nato workshop – yalta, may 18 th 2005 front-end electronics for radiation sensors: basic...

NATO workshop – Yalta, May 18th 2005

Front-end electronics for radiation sensors: basic principles and applications to

homeland securityAngelo Rivetti – INFN Sezione di Torino


Outline

Integrated multi-channel front-end architecture analogue readout binary readout mixed-mode readout technological considerations

Application to security problems The context Some solutions: a very incomplete overview Conclusive remarks


Analogue readout (1)

FE

T&H

MU

XM

UX

ADCADC

Digital logicDigital logic

T&H

T&H

FE

FE

Trigger, clk, ctrl

FE

T&H

MU

XM

UX

ADCADC

Digital logicDigital logic

T&H

T&H

FE

FE

Trigger, clk, ctrl

+ Low amount of data+ Low power+ Preserve analogue information (only the peak of the signal is sensed)- Transmission of analogue signals to the external ADC.

Trigger driven event data selection

FE=preamplifier+shaper


After Ref [1], [2].

Design example: self triggered sampling

+

-

Vdd

Vin

CH

FE

+

-

Vdd

Vin

CH

FE


Two phase PDH

Concept developed at Brookhaven and based on a novel peak detector designed by the BNL instrumentation division (G. De Geronimo et al.). Two-phase scheme to optimize accuracy and driving capability.

+

-

Vout

Vos

Vdd

+

-

Vos

Vdd

Vin

Write phase Read phase

CH CH


Peak detection and derandomization

PD1PD1

PD2PD2

PDNPDN

Control logicControl logic

Vin Vout

Event driven event data selection


Peak detection and derandomization (2)

PD1PD1

PD2PD2

PDNPDN


Vin Vout

PD1PD1

PD2PD2

PDNPDN


Vin Vout

“Brute force” approach Alternative approaches


Peak detector features

Self triggered system: ideal for spectroscopy application Low power consumption Derandomization: ADC sampling rate can be tuned on the average event rate Data concentration: only the interested pulses are read-out, while baseline samples are disregarded. Technology: 0.35 m CMOS @ 3.3 V. Cell area: 340 x 50 m2 (analogue) + 245 x 50 m2 (digital) Absolute accuracy: 0.2 % for 2.7 Volt input range and 500 ns shaping time


Application example

Spectrum of 241Am taken with a system using the PDH circuit (After [2]).


Mixed-mode readout

Strictly speaking most front-end ICs incorporate some digital functions and are mixed-mode design. We focus here on “digitizing” front-ends. The analogue information is preserved and the information is digitized on board of the ASIC. The key advantage is that only more robust digitized data must be sent out of the chip. In most applications in high-energy and nuclear physics the signal need to be captured only at specific time instants. An analogue memory is used to sample rapidly changing signals with low power consumption. A slower ADC converts only pre-selected samples.


Sampling channel.

C0 C1 CN

BufferFE

Compact and fast sampling. Up to 512 sampling cells/channel have been implemented [3]. Several architectures are possible Voltage-write Voltage-read approach minimizes capacitance non-idealities.


The simplest ADC

Simple and suitable for massive parallelism. Low power consumption. Slow (Tconv = 2N Tclock). Most common approach in HEP ASICs, but other architectures (SAR, pipeline, etc.) have also been used.

Counter

LatchB0B1BN-1

analogue voltage ramp

Vin

Clk, ctrl

Digitized data


A mixed-mode readout example (1)

S. Kleinfelder, “Gigahertz Waveform Sampling and Digitization Circuit Design and Implementation”, IEEE Transaction on Nuclear Science, Vol. 50, No. 4, August 2003.

Circuit performance (ATWD chip):

4 channels with 128 sampling cells/channel Sampling frequency from 50 kHz to 2 GHz. Input bandwidth: 350 MHz. Noise: 1mV rms. Signal to noise ratio: 3000 : 1. 10 bit on chip digitization. No fast external control signals. 128 Wilkinson-type ADCs. Power consumption: 37 mW/channel @ full speed. Technology: 1.2 m CMOS!



Defines the sampling interval

Sampling instant is defined by a pulse, delayed by a complex delay-line with adjustable delay.

After sampling, all the 128 samples in one channel are digitized simultaneously by the 128 Wilkinson-type ADC.

The comparator and the latches are individual, the counter and ramp generator are shared among all the converters.

Counter

LatchB0B1BN-1


Vin

Clk, ctrl

Digitized data

Counter

LatchB0B1BN-1


Vin

Clk, ctrl

Digitized data



Simplified schematic (left) and example of of signal captured and digitized by the chip (top; time scale is 10 ns/div). (After [3]).Total dead time: < 100 s, most due to datatransmission.


