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(MINOS NearDet) Electronics Overview

(MINOS NearDet) Electronics Overview. A heuristic, pedagogical introduction. Introduction. Basics of signal measurement Photons PMT Signals ADCs MINOS Near Detector Electronics Front End vs. Readout Run Types Data Format. Ionizing particle. Alner Box. Module Connector. PMT (M64).

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(MINOS NearDet) Electronics Overview

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  1. (MINOS NearDet) Electronics Overview A heuristic, pedagogical introduction Peter Shanahan – Fermilab

  2. Introduction • Basics of signal measurement • Photons • PMT Signals • ADCs • MINOS Near Detector Electronics • Front End vs. Readout • Run Types • Data Format Peter Shanahan – Fermilab

  3. Ionizing particle Alner Box Module Connector PMT (M64) Scintillator Strip Plane Commissioning Shifts Prologue • Photons: Wavelength Shifting Fiber Clear Fiber Typical muon in MINOS leads to roughly 20-40 photons reaching the PMT. Peter Shanahan – Fermilab

  4. Photo-Multiplier Tube Photo-Cathode Photon Each photon has a ~20% (Quantum Efficiency) chance of liberating 1 electron from the photo-cathode: photo-electron. -HV Electron accelerated to next dynode, liberates more electrons Anode: collection of total signal Gain: total number of electrons at anode, for 1 initial photo electron. Gain ~1 million in MINOS. Peter Shanahan – Fermilab WARNING: CHEESY SCHEMATIC!

  5. I(t) t I(t) Anode Signal t PMT Signals (Last) Dynode signal: smaller image of anode signal Peter Shanahan – Fermilab

  6. MINOS ND PMTs • M64 • Multi-anode PMTs. I.e., 64 input pixels, 64 output anode channels • Common dynode: use last stage to form readout trigger for entire PMT • 12 dynode stages • ~800 V total • Gain: 1x106 160fC anode signal per photo-electron • “1 PE” signal Peter Shanahan – Fermilab

  7. Photostatistics • Poisson statistics at Cathode • Creation of each PE is random process • Number of PE’s fluctuate around mean N with rms=sqrt(N). • Single PE smearing • Production of electrons at each dynode is also random • Poisson smearing  RMS ~25% beyond PE statistics e.g.: Poisson distribution with mean=6 Peter Shanahan – Fermilab

  8. Electronics Requirements • Sensitivity to single PE signal • Ability to measure signals up to 100+ PE’s • Ability to resolve interactions occurring within ~100 ns in same channel Peter Shanahan – Fermilab

  9. What to Measure? WLS fiber excitation has ~10ns decay constant Probability of Photon on Cathode/Unit time In any time window, PE’s are poisson distributed Time Instantaneous peak voltage (current) is useless as measure of PEs! I(t) or V(t) I(t) or V(t) Two examples with same total PEs Time Peter Shanahan – Fermilab

  10. Charge Measurement C I(t) Measure Voltage (= Q/C) with Flash-ADC (analog-to-digital converter) Integrate Charge onto Capacitor over some time Series of Comparators tied to voltage ladder – e.g., 255 comparators over 0-2V Flash ADC Last comparator with Vin>Vref turned into digitized code (8 bits in MINOS ND case) Peter Shanahan – Fermilab

  11. Analogue-to-Digital Converter • ADC • Key properties: Pedestal, Sensitivity, Dynamic Range, Noise, Linearity • Pedestal • What value the ADC gives for 0 input • Sensitivity • How much input change (charge or voltage) corresponds to a 1 unit change in output • Dynamic Range • The range of input signals over which the ADC is sensitive. • Noise • The variation in output for identical input Peter Shanahan – Fermilab

  12. Pedestal • Ideal case: no input, constant output • Mean ADC count for no inputpedestal • Real case: electrical noise smears any input 0 Pedestal value (ADC Counts) If pedestal is too low, you lose some information below ADC floor 0 Peter Shanahan – Fermilab

  13. C C C Dynamic Range • We need sensitivity to very small (<10fC) , and large (>10pC) signals. • One way to achieve dynamic range: enough bits, and 2enough comparators in a flash-ADC • Or, multi-ranging device I/2 • MINOS QIE: charge integrator and encoder: • Integrated Circuit divides input current simultaneously with different weights onto 8 different capacitor • Outputs 1 analogue voltage to a Flash ADC I/4 I/8 … I/256 Peter Shanahan – Fermilab

  14. MINOS MENU Card • Basic Channel unit of MINOS ND Electronics Input current 8-bit FADC value Analog Voltage QIE FADC FIFO 3 bit range code 2 bit CAP-ID code CAP-ID: QIE has 4 copies of current divider/integrator  4 capacitor IDs Every channel in the detector (9240) produces, every 18.87 nsec: {FADC, RANGE, CAP-ID} 1.4fC lowest count sensitivity, 16-bit effective dynamic range QIE output voltage Input charge Peter Shanahan – Fermilab

  15. System Overview Timing System 8 MASTER crates 44 MINDER crates Front End (MINDER/MENUS) Readout (MASTER) Data Acquisition Analogue PMT Pulse Fast readout of digital data in response to trigger PVIC Transfers to PCs Peter Shanahan – Fermilab

  16. Front-End Crates PMT Dynode signal inputs MINDER Cards (up to 16 per crate) Up to 4 per PMT (so 4 PMTs per crate) MINDER Timing Module (MTM) Provides timing signals to each MINDER, KEEPER 0 1 2 3 KEEPER Card Controls triggering of data writing into local buffers, And other functions . . . Readout by Dynode 0 MINDER Cards: 16 MENUs each Peter Shanahan – Fermilab

  17. MINDER Cards • MENU Cards: • Store data locally until readout • 8 RF buckets for Dynode triggers • ~520 RF buckets for Spill mode Cable Bundle from PMT MINDER Auxiliary Card Data to MASTER MINDER Card Home to 16 MENU Cards Crate Backplane Peter Shanahan – Fermilab

  18. MASTER Crates “RIO” VME Processor Controls data transfers in crate, and controls KEEPER cards in MINDER crates Each MASTER has 8 input channels – 1 per MINDER Up to 12 MASTERs per Crate VTM: VME Timing Module Distributes timing signals within crate Peter Shanahan – Fermilab

  19. MASTER Cards • Data input • Sucks in data from all triggered MINDERs • Linearization • Based on Charge Injection Calibration of MENUs, FADC, Range, CapID are turned into linearized 16-bit number = “a digit” • Lookup Table stores calibration for each channel: every possibly 16 bit input word (FADC, RANGE, CAPID) is an address in memory. Value stored at that address is the Calibrated Output. • Sparsification • Only digits > 20 calibrated counts (~1/6 PE) above pedestal are stored for readout • Storage • Data are stored in MINDER during 25(?) ms period until Buffer Swap, when data are read out by DAQ PCs. Peter Shanahan – Fermilab

  20. Run Types • VME Triggers • Collection of digits (calibrated or not) for a specified time • Used for Pedestal measurement (NearExpert), Charge Injection Calibration (NearCalibrate), and NearCalCheck runs. • Spill mode • Collect every digit for entire 10ms beam spill • Dynode trigger • 1/3 of mean PE for each PMT = NullTrigger Peter Shanahan – Fermilab

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