Outline

1. Front-end electronics for radiation sensors: basic principles and applications to homeland security Angelo Rivetti – INFN Sezione di Torino

2. 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

3. Analogue readout (1) FE=preamplifier+shaper Trigger driven event data selection + 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.

4. Design example: self triggered sampling After Ref [1], [2].

5. Vout Vdd Vdd Vin - - + + Vos Vos CH CH Read phase Write phase 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.

6. Peak detection and derandomization PD1 PD2 Vin Vout Event driven event data selection PDN Control logic

7. Peak detection and derandomization (2) “Brute force” approach Alternative approaches

8. 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 mm CMOS @ 3.3 V. • Cell area: 340 x 50 mm2 (analogue) + 245 x 50 mm2 (digital) • Absolute accuracy: 0.2 % for 2.7Volt input range and 500 ns shaping time

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

10. 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.

11. Sampling channel. Buffer FE C0 C1 CN • 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.

12. Vin Digitized data Latch BN-1 B1 B0 analogue voltage ramp Clk, ctrl Counter 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.

13. 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. • Inputbandwidth: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 mm CMOS!

14. A mixed-mode readout example (2) 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. Defines the sampling interval

15. A mixed-mode readout example (3) 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 ms, most due to data transmission.

16. 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

17. Analogue readout in the ALICE ITS Average power consumption: 360 mW/ch @ 1.4 ms and 2.5 Power supply (After[6]). Active shaper HAL25

18. Mixed-mode readout in the ALICE ITS The ASICs incorporates all the biasing circuitry on board and works with 4 SMD capacitors of 100 nF

19. Front-end detail(after [7] Binary readout in the ALICE ITS Scheme of an individual pixel (after [6]).

20. 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 mm in full production, 0.09 mm 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!)

21. Scaling.... However, scaling can be very beneficial also to our applications! After P. Fisher, “Readout of Pixel detectors : some thoughts on the next chip Generation”, presented at Vertex 2001.

22. 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.

23. A closer look Power dissipation in class A amplifier

24. 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

25. Disclaimer… Applications to security issues: a front-end designer point of view!

26. 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: • Detection of conventional explosives and weapon. • 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: • Exporting and adapting techniques already developed for basic research purposes. • Exporting the competence to devise new solutions.

27. 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.

28. 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: • Neutron based systems. • Gamma ray based systems. • Others.

29. 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

30. Gamma ray detectors Comparative table of Gamma ray detectors (After[7]).

31. 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.

32. Application example (1b) System layout (after[9]).

33. Application example (1c) Performance example with a Cf-252 source (after [9])

34. 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).

35. 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.

36. Application example (2c) Counter Counter Readout Counter Counter Counter

37. 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?? Basic idea: to exploit multiple scattering (the nightmare of HEP and nuclear physicists 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]. Mu-Vision [11]: funded by scientists and businessmen to develop commercial detection systems based on probing materials with cosmic rays muons

38. Proposed cargo inspection system

39. 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

40. 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)

41. 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