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Time Pick -off Techniques

Time Pick -off Techniques. Jean-Francois Genat CNRS/IN2P3/LPNHE Paris IEEE Nuclear Science Symposium and Medical Imaging Conference October 23d 2011, Valencia, Spain.

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Time Pick -off Techniques

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  1. Time Pick-off Techniques Jean-FrancoisGenat CNRS/IN2P3/LPNHE Paris IEEE Nuclear Science Symposium and Medical Imaging Conference October 23d 2011, Valencia, Spain

  2. The lecture will review the major limitations affecting timing measurements and the techniques to overcome them.Perspectives to achieve time accuracy in the picosecond regime will be discussed Outline • Fast signals • Threshold techniques • Sampling techniques • Conclusion Timing Pick-off Techniques, October23d 2011, Valencia, Spain

  3. Fast detectorsand signals Moving charges: i(t)= n(t) q v(t) Rise-timei’(t)= q [ n(t) v’(t) + n’(t) v(t)] In order to minimize rise-time, maximize: nelectron multiplication PMTs, MCPs dv/dtqE/m electric field (in vacuum) dn/dtprimary ionisation, multiplication v t . qE /m electric field Bias Fast: - Vacuum devices - Electron multiplication - Low capacitance - High electric fields Timing Pick-off Techniques, October23d 2011, Valencia, Spain

  4. Fast detectors Nanosecond: Photo-Multipliers Sub-nanosecond: Silicon Photo-Multipliers Pico-second ? Micro-Channel Plates, Streak camera Rise-time Timing Regular PMTs 2-5ns 500 ps Silicon • APDs, PIN300 ps 50 ps • Silicon PMs 700 ps 100 ps • 3D Silicon 500ps ? Vacuum • Multi-anode/mesh PMTs 200ps 50 ps • MCP PMTs 150 ps 20-30 ps • Multi anodes MCP PMTs 30 ps ? 1 ps ? Timing Pick-off Techniques, October23d 2011, Valencia, Spain

  5. Fastsignals 10% 90% Rise-time • - Rise-time • Waveform • Signal to Noise • Leadingedgeis • relevant for timing • (first electrons) Example: 5 x 5 cm2 Micro-Channel Plate signal Rise time = 400 ps Bandwidth = 0.35/rise-time ~ 1 GHz Timing Pick-off Techniques, October23d 2011, Valencia, Spain

  6. - Obtain digital signalsfromanalog detector pulses and feed a Time to Digital Coder - Sample and digitize, thenprocessdigitally to get the difference Stop-Start Timing Measurements Oscilloscope traces for timing signalsdriving a TDC. Dt= 10ns Waveformsdigitizedwith a digital oscilloscope. ICscan do thistoday Timing Pick-off Techniques, October23d 2011, Valencia, Spain

  7. Timing Measurements Electronics gain-bandwidth should match: • Detector sensitivity • Detector rise-time Example: Multi-anodes MCP PMTs: Rise-time: 25ps Corresponding Bandwidth: 15 GHz Timing Pick-off Techniques, October23d 2011, Valencia, Spain

  8. Time Pick-off Techniques Outline • Fast signals • Threshold techniques • Sampling techniques (See Eric Delagnes) • Conclusion Timing Pick-off Techniques, October23d 2011, Valencia, Spain

  9. Single threshold pick-off Leading edge Threshold: Time spread proportional to noise and rise-time See Angelo Rivetti ‘s lecture for CMOS IC discriminators implementations Timing Pick-off Techniques, October23d 2011, Valencia, Spain

  10. Single threshold pick-off noise sA Slope dV/dt Threshold st Effects of Rise-time and Noise on Timing resolution Timing Pick-off Techniques, October23d 2011, Valencia, Spain

  11. Effects of amplitude and rise-time with single threshold Amplitude and/or Rise-time spectra translate into time spread Timing Pick-off Techniques, October23d 2011, Valencia, Spain

  12. Improved Time Pick-off Techniques Multi-threshold Leading edge Constant-fraction Constant fraction Leading edge errors Pulse sampling and Waveform analysis Extrapolated time ANALOG DIGITAL Sample, digitize, Fit to the (known) waveform Get time and amplitude 12 Timing Pick-off Techniques, October23d 2011, Valencia, Spain

