Electronics for large LAr TPC’s

1. Electronics for large LAr TPC’s F. Pietropaolo (ICARUS Collaboration) CRYODET Workshop LNGS, 13-14 March 2006

2. Outline • The ICARUS front-end electronics • Layout in T600 module (analogue + digital) • Performance and limitations • Possible upgrades for multi-kton detectors • Alternatives solutions • Front-end inside vs outside LAr • Analog-to-digital serial converter • Summary CryoDet workshop, LNGS

3. The ICARUS T600 experience • The T600 DAQ system (5·104 channels), designed in Padova, engineered and built by CAEN, has proven to perform satisfactory during the 2001 test run in Pavia. • It consists of an analogue front-end followed by a multiplexed AD converter (10 bit) and by a digital VME module performing local storage, hit finding and data compression. • From the experience gained with the T600 operation, an R&D phase is underway in view of an upgrade for a multi-kton detector with ~ n·105 channels (better S/N, larger integration, lower cost). CryoDet workshop, LNGS

4. The ICARUS read-out principle m.i.p. ionization ~ 6000 e-/mm Time Edrift ~ 500 V/cm Drift direction Hit finder Mux Memory 8:1 FADC 400ns n x 4kB multi-event circular buffer Low-noise amplifiers Continuous waveform recording To storage Daedalus Front-end CryoDet workshop, LNGS

5. The induction signals Ionizing track Induced currentInduced charge Electrons path T=0 Edrift Drift u-t view E1 Induction 1 v-t view d E2 Induction 2 w-t view Charge = ampl. Charge = area d Collection p Drift timeDrift time • ICARUS T600: three wire planes (pitch 3mm, separation 3mm) Edrift = 500 V/cm Mip signal ~ 12000 e- (inc. recombinantion) Electron drift velocity ~ 1.5 mm/s Typical grid transit time ~ 2-3 s CryoDet workshop, LNGS

6. Requirements for the preamplifier • Need of very low noise amplifier: • No amplification around sense wires • Induced charge ~ 104 electrons • Large input capacitance (CD) • Wires (20 pF/m) + cables (50 pF/m) • In T600 CD ~ 300-400pF • Serial noise (proportional to CD) dominates over parallel noise (proportional only to signal bandwidth) • High trans-conductance (gm) input device required to ensure acceptable Signal-to Noise level (S/N ~ 10) CryoDet workshop, LNGS

7. Choice of the active input device • Bipolar transistors • gm ≈ 400mS @ Ic ≈ 10 mA (Amplification merit factor gm·Zout ≈ 3-4·105) • BUT: parallel noise density ≈ 2 pA / √Hz too high (with a typical LAr signal bandwidth of ~ 1 MHz gives unacceptable noise contribution) • VLSI-CMOS • Extremely low gm • jFET • Good gm ≈ 40mS @ Ids ≈ 10 mA (Amplification merit factor gm·Zout ≈ 3-4·104) • negligible parallel noise density ≈ 0.001 pA / √Hz ICARUS choice since 1986: charge sensitive preamplifier with high gm jFET input stage CryoDet workshop, LNGS

8. The ICARUS T600 preamplifier Two versions: “quasi-current” mode: RfCf ≈ 1.6s (collection + first induction) “quasi-charge” mode: RfCf ≈ 30s (mid induction) • Custom IC in BiCMOS technology • Classical Radeka integrator • External input stage jFET’s • Two IF4500 (Interfet) or BF861/2/3 (Philips) in parallel to increase gm (50-60 mS) • External feed-back network • Allow sensitivity and decay time optimization • High value f.b. resistor (100M) reduce parallel noise • External baseline restorer circuit • Two channels per IC • Identical symmetrical layout guarantees identical electrical behavior Sensitivity ≈ 6 mV/fC Dynamic range > 200 fC Linearity < 0.5% @ full scale Gain uniformity < 3% E.N.C. ≈ (350 + 2.5 x CD) el ≈ 1200 el. @ 350pF Power consumption ≈ 40 mW CryoDet workshop, LNGS

9. Layout of front-end electronics H.V. (<±500 V) UHV Feed-through (18x32ch.) VME board (18/crate) Liquid argon Gas Sense wires (4-9m, 20pF/m) 4 Multiplexers (400ns x 8ch.) Twisted pair cables (~5m, 50pF/m) 10bit FADC 400ns sampling 1mV/ADC Front-end amplifiers (32/board) Decoupling Boards (32 ch.) ICARUS T600: ~ 54000 channels — 1720 boards — 96 crates Cost of the full electronic chain: ~ 80 € / channel CryoDet workshop, LNGS

