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Xavier Llopart, CERN Vienna, Feruary 2007

Timepix, a 65k programmable pixel readout chip for arrival time, energy and/or photon counting measurements. Xavier Llopart, CERN Vienna, Feruary 2007. Outline. Medipix2 From Medipix2 to Timepix Timepix chip Electrical characterization First Images Summary. Medipix2.

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Xavier Llopart, CERN Vienna, Feruary 2007

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  1. Timepix, a 65k programmable pixel readout chip for arrival time, energy and/or photon counting measurements Xavier Llopart, CERN Vienna, Feruary 2007

  2. Outline • Medipix2 • From Medipix2 to Timepix • Timepix chip • Electrical characterization • First Images • Summary

  3. Medipix2 • Square pixel size of 55 µm • Sensitive to positive or negative input charge • Pixel by pixel detector leakage current compensation • Window in energy as precise as possible • 14-bit counter per pixel with overflow control • Count rates of 1 MHz/pixel (0.33 GHz/mm2) • 256 x 256 pixels • 3-side buttable • serial or parallel I/O

  4. 14080 m (pixel array) 16120 m 14111 m Medipix2 (II) • 6 metal layers IBM 0.25um • Serial readout <5ms@180MHz • Parallel readout <300us@120MHz (>1KHz frame !!!) • Static power consumption ~550mW • >35 Mtrts • Sensitive area ~2cm2 • Available in 2002

  5. Medipix2 collaboration • Form by 17 institutes (16 EU and 1 US) • Applications: • Dental radiography • Mammography • Angiography • Dynamic autoradiography • Tomosynthesis • Synchrotron applications • Electron-microscopy • Gamma camera • X-ray diffraction • Neutron detection • Dynamic defectoscopy • Adaptative optics • Radiation monitor • > 100 publications in the last 5 years (http://www.cern.ch/Medipix) • Medipix3 collaboration started last September (“The Medipix3 Prototype, a Pixel Readout Chip Working in Single Photon Counting Mode with Improved Spectrometric Performance”, R.Ballabriga, IEEE NSS-MIC 2006)

  6. 50um GEM Micromegas From Medipix to Timepix • A novel approach for the readout of a TPC at the future linear collider is to use a CMOS pixel detector combined with some kind of gas gain grid • Using a naked photon counting chip Medipix2 coupled to GEMs or Micromegas demonstrated the feasibility of such approach

  7. Motivation: Medipix ￫ Timepix • These experiments (by NIKHEF, Saclay and Freiburg 2004/2005 ) demonstrated that single electrons could be detected using a naked Medipix2 chip 2D • Did not provide information on the arrival time of the electron in the sensitive gas volume  3D (position + time) • The Timepix chip has been designed as an evolution of the Mpix2MXR20 with a time stamp with a tunable resolution of 100 to 10ns. • Requirements: • Keep Timepix as similar as possible to Medipix2 in order to benefit from large prior effort in R/O hardware and software. • Avoid major changes in pixel and/or readout logic – risk of chip failure due to poor mixed mode modeling. • Keep 2nd threshold if possible ￫ TOT measurement • This modification has been supported by the JRA2/EUDET Collaboration (www.eudet.org).

  8. Timepix Pixel Schematic Previous Pixel Ref_Clkb Clk_Read Mux 4 bits thr Adj Mask Mux Preamp Input Disc 14 bits Shift Register Shutter Timepix Synchronization Logic THR Shutter_int Ctest P0 Conf Testbit Polarity P1 8-bit PCR Test Input Ovf Control Ref_Clk Clk_Read Next Pixel Analog Digital

  9. Ref_Clk distribution • Power uniformly distributed over clock period ￫ minimize coupling • ~50ns to distribute the clock all over the chip • ~500mW @100MHz (simulations) Ivdd[mA]  2·f[MHz] ~50ns ~0.820mA/col  ~210mA/chip

  10. Medipix Mode TOT Mode Timepix Mode Timepix Synchronization Logic (TSL) • Each pixel can be configured independently in 3 different operation modes • TSL synchronizes the Ref_Clk with hit an Shutter • Minimized power consumption in stand-by (no hit) • Each pixel can be masked independently • Maximum number of counts￫11810 (~230µs @Ref_Clk=50MHz)

  11. Timepix Pixel Layout Timepix layout • Preamplifier: • 90-180ns peaking time (Preamp DAC) • 0.5µs-2.5µs constant current fall time Qin<10ke- (Ikrum DAC) • Sensitive to e- and h+ with leakage current compensation • Nominal gain ~16.5mV/ke- • Output voltage dynamic range ~50ke- • Discriminator: • Polarity control • 4-bit threshold adjustment DAC • Hysteresis • Pixel analog power ￫ ~6.5µW (20x55 µm2) • ~50 transistors • Pixel Configuration Register • 4 bit threshold adjustment • 2 bit pixel operation mode (P0 and P1) • 1 bit mask • 1 bit test pulse • Timepix Synchronization Logic: • Counter clock synchronization (Mode operation) • Ref_Clk pixel buffer • 14-bit shift register: • LFSR with 1 XOR tap ￫ 11810 maximum counts • Overflow control • Pixel digital ‘static’ power ￫ ~6.5µW@100MHz (35x55 µm2) • ~500 transistors