Binary readout

Early and simplest for of A/D conversion. Information on amplitude is lost. Heavy information suppression: less data but system can be more difficult to debug. Very often requires threshold adjustment on a channel by channel basis

Digital pipelineFE

VTH

Digital pipelineFE

VTH

Digital pipelineFE

VTH

Digital pipelineFE

VTH


Analogue readout in the ALICE ITS

HAL25 Active shaper

Average power consumption:360 W/ch @ 1.4 s and 2.5Power supply (After[6]).


Mixed-mode readout in the ALICE ITS

The ASICs incorporates all the biasing circuitry on board and works with 4SMD capacitors of 100 nF


Binary readout in the ALICE ITS

Scheme of an individual pixel (after [6]). Front-end detail(after [7]


What next?

In the recent past deep submicron CMOS technologies became very popular in the design of front-end ASICs for particle detectors.

Quarter micron processes offer very good compromise between performance, cost and “simplicity” of use.

Quarter micron processes are very mature (obsolete?!), 0.13 m in full production, 0.09 m not very far away…

Scaling is driven by need of improving the performance of digital circuits (most of the markets).

Not too much consideration for the need of analogue designers

No consideration at all for the need of HEP (we are irrelevant costumers!)


Scaling....

After P. Fisher, “Readout of Pixel detectors : some thoughts on the next chipGeneration”, presented at Vertex 2001.

However, scaling can be very beneficial also to our applications!


Scaling and analogue

Some properties of the transistors which are important for analogue design tend to improve with scaling the technology (but not the transistor itself!).

Gate oxide thickness is reduced, also the power supply is.

If the power budget in my front-end channel is constant, I can use more current to get the same (or better performance), but…

Power dissipation in cable is increased!!

Cooling will be even more an issue.


A closer look

Power dissipation in class A amplifier

currvolpolddpol

LpolL

pol

in

in

SNRkTfPwr

ff

ftfdt

d

ft

IVI

CVIVCI

VVVV

118

2,2

2cos2

2sin

00

0

0


A closer look

For the same power, analogue performance may decrease due to the reduced supply voltages. Cost will increase by a big amount (4x form 0.25 to 0.13 generation:600k$ for a typical set of mask!) Complexity of the technology will increase (huge design rule manuals!), with increase in design time. New phenomena will come into play (nonlinear output conductance, gate current…) Front-end designs (massive parallelism, i.e. repetition of the same structures along the chip) can be prone to yield problem. Stick strictly to the recommended rules! Enlarge design groups to master the complexity of the designs and maximize the potential of the technology.

From detector specific ASICs to reconfigurable chips


Applications to security issues: a front-end designer point of view!

Disclaimer…


Applications to security issues: the context

The September 11th facts have boosted the emphasis on the improvement of existing techniques or developments of new ones that can help in preventing terrorist strikes.

Nuclear Science provides key competences and techniques in two major areas:

1. Detection of conventional explosives and weapon.2. Identification of radiological and nuclear threats.

The body of knowledge developed by the nuclear and high energy physics basic research community can be exploited in a two-fold way:

1. Exporting and adapting techniques already developed for basic research purposes.

2. Exporting the competence to devise new solutions.


Characteristics of detectors for security

Passive and active methods.

Size ranging from handy to containers.

Distance between the inspected object from contact to 50 – 100 m.

Very low-noise to maximize sensitivity and reduce false positives.

Low-cost and easy to operate.


Detecting conventional explosives

The goal is to find dangerous substances that might be hidden in small quantity in luggage or in higher quantity in maritime containers.

The inspection time has to be short (seconds to minutes).

The substance is identified by a quantitative analysis (which elements and in which proportions).

Element to be identified: nitrogen, oxygen, carbon, hydrogen.

Need of penetrating probes:

1. Neutron based systems.

2. Gamma ray based systems.

3. Others.


Detecting nuclear material

Finding significant amount of fissile material.

Note: some fissile material, like 235U is difficult to detect due to its low activity!

Identifying elements used in civil applications (e.g. radioisotopes used for medical applications) that might be exploited for “dirty” bombs.

Emphasis is on gamma ray and neutron detectors


Gamma ray detectors

Comparative table ofGamma ray detectors(After[7]).


Application example (1a)

[9] Rahmat Aryaeinejad and David F. Spencer: “Pocket Dual Neutron/Gamma Radiation Detector”, IEEE Transactions on Nuclear Science, vol. 51, no. 4, August 2004, pp. 1667-1671.

Portable system capable of simultaneous detection of neutron and gamma ray. Sensor: combination of 6Li and 7Li. Detector: PM tube with front-end electronics based on commercial components. Analogue signal processing + control and data manipulation via a microcontroller. Operated via a Li-ion battery. Size: 1.5 x 3.5 x 4 inch.


Application example (1b)

System layout (after[9]).