10. The ICARUS T600 read-out chain CAEN-V789 board: 2 Daedalus VLSI * 16 input channels (local self-trigger & zero suppression) + memory buffers + data out on VME bus Signal UHV feed-through: 576 channels (18 connectors x 32) + HV wire biasing Decoupling board: HV distribution and signal input CAEN-V791 board: 32 pre-amplifiers + 4 multiplexers (8:1) + 4 FADC’s (10 bits - 20 MHz) CryoDet workshop, LNGS

11. The T600 electronic racks CryoDet workshop, LNGS

12. The analogue board V791 FADC’s Multiplexers Digital link Preamplifiers BiCMOS IC layout Input signal connector Output of analogue sum Shielding of front-end CryoDet workshop, LNGS

13. Performance of the V791 boards 128 wires/view 1024 samples 400 ns/sample V791C V791Q Mid. Induction Collection 1st Induction 1st Induction CryoDet workshop, LNGS

14. RMS noise on T600 = 1.3 - 1.7 ADC counts (due to difficult environment in Pavia) Performance of the V791C board • Single wire waveforms (horiz. axis unit = 400 ns) Test pulse (6 mm m.i.p) 24 ADC counts FWHM ≈ 5 µs m.i.p. ≈ 12 ADC counts (3 mm) FWHM ≈ 5 µs Collection 1st Induction Noise RMS ≈ 1.3 ADC counts Coherent noise due to layout not negligible! CryoDet workshop, LNGS

15. Pulse height & shape from mid. plane wires very similar to those from collection plane wires. High frequency S/N also comparable. Low frequency minimized by baseline restorer. Performance of the V791Q board • Single wire waveforms (horiz. axis unit = 400 ns) Mid. Induction Test pulse (6 mm m.i.p.) 24 ADC counts RC ≈ 30 µs m.i.p. ≈ 10 ADC counts (3 mm) FWHM ≈ 5 µs Noise RMS (h.f.) ≈ 1.2 ADC counts Low frequency noise visible but not dangerous! CryoDet workshop, LNGS

16. Collection view Events from T300 semi module Drift time (1.5m) Wire numbering (4.5m) Induction2 view Drift time (1.5m) Wire numbering (4.5m) CryoDet workshop, LNGS

17. Possible upgrades • In a multi-kton LAr-TPC with the ICARUS read-out principle we can foresee • S/N close to T600 • Longer electrodes (larger input capacitance, more electronic noise) • But probably larger electrode pitch (more input charge) • Larger number of channels (~ n•105) • Require integration, cost reduction • Present overall architecture fully satisfactory • Improvement will focus on • Input stage jFET • Technology still state of the art • Optimization of number of input jFET to larger input capacitance • Review IC design - Integrate more channels • BiCMOS technology evolved since last IC design • Careful study of layout topology • Development of new hybrid sub module • Hosting more amplification channels (e.g. 4 - 8) • And, possibly, the analogue-to-digital converter stage CryoDet workshop, LNGS

18. Electronics in LAr • Deeply investigated within ICARUS collaboration (since 1988) • Limited choice of active devices working at LAr temperature • GAs-jFET (High Electron Mobility Transistor technology) • Silicon jFET (High Resistive Substrate technology) • Expected characteristics: • Better S/N due to improved gm at cryogenic temperature • Reliability at LAr temperature • Availability on the market U310 jFET Carrier mobility decrease Pinch-off increase CryoDet workshop, LNGS

19. Pro & Contra • Advantages • Reduction of input capacitance due to cable absence • Reduction of micro-phonic noise (detector = Faraday cage) • Intrinsic improvement of S/N due to larger jFET gm at cryogenic temperature • Disadvantages • Inaccessibility during detector operation • Need of careful selection of components, extensive burn-in and temperature cycles before installation to minimize components failure • Design architecture and technology restricted by limited choice of active components • Limit on power dissipation (< 100 mW/mm2 to avoid LAr boil-off) CryoDet workshop, LNGS

20. The TOTEM architecture • Charge Integrator made on Thick Film Hybrid technology with discrete jFET only • Minimum active and passive components • Ability to drive long transmission line • Reduced power consumption • Minimum cable connections • Current signal from Positive Power Supply • Common Negative polarization • Characteristics • Optimized for low detector capacitance (IF1330) Sensitivity ≈ 0.45 mV/fC (0.9 A/fC) Dynamic range ±1.5 pC Linearity < 0.5% @ full scale Input impedance ≈ 420  Input capacitance ≈ 20 pF E.N.C. ≈ (390 + 7 x CD) el Power consumption ≈ 11 mW CryoDet workshop, LNGS

