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Peter Shanahan – Fermilab1 (MINOS NearDet) Electronics Overview A heuristic, pedagogical introduction.

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Presentation on theme: "Peter Shanahan – Fermilab1 (MINOS NearDet) Electronics Overview A heuristic, pedagogical introduction."— Presentation transcript:

1 Peter Shanahan – Fermilab1 (MINOS NearDet) Electronics Overview A heuristic, pedagogical introduction

2 Peter Shanahan – Fermilab2 Introduction Basics of signal measurement –Photons –PMT Signals –ADCs MINOS Near Detector Electronics –Front End vs. Readout Run Types Data Format

3 Peter Shanahan – Fermilab3 Prologue Photons: Wavelength Shifting Fiber Module Connector Alner Box PMT (M64) Scintillator Strip Ionizing particle Plane Commissioning Shifts Clear Fiber Typical muon in MINOS leads to roughly 20-40 photons reaching the PMT.

4 Peter Shanahan – Fermilab4 Photo-Multiplier Tube Each photon has a ~20% (Quantum Efficiency) chance of liberating 1 electron from the photo-cathode: photo-electron. Photo-Cathode 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. Photon -HV WARNING: CHEESY SCHEMATIC!

5 Peter Shanahan – Fermilab5 PMT Signals I(t) t Anode Signal I(t) t (Last) Dynode signal: smaller image of anode signal

6 Peter Shanahan – Fermilab6 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: 1x10 6 160fC anode signal per photo-electron 1 PE signal

7 Peter Shanahan – Fermilab7 Photostatistics Poisson statistics at Cathode –Creation of each PE is random process –Number of PEs 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

8 Peter Shanahan – Fermilab8 Electronics Requirements Sensitivity to single PE signal Ability to measure signals up to 100+ PEs Ability to resolve interactions occurring within ~100 ns in same channel

9 Peter Shanahan – Fermilab9 What to Measure? Probability of Photon on Cathode/Unit time Time WLS fiber excitation has ~10ns decay constant In any time window, PEs are poisson distributed I(t) or V(t) Time Instantaneous peak voltage (current) is useless as measure of PEs! I(t) or V(t) Two examples with same total PEs

10 Peter Shanahan – Fermilab10 Charge Measurement I(t) Integrate Charge onto Capacitor over some time C Measure Voltage (= Q/C) with Flash-ADC (analog-to-digital converter) Flash ADC Series of Comparators tied to voltage ladder – e.g., 255 comparators over 0-2V Last comparator with Vin>Vref turned into digitized code (8 bits in MINOS ND case)

11 Peter Shanahan – Fermilab11 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

12 Peter Shanahan – Fermilab12 Pedestal Ideal case: no input, constant output –Mean ADC count for no input pedestal Real case: electrical noise smears any input 0 0 Pedestal value (ADC Counts) If pedestal is too low, you lose some information below ADC floor

13 Peter Shanahan – Fermilab13 Dynamic Range We need sensitivity to very small ( 10pC) signals. One way to achieve dynamic range: enough bits, and 2 enough comparators in a flash-ADC Or, multi-ranging device CCC I/2 I/4 I/8 … I/256 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

14 Peter Shanahan – Fermilab14 MINOS MENU Card Basic Channel unit of MINOS ND Electronics QIEFADCFIFO Input current Analog Voltage 8-bit FADC value 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 Input charge QIE output voltage

15 Peter Shanahan – Fermilab15 System Overview Front End (MINDER/MENUS) Readout (MASTER) Data Acquisition Analogue PMT Pulse Fast readout of digital data in response to trigger PVIC Transfers to PCs Timing System 44 MINDER crates 8 MASTER crates

16 Peter Shanahan – Fermilab16 Front-End Crates MINDER Cards (up to 16 per crate) Up to 4 per PMT (so 4 PMTs per crate)... KEEPER Card Controls triggering of data writing into local buffers, And other functions MINDER Timing Module (MTM) Provides timing signals to each MINDER, KEEPER PMT Dynode signal inputs Readout by Dynode 0 MINDER Cards: 16 MENUs each 0 1 2 3

17 Peter Shanahan – Fermilab17 MINDER Cards Cable Bundle from PMT MINDER Card Home to 16 MENU Cards Data to MASTER Crate Backplane MINDER Auxiliary Card MENU Cards: Store data locally until readout 8 RF buckets for Dynode triggers ~520 RF buckets for Spill mode

18 Peter Shanahan – Fermilab18 MASTER Crates Each MASTER has 8 input channels – 1 per MINDER RIO VME Processor Controls data transfers in crate, and controls KEEPER cards in MINDER crates VTM: VME Timing Module Distributes timing signals within crate Up to 12 MASTERs per Crate

19 Peter Shanahan – Fermilab19 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.

20 Peter Shanahan – Fermilab20 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 10 s beam spill Dynode trigger –1/3 of mean PE for each PMT = NullTrigger

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