixels Threshold_1d Threshold_1d_copy 10000 # pixels Entries Entries 26112 26112 9000 Mean Mean 1767 1767 0.3786 0.3786 ± ± Std Dev Std Dev 61.17 61.17 8000 Underflow Underflow 0 0 No Overflow Overflow 6 6 7000 Integral Integral 2.611e+04 2.611e+04 measure threshold 6000 Pixel individuality 5000 Similar to target? 4000 3000 YES 2000 1000 Finish 0 500 1000 1500 2000 2500 3000 Threshold Measured threshold [e] Year-End-Meeting Yamagaya Shohei 2019/12/23
Requirement for ASIC 5 • One of the requirements for the new ATLAS detector • Untuned pixels < 0.3% of all && threshold dispersion < 40[e] target_threshold : 900 target_threshold : 900 tmp_thre tmp_thre # pixels # pixels 26112 26112 Entries Entries 4 10 947.1 966.3 0.2076 0.203 Mean Mean ± ± 33.54 32.8 Std Dev Std Dev Underflow Underflow 0 0 0 0 Overflow Overflow 3 10 Untuned pixels Integral Integral 2.611e+04 2.611e+04 Definition of untuned pixels 2 10 • Measured threshold =0 10 • |Measured threshold - target one| > 3 σ 1 0 500 1000 1500 2000 2500 3000 threshold[e] Measured Threshold Measured threshold =0 No one studied tuning and threshold behavior even though it has the requirement to fulfill Year-End-Meeting Yamagaya Shohei 2019/12/23
Setup 6 • YARR : a project for rapid readout from ASIC (developed by LBNL) • It has an algorithms to tune each pixel’s threshold. • It will be also used for QA/QC test in mass-production. • Untuned pixels were counted for each target threshold. • Target threshold’s range : 0 ~ 2000 [e] because pixel detector’s threshold will be 600 ~ 800[e]. Setup Adapter card PCIe Display YARR-SW Port FPGA board ASIC (FW : YARR-fw) Year-End-Meeting Yamagaya Shohei 2019/12/23
Untuned pixels 7 • Case : a threshold is different from target • That pixel’s individuality is too large for pixel register to tune it. • Too low -> pixel register (5bit) = maximum(15) • Too high -> pixel register = minimum(-15) • other Pixel Register’s value Dist. TDACDist target:1700 TDACDist target:1700 scan failed #pixels # pixels no response • Blue : Too high or Too low 4 out_saturated 10 • Other out_notsaturated 3 10 • Measured threshold = 0 2 10 10 1 15 10 5 0 5 10 15 20 − − − TDAC Pixel Register’s value Year-End-Meeting Yamagaya Shohei 2019/12/23
Untuned pixels 8 • Measured Threshold = 0 ： divided into 2 types • The threshold measurement was failed. • Non responsive pixels After global tuning Initial state Noise floor Threshold Pixels below noise floor output nothing. Algorithm can’t tune such pixels to target threshold Non responsive pixels are predicted to increase with low target threshold. Year-End-Meeting Yamagaya Shohei 2019/12/23
Threshold behavior 9 Threshold_vs_target Threshold_vs_target Measured Threshold [e] 3000 10000 Threshold[e] 9000 2500 8000 7000 2000 6000 Threshold mean 1500 5000 4000 1000 • Target threshold > 200 [e] 3000 mean-target threshold 2000 500 • | measured - target | < 10[e] 1000 0 0 • Threshold tuning is succeed 0 200 400 600 800 1000 1200 1400 1600 1800 2000 Measured - target [e] target_threshold[e] 20 10 0 − 10 20 − 0 200 400 600 800 1000 1200 1400 1600 1800 2000 target_threshold Target Threshold [e] Year-End-Meeting Yamagaya Shohei 2019/12/23
Ratio of untuned 10 Color rule ▶︎ • Threshold 3 σ away from mean • Too high Ratio of the untuned pixels • Too low LowerLimit0 LowerLimit0 scan failed Ratio of untuned pixels • Pixel Reg is not saturated no response # pixels 1 out_TDAC=15 • Non-responsive pixels out_TDAC=-15 • configuration’s problem out_notsaturated − 1 10 Requirement for 2 − 10 pixel detector untuned pixels < 0.3% 3 − 10 − 4 10 0 200 400 600 800 1000 1200 1400 1600 1800 2000 target_threshold Target threshold [e] The requirement is satisfied! (400 < target threshold < 800[e]). Year-End-Meeting Yamagaya Shohei 2019/12/23
Conclusion 11 • The ASIC for the new ATLAS pixel detector was tested about a threshold tuning of each pixel. • We found the ASIC satisfy the requirement for it. • The increase of non responsive pixels with low threshold was revealed for the first time. And, they are dominant with a target threshold below 400 [e]. • This result will be a good benchmark for QA/QC tests in mass- production of the prototype ASIC and revised one. Year-End-Meeting Yamagaya Shohei 2019/12/23
Back Up
Threshold scan 13 • YARR’s scan consists of the 4 functions. How to measure thresholds Scurve-320-96-403.169325 50 Number of hits 40 Threshold 30 Occupancy 50% 20 10 0 0 20 40 60 80 100 Injection charge Vcal • Tuning : a scan + change global/pixel register’s value Year-End-Meeting Yamagaya Shohei 2019/12/23
Avoid “ non responsive " 14 • Before the tuning to target, the one to 800[e] was done. -> This process can reduce non-responsive pixels Threshold Pixels with a threshold below noise floor are decreased! Threshold Noise floor Year-End-Meeting Yamagaya Shohei 2019/12/23
Avoid “ non responsive ” 15 no response no response Ratio of “non responsive pixels” no response no response Ratio of untuned pixels # pixels # pixels 1 1 1 − 1 − 10 10 normal tuning 2 − 2 − 10 10 3 − − 3 10 10 4 − 4 10 − 10 Tuned initial state 0 200 400 600 800 1000 1200 1400 1600 1800 2000 0 200 400 600 800 1000 1200 1400 1600 1800 2000 Target threshold [e] target threshold target threshold Year-End-Meeting Yamagaya Shohei 2019/12/23
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