21. Events with electronics in LAr • Extensively used on the 50 liter LAr-TPC • Wire capacitance: ~ 15 pF (horiz. axis unit = 400 ns) Collection mip ≈ 10 ADC counts (2.54 mm) FWHM ≈ 6 µs Collection Noise RMS ≈ 0.7 ADC counts Induction Negligible low frequency noise ! CryoDet workshop, LNGS

22. The ICARUS experience • Electronics in LAr studied for sake of completeness • Not a viable solution for large scale detectors • Inaccessibility, poor integration, cost • However • TOTEM design could be improved • HEMT replacing silicon jFET • jFET matrix on single chip • Technology commercially available for low temperature application • E.g. INTERFET IPA300 amplifier (serial noise density = 0.6 nV / √Hz, 80 mW dissipation) CryoDet workshop, LNGS

23. Analog-to-digital conversion • Two sets per V789 board (32 ch.) • Total bandwidth = 800 Mbit/s • Present architecture • Serves sets of 16 channels through analogue multiplexers and 10 bit FADC’s • Trade-off between sampling speed and price • FADC sampling rate 20MHz interleaved • 400 ns sampling time / channel • 40MHz digital output • Dissipated power ~ 500 mW • Components cost ~40 € / 16 channels CryoDet workshop, LNGS

24. Compact serial AD converter • New architecture based on 1-bit serial converter • Interesting characteristics • No need for multiplexing • Very low number of components • Resolution better than 10 bit • Commercially available chip • Low price (< 1 € / channel) • Basic structure • Four QUAD FLATPACK 4x4 mm2 components plus few glue logic • Sampling rate = 16 MHz • Dissipated power = 400mW • Data reconstruction • Simple FIR filters could be implemented • In pipeline on FPGA / DSP • Off line after data storage • Serving multiples of 16 channels • Test underway of 16 channel prototype boards fully compatible with present ICARUS data link • Total bandwidth = 256 Mbit/s • Upgradable to 800 Mbit/s if sampling rate increased to 25 MHz and 32 channels CryoDet workshop, LNGS

25. Serial ADC frequency response 16 sample FIR comb filter equivalent to 10 bit resolution 8 sample FIR comb filter equivalent to 8 bit resolution 25 MHz 16 MHz Typical ICARUS signal bandwidth (~ 1 MHz) better matched in 25 MHz case. Marginal in the 16 MHZ case CryoDet workshop, LNGS

26. Simulations • Typical ICARUS signal waveform (~3s width) digitized with Serial AD converter • FIR comb filter applied to recover signal shape (16 sample width) • 10 bit equivalent resolution • 1 bit quantization noise • Continuous reconstruction (useful feature for signal analysis) Input waveform Continuous reconstruction 400ns sampled (cfr. FADC) 16 MHz 25 MHz Slight pulse height reduction but area (= charge) unchanged CryoDet workshop, LNGS

27. Signals from LAr • LAr signal waveforms (from oscilloscope) digitized with Serial AD converter simulator • FIR comb filter applied to recover signal shape (16 sample width) • Quantization noise well within analogue noise level Input waveform Continuous reconstruction 400ns sampling 16 MHz 25 MHz CryoDet workshop, LNGS

28. Prototype board • 16 channels • 16 MHz sampling rate • Data link compatible with ICARUS DAQ • Effective throughput 256 Mbit/s Charge sensitive preamplifiers Digital link 4 x 4 channel serial AD converters CryoDet workshop, LNGS

29. First signals from prototype • Test pulse injected on on-board preamplifiers • Digitized signal recorded with ICARUS DAQ • Off-line signal reconstruction with FIR comb filter (16 sample width) Input waveform Continuous reconstruction 400ns sampling 16 MHz Zoom of gray shaded area High preamp. noise due to present board layout (analogue/digital interference) CryoDet workshop, LNGS

30. Summary • The ICARUS R&D on electronics for large LAr-TPC’s • Upgrade of the analogue front-end • VLSI-CMOS technology for high channel integration excluded by simple S/N requirements • Review of amplifier IC design could allow integrating more than two channel per chip • Use of HEMT at input could help improving S/N • Possible alternative solution • Development of a completely new cold amplifier (hybrid based on TOTEM structure with jFET matrix or HEMT) for better S/N • Major drawback: inaccessibility, component reliability, cost • Upgrade of Analogue-to-digital conversion • Serial-converter: promising alternative to Multiplexer + Flash ACD • Intrinsically simpler,more compact, cheaper • Comparable bandwidth and signal resolution • Review of the data link with digital buffers • Study the recent optical link development at LHC experiments to help defining a suitable solution for the LAr-TPC environment CryoDet workshop, LNGS