  12. Medipix ￫ Timepix Layout Mpix2MXR20 layout Timepix layout

  13. Timepix chip architecture • IBM 0.25µm CMOS • Chip architecture almost identical to Mpix2MXR20 • M0=M1=1 and Shutter ON -> FClock used as Ref_Clk • 256x256 55µm square pixels • Analog Power -> 440mW • Digital Power (Ref_Clk=80MHz) -> 450mW • Serial readout (@100MHz) -> 9.17 ms • Parallel readout (@100MHz) -> 287 µs • > 36M transistors • Chip available November 2006

  14. ‘Official’ Medipix readout systems • MUROSv2.1: • Serial readout • VHDCI cable length <3m • ~40fps @160MHz • Tunable readout clock [30-200MHz] • Already compatible with Timepix • http://www.nikhef.nl/pub/experiments/medipix/muros.html • USB1.1: • Serial readout • ~5 fps@20MHz • Not compatible with Timepix • HV generator • http://www.utef.cvut.cz/medipix/usb/usb.html MUROSv2.1 USB

  15. Pixelman Software • Compatible with Medipix2.1, Mpix2MXR20 and Timepix. • Compatible with USB and Murosv2.1 serial readout systems • Compatible with single chip or multi-chip (quad) PCBs • High flexibility: Several USBs and Murosv2.1 systems controlled simultaneously • http://www.utef.cvut.cz/medipix/Pixelman/pixelman.html

  16. Timepix wafer map • Yield (on 7 wafers): • Test includes for each chip: • Digital Test • Chip ID • Write/Read matrix test • Analog Test: • DACs scan • Tespulse Test (Medipix and TOT)

  17. Timepix electrical characterization • ‘Naked’ mounted in standard PCB • Murosv2.1 and Pixelman software • The calibration test pulse : • Dynamic range of ~40ke- • Gain ~46e-/mV (based on simulations) Standard PCB

  18. Shutter PreampOut Thr discOut CounterClk Pixel measurements • From the 2 test pixels [120:121,0] one can measure the preampOut, discOut, internal Ref_Clk and the counter clock • State Machine of the counter Modes (P0, P1) work as expected • No visible coupling of the Ref_Clk signal into the analog signals (preampOut and discOut)

  19. TOT Mode Time Mode Reconstructed analog output Shutter THL PreampOut • Combining threshold scan with arrival time and TOT mode ￫ reconstruct all pixels analog output • Amplitude and timing information is revealed for all pixels • Fantastic tool !!!

  20. ‘Reconstructed’ analog output : DACs optimization • Measurement in pixel [128-128] • ∆Ikrum, ∆Preamp and ∆Qin

  21. Different polarity (h+ and e-)

  22. Counts 97.75% 50% 2.25% THL (ke-) Counting Mode • Hole collection: • Gain ~16.5 mV/ke- • ENC~99.4 e-rms • THL DAC step ~24.7 e- • Electron collection: • Gain ~16.5 mV/ke- • ENC~104.8 e-rms • THL DAC step ~25.4 e- • Excellent linearity in both collection modes

  23. Measured TOT [µs] TOT mode • Very good linearity if Qin>Qthr+3ke- • TOT linearity up to 200ke- (simulations) • ∆TOT/TOT is <5% if Qin>Qthr+1ke- ∆TOT/TOT [%]

  24. Time arrival mode • Time-walk: Qin=Qthr + 1ke- ￫ ∞ • Measured Time-walk <50ns

  25. Timepix matrix equalization • Equalization using the noise as trigger and Medipix Mode (P0=P1=0) • The measured INL of the 4-bit DAC is < 0.8 LSB ￫ Interpolation in the equalization can be used ￫ <2min for chip equalization • Minimum detectable charge: 6 √(σENC2+ σthr2) ￫ ~650e- σ= ~31 e- σ= ~33 e- σ0=245 e- σ15=245 e- σ15=234 e- σ0=237 e- THL (e-) THL (h+)

  26. Arrival time mode • Injection of ~2ke- input pulse at Thr~=1ke- ￫ 99% pixels with 1003-1004 !!! • Injection of ~20ke- ￫ 99% pixels with 1005-1006 !!! • Matrix time-walk [(Thr+1Ke-) ￫ ∞] is <50ns at nominal settings (Ref_Clk=50MHz) • Could be improved with TOT measurement

  27. Pixel to pixel TOT gain variation Pixel to pixel TOT gain variation • The return to zero variation from pixel to pixel generates in TOT mode a pixel to pixel variation for the same global threshold • In counting mode and time arrival time this effect is not present

  28. Fixed pattern correction mask in TOT mode • A correction mask for this effect can be found by calculating the transfer function of each pixel by scanning the test pulse over a fix global threshold. Counts Energy (ke-)

  29. 10 test pulses in mixed mode

  30. Timepix with 3-GEM detector • DESY testbeam in November 2006 (A.Bamberger, M.Titov)

  31. Timepix with Micromegas • Nikhef January 2007 (thanks to J.Timmermans)

  32. Medipix2 vs Timepix

  33. Timepix chip is a modification of the Medipix2 chip to gives arrival time information. A distributed clock is used as time reference. 3 selectable operation modes per pixel. Chip works as expected and already first results (GEMs and Micromegas) show very ‘exciting’ results First Si assemblies available in less than 1 month ￫ Absolute calibration using X-ray sources. Conclusions and Future plans

  34. Online Timepix operation demo available…

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