  13. Constant Fraction If rise-time proportional to amplitude, use constant-fraction Constant fraction 1 Leading edge Leading edge Leading edge errors OK If rise-time does not depend If pulse shapeindependentupon upon amplitude. Leadingedge OK amplitude, use Constant Fraction But detector maybeundersaturation Timing Pick-off Techniques, October23d 2011, Valencia, Spain

  14. Constant Fraction implementation • Compare the delayed signal with the attenuated signal (or zero-cross the difference) • Need to enable the zero crossing (undefined state before and after operation) • (See A. Rivetti’s lecture) • A regular discriminator can be used, the delay line is critical (delay, bandwidth), • In ICs, it can be implemented with a low pass filter (See A. Rivetti’s lecture) • Three parameters: • Trigger threshold • Delay • Fraction • Maximize slope at zero-crossing • Carefully optimize parameters wrt signals properties • Not trivial ! • H. Spieler [IEEE NS 29 June 1982 pp1142-1158 ] • T.J. Paulus [IEEE NS 32 June 1985 pp 1242-1249] Timing Pick-off Techniques, October23d 2011, Valencia, Spain

  15. Timing resolutionusingWaveformSampling where Since whith and (Stefan Ritt) Timing Pick-off Techniques, October23d 2011, Valencia, Spain

  16. Other effects Walk: Discriminator delay (walk) depends on slope across threshold Resulting rise-time is (detector rise-time + amplifier rise-time) Use an appropriate (gain x bandwidth) technology Timing Pick-off Techniques, October23d 2011, Valencia, Spain

  17. Zerocrossing • Use zero-crossing of signal derivative • Detects signal’s maximum Signal Reject noise from signal derivative delay Timing Pick-off Techniques, October23d 2011, Valencia, Spain

  18. Double Threshold • High threshold to trigger • Low threshold to time Low thresh Delay Signal Hi thresh Avoids noise on low threshold Decision on very first signal rise delay Timing Pick-off Techniques, October23d 2011, Valencia, Spain

  19. Single threshold + Peak measurement • If the peak amplitude is measured, single threshold can be compensated off-line for rise-time, and even lead to better results than constant fraction Timing Pick-off Techniques, October23d 2011, Valencia, Spain

  20. Time Pick-off Techniques Outline • Fast signals • Threshold techniques • Sampling techniques • Conclusion Timing Pick-off Techniques, October23d 2011, Valencia, Spain

  21. Waveform Sampling (See Eric Delagnes talk) 2 12 25 80 128 50 32 … Waveform analysis 21 Timing Pick-off Techniques, October23d 2011, Valencia, Spain

  22. Sampling Electronics for Micro-Channel Plate Detectors Store the full detector information as with a digital oscilloscope: - Detector + electronics noise >> quantization noise (LSB/√12) Sampling frequency > 2 x full Analog Bandwidth (Shannon-Nyquist) Ideal approach: Digitize on the fly, if the two above conditions can be fulfilled. If not, loss of precision due to A/D conversion and/or loss of timing information Noise as small as possible 2 GHz Slope as steep as possible Fourier spectrum of a 2”x 2” MCP signal Timing Pick-off Techniques, October23d 2011, Valencia, Spain

  23. Waveform Sampling Analysis(see Eric Delagnes talk) Many techniques B. Cleland and E. Stern, BNL Signal Templates Real MCP Laser data Extract precise time and amplitude from optimal filtering (minimization of c2) evaluated with a fit to a waveform template deduced from averaged measurements 23 Timing Pick-off Techniques, October23d 2011, Valencia, Spain

  24. Timing resolutionusingWaveformSampling where Since whith and (Stefan Ritt) Timing Pick-off Techniques, October23d 2011, Valencia, Spain

  25. Sampling Electronics for Micro-Channel Plate Detectors A/D converters do not fit the need. State of the art: 8-bit 1GS/s 10-bit 300 MS/s 16-bit 160 MS/s Need at least 5 GS/s sampling rate,10-12bit There is no ! Fast analog storage and slower digitization, if rate allows, or dead-time acceptable See Eric Delagnes talk Apply the best timing algorithm suited to the detector, get the charge for free Timing Pick-off Techniques, October23d 2011, Valencia, Spain

  26. Waveform Sampling: Timing Resolution vs Sampling Rate 26 Timing Pick-off Techniques, October23d 2011, Valencia, Spain

  27. Synthesized signals used for simulations 280ps rise-time (Micro-Channel Plate like) Noise: 50% MCP noise + 50% White noise 27 Timing Pick-off Techniques, October23d 2011, Valencia, Spain

