W. Shen

Characterisation studies of silicon photomultipliers

This paper describes an experimental setup that has been developed to measure and characterise properties of silicon photomultipliers (SiPM). The measured SiPM properties are of general interest for a multitude of potential applications and comprise the photon detection efficiency (PDE), the voltage dependent cross-talk and the after-pulse probabilities. With the described setup the absolute PDE can be determined as a function of wavelength covering a spectral range from 350 to 1000 nm. In addition, a method is presented which allows to study the pixel uniformity in terms of the spatial variations of sensitivity and gain. The results from various commercially available SiPMs—three HAMAMATSU MPPCs and one SensL SPM—are presented and compared.

Time based readout of a silicon photomultiplier (SiPM) for time of flight positron emission tomography (TOF-PET)

Time of flight (TOF) measurements in positron emission tomography (PET) are very challenging in terms of timing performance, and should achieve ideally less than 100ps FWHM precision. We present a time-based differential technique to read out SiPMs that has less than 25ps rms electronic jitter. The novel readout is a fast front end circuit (NINO) based on a first stage differential current mode amplifier with 20Ω input resistance. Therefore the amplifier inputs are connected differentially to the SiPMs anode and cathode ports. The leading edge of the output signal provides the time information, while the trailing edge provides the energy information. Based on a Monte Carlo photon-generation model, SPICE simulations were run with a 3×3mm2 SiPM-model, read out with a differential current amplifier. The results of these simulations are presented here and compared with experimental data obtained with a 3×3×15mm3 LSO crystal coupled to a SiPM. The measured time coincidence precision is interpreted by the combined Monte Carlo/SPICE simulation, as well as by Poisson statistics.

EndoTOFPET-US: a novel multimodal tool for endoscopy and positron emission tomography

The EndoTOFPET-US project aims to develop a multimodal detector to foster the development of new biomarkers for prostate and pancreatic tumors. The detector will consist of two main components: an external plate, and a PET extension to an endoscopic ultrasound probe. The external plate is an array of LYSO crystals read out by silicon photomultipliers (SiPM) coupled to an Application Specific Integrated Circuit (ASIC). The internal probe will be an highly integrated and miniaturized detector made of LYSO crystals read out by a fully digital SiPM featuring photosensor elements and digital readout in the same chip. The position and orientation of the two detectors will be tracked with respect to the patient to allow the fusion of the metabolic image from the PET and the anatomic image from the ultrasound probe in the time frame of the medical procedure. The fused information can guide further interventions of the organ, such as biopsy or in vivo confocal microscopy.

Silicon Photomultiplier integrated readout chip (SPIROC) for the ILC: Measurements and possible further development

The SPIROC chip is a dedicated very front-end ASIC chip for an ILC hadronic calorimeter technical prototype with Silicon Photomultiplier (or MPPC) readout. This ASIC is due to equip a 2,000-channel demonstrator in 2009. The SPIROC chip is the successor of the ILC SiPM ASIC presently used for the ILC AHCAL physics prototype, incorporating additional features like auto-triggering, pipelines, digitization as well as power pulsing. Realized in 0.35μm SiGe technology, it is designed in order to fulfill ILC final detector requirements of large dynamic range, low noise, low power consumption, high precision and large channel numbers. The SPIROC is a 36-channel chip. Each channel has bi-gain amplification, auto-triggering capability, a 16-bit depth analog memory array and a 12-bit wilkinson ADC. It allows time and charge measurements at the same time with digitized data results. The digitization is controlled and read out by the digital part of the chip. After the submission in June 2007, extensive measurements have been carried out to characterize the chip. This chip has been proven to be successful in calorimeter calibration as well as real physics experiments. Besides of the affirming measurement results, possible improvements are proposed in order to make the chip even more versatile in dealing with a large variety of Silicon Photomultipliers.

STiC ? a mixed mode silicon photomultiplier readout ASIC for time-of-flight applications

STiC is an application specific integrated circuit (ASIC) for the readout of silicon photomultipliers. The chip has been designed to provide a very high timing resolution for time-of-flight applications in medical imaging and particle physics. It is dedicated in particular to the EndoToFPET-US project, which is developing an endoscopic PET detector combined with ultrasound imaging for early pancreas and prostate cancer detection. This PET system aims to provide a spatial resolution of 1 mm and a time-of-flight resolution of 200 ps FWHM. The analog frontend of STiC can use either a differential or single ended connection to the SiPM. The time and energy information of the detector signal is encoded into two time stamps. A special linearized time-over-threshold method is used to obtain a linear relation between the signal charge and the measured signal width, improving the energy resolution. The trigger signals are digitized by an integrated TDC module with a resolution of less than 20 ps. The TDC data is stored in an internal memory and transfered over a 160 MBit/s serial link using 8/10 bit encoding. First coincidence measurements using a 3.1 × 3.1 × 15 mm3 LYSO crystal and a S10362-33-50 Hamamtsu MPPC show a coincidence time resolution of less than 285 ps. We present details on the chip design as well as first characterization measurements.

