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## (MINOS NearDet) Electronics Overview

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Introduction

- Basics of signal measurement
- Photons
- PMT Signals
- ADCs
- MINOS Near Detector Electronics
- Front End vs. Readout
- Run Types
- Data Format

Peter Shanahan – Fermilab

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

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!

t

I(t)

Anode Signal

t

PMT Signals(Last) Dynode signal: smaller image of anode signal

Peter Shanahan – Fermilab

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

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

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

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

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

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

Pedestal

- Ideal case: no input, constant output
- Mean ADC count for no inputpedestal
- 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

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

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

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

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

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

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

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

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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