IEEE NPSS Short Course

Radiation Detection and MeasurementOctober 19, 2008

2008 Nuclear Science Symposium and Medical Imaging ConferenceDresden, Germany

Front-End Electronics Systems forParticle Detection and Imaging

These course notes and additional tutorials athttp://www-physics.lbl.gov/~spieler

More detailed discussions inH. Spieler: Semiconductor Detector Systems, Oxford University Press, 2005

Front-End Electronics Systems for Particle Detection and Imaging – Introduction Helmuth Spieler2008 IEEE Nuclear Science Symposium LBNL

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Course Contents

1. Introduction

2. Signal AcquisitionDetector pulsesVoltage vs. Current Mode AmplifiersCharge-Sensitive AmplifierFrequency and Time Response

3. Resolution and Electronic NoiseThermal NoiseShot NoiseLow Frequency (“1/f ”) NoiseSignal-to-Noise Ratio vs. DetectorCapacitance

4. Pulse ProcessingRequirementsShaper ExamplesPulse Shaping and Signal-to-Noise Ratio

5. Some Other Aspects of Pulse ShapingBaseline RestorationPole-Zero CancellationBipolar vs. Unipolar Shaping

6. Timing MeasurementsTime JitterTime WalkCoincidence Systems

7. Digital Signal ProcessingSampling RequirementsDigital FilteringDigital vs. Analog

8. Systems and CircuitsApplications in HEP, Nuclear Physics,Materials Science, and Biology

9. Why Things Don’t Work

Front-End Electronics Systems for Particle Detection and Imaging – Introduction Helmuth Spieler2008 IEEE Nuclear Science Symposium LBNL

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Many different types of detectors are used for radiation detection.

Nearly all rely on electronics.

Although detectors appear to be very different, basic principles of the readoutapply to all.

• The sensor signal is a current.

• The integrated current ( )S SQ i t dt= ∫ yields the signal charge.

• The total charge is proportional to the absorbed energy.

Readout systems include the following functions:

• Signal acquisition

• Pulse shaping

• Digitization

• Data Readout

Front-End Electronics Systems for Particle Detection and Imaging – Introduction Helmuth Spieler2008 IEEE Nuclear Science Symposium LBNL

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Example: Scintillation Detector

number of photons number of photoelectrons charge in pulse∝ absorbed energy ∝ absorbed energy ∝ abs. energy

INCIDENTRADIATION

SCINTILLATOR PHOTOCATHODE ELECTRONMULTIPLIER

LIGHT ELECTRONS ELECTRICALSIGNAL

PHOTOMULTIPLIER

Front-End Electronics Systems for Particle Detection and Imaging – Introduction Helmuth Spieler2008 IEEE Nuclear Science Symposium LBNL

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Readout

charge in pulse pulse height∝ absorbed energy ∝ absorbed energy

PULSE SHAPING ANALOG TO DIGITALCONVERSION

DIGITALDATA BUS

Front-End Electronics Systems for Particle Detection and Imaging – Introduction Helmuth Spieler2008 IEEE Nuclear Science Symposium LBNL

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1. Basic Functions of Front-End Electronics

Pulse shaping can also be performed with digital circuitry:

INCIDENTRADIATION

SENSOR PREAMPLIFIER+ PRE-FILTER

PULSESHAPING

ANALOG TODIGITAL

CONVERSION

DIGITALDATA BUS

DIGITALSIGNAL

PROCESSOR

INCIDENTRADIATION

SENSOR INTEGRATINGPREAMPLIFIER

PULSESHAPING

ANALOG TODIGITAL

CONVERSION

DIGITALDATA BUS

Front-End Electronics Systems for Particle Detection and Imaging – Introduction Helmuth Spieler2008 IEEE Nuclear Science Symposium LBNL

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Many Different Implementations

“Traditional” Si detector system Tracking Detector Module (CDF SVX)for charged particle measurements 512 electronics channels on 50 µm pitch

Front-End Electronics Systems for Particle Detection and Imaging – Introduction Helmuth Spieler2008 IEEE Nuclear Science Symposium LBNL

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Spectroscopy systems highly optimized!By the late 1970s improvements were measured in %.