STiC - A mixed mode chip for SiPM ToF applications

STiC is a mixed mode 16-channel ASIC chip in UMC 0.18 /Lm CMOS technology aiming at Silicon Photomultiplier (SiPM) readout with optimal timing resolution. It is designed for ToF measurements in HEP and medical imaging applications and dedicated in particular to the ENDOToFPET·US project, which aims at providing a powerful endoscopic Time· of-Flight PET system for early prostate and pancreas cancer diagnostics. The goal of this endoscopic system is to provide a spatial resolution of the order of 1 mm and a Time-of-Flight resolution of 200 ps FWHM. The STiC chip has a differential structure. However, SiPMs can be connected either differentially or single-endedly. The timing and charge information of the input signal - both required for a high-resolution ToFPET system - are encrypted into two time stamps and processed later by an embedded TDC module with a timing resolution of better than 20 ps. The digitized data are stored first on an on-chip SRAM block and then transferred via a 160 MBit LVDS serial link using 8/10-bit encoding. The simulated single pixel timing jitter is less than 15 ps for Hamamatsu SI0362-11-50 MPPCs. A special linearization method has been used to obtain a linear charge response in a very wide range. The total power consumption is about 20 m W per channel. Design details as well as first measurement results will be presented.

The proposed trigger-less TBit/s readout for the Mu3e experiment

The Mu3e experiment searches for charged lepton flavor violation in the rare decay μ→eee with a projected sensitivity of 10−16. A precise measurement of the decay product momenta, decay vertex and time is necessary for background suppression at rates of 109 muons/s. This can be achieved by combining an ultra-lightweight pixel tracker based on HV-MAPS with two timing systems. The trigger-less readout of the detector with three stages of FPGA-boards over multi GBit/s optical links into a GPU filter farm is presented. In this scheme data from all sub-detectors is merged and distributed in time slices to the filter farm.

STiC2 - characterization results of a SiPM readout ASIC for time-of-flight applications

STiC is a mixed-mode readout ASIC for silicon-photomultipliers (SiPM) developed in the framework of the EndoToFPET-US project. The chip has been designed in the UMC 0.18 μm technology and aims to provide an optimal timing resolution to Time-of-Flight measurements in medical imaging and particle physics applications. The differential design of the analog input stage rejects noise from the large integrated digital part as well as external sources. The chip allows either a differential or a single-ended readout of the sensors. The time and charge information of the input signal is converted into two time stamps which are digitized by an integrated TDC module with a time binning of 50 ps. A special linearized Time-over-Threshold method has been implemented to provide a linear response to the signal charge in a wide range. The digitized event information is stored in a 64-word FIFO memory and transmitted every 6.4 μs to an external DAQ system using a 160 MBit=s LVDS serial link with 8/10-bit encoding. Characterization measurements show a trigger jitter of σ <; 30 ps for input signals larger than 3 pC injected over a 33 pF capacitor. A measurement using 3.1 × 3.1 × 15mm3 LYSO crystals and Hamamatsu MPPC (S10362-33-50C) sensors to detect coincidence photons from positron annihilations shows an energy resolution of ~ 12% for the 511 keV peak and a coincidence time resolution of 220 ps FWHM. We present details of the ASIC design as well as characterization measurements.

A dedicated readout ASIC for Time-of-Flight Positron Emission Tomography using Silicon Photomultiplier (SiPM)

STiC is a mixed-mode Application Specific Integrated Circuit (ASIC) for Silicon Photomultiplier (SiPM) readout with very high timing resolution. It is designed for the Time-of-Flight (ToF) measurement in Positron Emission Tomography (PET) and in high energy physics experiments. STiC is dedicated particularly to the EndoTOFPET-US project, which is developing and building a multi-modal instrument combing ToFPET and ultrasound endoscopy for the development of new biomarkers for pancreas and prostate oncology. A 64-channel prototype (STiC v3) has been developed and produced in 0.18μm UMC CMOS technology. A fully differential analog front-end has been developed to suppress the common-mode noise from both the on-chip digital part and the outer sources, while it allows for both differential and single-ended readout connection schemes with SiPM. A digital-to-analog converter on the input stage tunes the SiPM bias voltage with a range of ~ 900 mV, providing the possibility to compensate the variation on the breakdown voltage of the connected SiPMs. A linearized time-over-threshold method has been implemented to provide better energy resolution than the conventional ToT method. The time and energy information are converted into two time stamps, which are digitized by a build-in TDC with time binning of 50.2 ps. A dedicated digital part has been developed for chip configuration with a Serial Peripheral Interface and for data transmission to an external Data Acquisition System using a 160 MBit/s LVDS serial link with 8/10-bit encoding. Measurements have shown a time jitter <; 20 ps on the analog front-end and a time jitter of ~ 37 ps on the TDC and digital part. A Coincidence Time Resolution of ~ 214 ps FWHM has been obtained by STiC v3 with 3.1 × 3.1 × 15 mm2 LYSO:Ce crystals and Hamamatsu MPPCs (S12643-050CN(x)). Here we present the details of the ASIC design, measurement results as well as the 128-channel front-end module for EndoTOFPET-US project.

Towards a time-of-flight positron emission tomography system based on Multi-Pixel Photon Counter read-out

We present the first commissioning data of our TOF-PET test device featuring MPPC read-out of small size LFS crystals. We discuss the characteristics of the test device and present results from two different multi-channel read-out ASIC chips which offer a high timing performance.