Application example (1c)

Performance example with a Cf-252 source (after [9])


Application example (2a)

T. O. Tümer et al. “Preliminary Results Obtained from a Novel CdZnTe Pad Detector and Readout ASIC Developed for an Automatic Baggage Inspection System”, presented at the 2000 IEEE NSS-MIC Symposium, Lyon, France.

Sensor: linear pad detector array. Pad size: 1 mm2

Sensor material: CdZnTe. Detection: x-ray in the 20 keV – 200 keV range. Readout: custom designed front-end chip (FESA).


Application example (2b)

[11] M. Clajus et al., “Front-End Electronics for Spectroscopy Applications (FESA) IC”, presented at the 2000 IEEE NSS – MIC Symposium, Lyon, France, October 2000.

Integrated circuit with 32 channels. Each channel:

preamplifier + two-stage variable gain amplifier. 5 comparators and counters to allow coarse pulse height analysis.

Gain and baseline adjustable channel by channel. Thresholds common to all channels. Counting rate > 1M counts/sec. Chip size: 7.3 x 10.0 mm2.


Application example (2c)

CSA VGA

VTH5

VTH4

VTH3

VTH2

VTH1

CSA VGA

VTH5

VTH4

VTH3

VTH2

VTH1

Counter

Counter

Counter

Counter

Counter

Readout


Other ideas

Active techniques need a probe that should: easily penetrate thick materials be readily available not too expensive not too dangerous…

Muon: who ordered that??

Mu-Vision [11]: funded by scientists and businessmen to develop commercialdetection systems based on probing materials with cosmic rays muons

Basic idea: to exploit multiple scattering (the nightmare of HEP and nuclearphysicists and of their engineers counterpart…) to identify hazardous materials (e.g. fissile material hidden in cargo).A lot of work being done at the Los Alamos National Lab [10].


Proposed cargo inspection system


Concluding remarks

Very complex and high-performance integrated circuits for the readout of particle detector have been designed by the nuclear and high-energy physics community

The big effort of the LHC electronics development came in a “gold era”: leading market process was very suitable to the application and not too expensive.

This picture is going to change in the future: more complex and expensive technologies, but we have to live with that!

The solution: more cooperative effort to share design resources and costs and a slightly different approach (more flexible and re-usable chips)

With the right attitude, more powerful system can be designed exploiting very advanced CMOS technologies


Concluding remarks

As a critical components in nuclear instrumentation, front-end electronics finds application to other domain, including security.

The use of highly integrated front-end electronics improves several system aspects and reduces cost.

The designers coming from the basic research environment have the right knowledge (and may be also the right ASIC!)

Issue to address: lack in communication between different communities and shortage of designer time (often “absorbed” also in other aspects of the system)


References

[1] G. De Geronimo, A. Kandasamy, and P. O’ Connor, “Analog CMOS peak detect and hold circuit – Part 2: Offset-free and rail-to-rail derandomizing configuration”, Nucl. Instrum. Methods.[2] G. De Geronimo, A. Kandasamy, and P. O’ Connor, “Analog Peak Detector and Derandomizer for High-Rate Spectroscopy”, IEEE Trans. Nucl. Science, vol. 49, no. 50, August 2002, pp. 1769 – 1773.[3] S. Kleinfelder, “Gigahertz Waveform Sampling and Digitization Circuit Design and Implementation”, IEEE Trans. Nucl. Science, vol. 50, no. 4, August 2004, pp. 955 – 962. [4] J. Kaplon, et al. “Fast CMOS Transimpedance Amplifier and Comparator Circuit for readout of silicon strip detectors at LHC experiments”, Proceedings of the 8th workshop on electronics for LHC experiments, Colmar, France, 2002.[5] C. Hu et al., “The HAL25 front-end chip for the ALICE silicon strip detectors”,Proceedings of the 6th workshop for the electronics for the LHC experiments, Krakow, Poland, September 2000.[6] K. Wyllie et al., “A pixel chip for tracking in ALICE and particle identification in LHCb”, presentation given at the FEE2000 meeting, Perugia, May 2000.[7] R. Dinapoli, “An analog front-end in standard 0.25 mm CMOS for silicon pixel detector in ALICE and LHCb”, Proceedings of the 6th workshop for the electronics for the LHC experiments, Krakow, Poland, September 2000.[8] DOE Report (DOE/SC-0062).[9] R. Aryaeinejad and D. F. Spencer: “Pocket Dual Neutron/Gamma Radiation Detector”, IEEE Transactions on Nuclear Science, vol. 51, no. 4, August 2004, pp. 1667-1671[10] L. J. Shultz et al., “Image reconstruction and material Z discrimination via cosmic ray muon radiography”, NIM – A 509, 2004, pp. 687-694.[11] www.muonvision.com

nato workshop – yalta, may 18 th 2005 front-end electronics for radiation sensors: basic...

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nato workshop yalta

time slide

torino slide

phase ch slide

self triggered sampling

analogue information

data low power

preamplifier shaper