Separate system components:1. detector2. preamplifier3. amplifier

adjustable gainadjustable shaping

(unipolar + bipolar)adjustable pole-zero cancellationbaseline restorer

Beam times typ. few days with changing configurations, so equipment must bemodular and adaptable.

Today, systems with many channels are required in many fields.

In large systems power dissipation and size are critical, so systems are notnecessarily designed for optimum noise, but adequate noise, and circuitry istailored to specific detector requirements.

Front-End Electronics Systems for Particle Detection and Imaging – Introduction Helmuth Spieler2008 IEEE Nuclear Science Symposium LBNL

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Large-Scale Readout Systems

Example: Si strip detector

On-chip Circuits

Inside a typical readout IC: 128 parallel channels of analog front-end electronicsLogic circuitry to decode control signals, load DACs, etc.Digital circuitry for zero-suppression, readout

PREAMPLIFIER SHAPER ANALOG PIPELINE ADC

ANALOG SIGNAL PROCESSING

ANALOG SIGNAL PROCESSING

ANALOG SIGNAL PROCESSING

ANALOG SIGNAL PROCESSING

ANALOG SIGNAL PROCESSING

TEST PULSE GENERATOR, DACs, R/ W POINTERS, etc.

SPARSIFICATION

DIGITALCONTROLOUTPUTDRIVERS

TOKEN IN

CONTROL

DATA OUT

TOKEN OUT

Front-End Electronics Systems for Particle Detection and Imaging – Introduction Helmuth Spieler2008 IEEE Nuclear Science Symposium LBNL

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Readout of Multiple ICs

IC1 is designated as master.Readout is initiated by a trigger signal selecting appropriate time stamp to IC1.When all data from IC1 have been transferred, a token is passed to IC2.When IC3 has finished, the token is passed back to IC1, which can begin a new cycle.

CONTROL BUS

DATA BUS

TOKENPASSING

STRIP DETECTOR

IC3 IC2 IC1

Front-End Electronics Systems for Particle Detection and Imaging – Introduction Helmuth Spieler2008 IEEE Nuclear Science Symposium LBNL

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ATLAS Silicon Strip system (SCT): ABCD chips mounted on hybrid

Front-End Electronics Systems for Particle Detection and Imaging – Introduction Helmuth Spieler2008 IEEE Nuclear Science Symposium LBNL

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ATLAS SCT Detector Module

HYBRID ASSEMBLYBeO FACINGS

SLOTTED WASHER

SILICON SENSORS

BASEBOARD TPGDATUM WASHER

BeO FACINGSCONNECTOR

Front-End Electronics Systems for Particle Detection and Imaging – Introduction Helmuth Spieler2008 IEEE Nuclear Science Symposium LBNL

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Front-End Electronics Systems for Particle Detection and Imaging – Introduction Helmuth Spieler2008 IEEE Nuclear Science Symposium LBNL

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Cross Section of Module

READOUT ICs

BeO FACING (0.25)AIR GAP (0.4)

Cu-POLYIMIDE FLEXIBLE CIRCUIT (0.27)

SILICON SENSORS (0.285)

TPG HEAT SPREADER (0.38)WITH EPOXY COATING (0.02)

CARBON-CARBON BRIDGE (0.3)WITH PARYLENE COATING (0.01)

CONNECTORCOOLING BLOCK

10mm

1 mm

Front-End Electronics Systems for Particle Detection and Imaging – Introduction Helmuth Spieler2008 IEEE Nuclear Science Symposium LBNL

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Design criteria depend on application1. Energy resolution2. Rate capability3. Timing information4. Position sensing

Large-scale systems impose compromises1. Power consumption2. Scalability3. Straightforward setup + monitoring4. Cost

Technology choices1. Discrete components – low design cost

fix “on the fly”2. Full-custom ICs – high density, low power, but

better get it right!

Successful systems rely on many details that go well beyond “headline specs”!