  28. Waveform Sampling : Timing resolution vsAnalog Bandwidth and Signal to Noise Timing Pick-off Techniques, October23d 2011, Valencia, Spain

  29. Waveform sampling: Timing resolution vs Sampling rate / Analog Bandwidth (simulation) Timing resolution vs Sampling rate / Analog bandwidth 29 Timing Pick-off Techniques, October23d 2011, Valencia, Spain

  30. Timing Pick-off methods compared (simulation) Time resolution vs Number of photo-electrons zoom Inputs Timing Pick-off Techniques, October23d 2011, Valencia, Spain

  31. System issues Drifts due to environmental conditions Power supplies drifts and noise Cables/fibers instabilities - Cable has shorter group delay, and even higher bandwidth, may pick-up noise - Micro-coax makes a come-back Timing Pick-off Techniques, October23d 2011, Valencia, Spain

  32. CMOS ICs Technologies CMOS bandwidths from 90 to 45 nm technology nodes (ITRS 2005) Timing Pick-off Techniques, October23d 2011, Valencia, Spain

  33. Time Pick-off TechniquesOutline • Fast signals • Threshold techniques • Sampling techniques • Conclusion Timing Pick-off Techniques, October23d 2011, Valencia, Spain

  34. Conclusion Timing pick-off requires dedicated analog front-end electronics matched with the signal characteristics in terms of noise and bandwidth. Many techniques exist matched to different detector and environment conditions Fast analog and digital challenging signal processing techniques are needed for precision timing measurements. Knowledge of the intrinsic signal properties (waveform, bandwidth, noise) is mandatory. Choice can also be dictated by environment constraints such as event rate, number of channels, availability of digital signal processing and ASIC design means, and cost. 34 Timing Pick-off Techniques, October23d 2011, Valencia, Spain

  35. Extra slides 35 Timing Pick-off Techniques, October23d 2011, Valencia, Spain

  36. out1 out2 In1 In2 Time arbitration Six transistors implementation in CMOS Metastability issues when driven with the same input [V. Gutnik et al. MIT, IEEE 2000 Symp. on VLSI Circuits] Timing Pick-off Techniques, October23d 2011, Valencia, Spain

  37. Waveform Sampling benefits Pulse sampling and waveform analysis for 2D delay line readout Pico-second timing with fast detectors Timing along the strip, a few ps obtained (< 1mm) Centroids perpendicular Resolve pile-up, mishappened pulses Large area detectors can be read in series: 37 Timing Pick-off Techniques, October23d 2011, Valencia, Spain

  38. Fast Micro-Channel Plate signals 11 mm diameter Micro-Channel Plate signal Signal bandwidth: 10 GHz Single Photoelectron Time Transit Spread: 10 ps TTS= 10ps From Photek Timing Pick-off Techniques, October23d 2011, Valencia, Spain

  39. Micro-Channel Plate Detectors Photo-cathode 1st gap pores 2d gap 200 V Pore diameter: a few mm 1- 2kV 10 mm 200 V Pore diameter 3-25 mm Pore aspect ratio: 1:50 Anodes (1.6 x 1.6mm2 pixels) 39 Timing Pick-off Techniques, October23d 2011, Valencia, Spain

  40. Response dB Micro-Channel plate structure Boardonly Board+ electronics -5dB -10dB Example: Large Area PicosecondPhoto-detectors Anodes striplines Frequency1GHz Crosstalk % 3% 2% 1% 1st neighbor 2d neighbor 3d neighbor Normalized injection position FastReadoutsampling Electronics (130nm CMOS) Bandwidth and crosstalkevaluation Timing Pick-off Techniques, October23d 2011, Valencia, Spain

  41. Transmission Line ReadoutPosition Resolution 50 Photo-Electrons Oscilloscope Tektronix TDS6154C 25 mm pore MCP signal at the output of a ceramic transmission line Laser 408nm, 50W, no amplification 41 Timing Pick-off Techniques, October23d 2011, Valencia, Spain

  42. Fast Sampling Switched Capacitor Array Timing generator A/D converter Trigger Analog input Switched capacitor array • Sampling frequency • Analog bandwidth • Analog dynamic range • Depth • Readout frequency • Read/Write State of the art: 250nm CMOS 6ps rms G. Varner, S. Ritt Chicago-Hawaii: - 130nm CMOS - 15 GS/s sampling rate - Foreseen timing resolutions of a few ps 42 Timing Pick-off Techniques, October23d 2011, Valencia, Spain

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