Jesús Soret

Time-to-Digital Converter Based on FPGA With Multiple Channel Capability

This contribution describes an accurate approach implementing a Time-to-Digital Converter using a Field-Programmable Gate Array (FPGA) device. Time differences with a FWHM better than 100 ps for 24 pairs of channels working simultaneously have been achieved. This was possible through the proper management of FPGA internal resources and by an accurate device calibration process minimizing the effect of temperature and voltage fluctuations. The system calibration results and the time differences between multiple channels are presented. The current approach suggests the possibility of carrying out precise Time of Flight (TOF) measurements with, for instance, Positron Emission Tomography (PET) systems.

Novel Wireless Sensor System for Dynamic Characterization of Borehole Heat Exchangers

The design and field test of a novel sensor system based in autonomous wireless sensors to measure the temperature of the heat transfer fluid along a borehole heat exchanger (BHE) is presented. The system, by means of two specials valves, inserts and extracts miniaturized wireless sensors inside the pipes of the borehole, which are carried by the thermal fluid. Each sensor is embedded in a small sphere of just 25 mm diameter and 8 gr weight, containing a transceiver, a microcontroller, a temperature sensor and a power supply. A wireless data processing unit transmits to the sensors the acquisition configuration before the measurements, and also downloads the temperature data measured by the sensor along its way through the BHE U-tube. This sensor system is intended to improve the conventional thermal response test (TRT) and it allows the collection of information about the thermal characteristics of the geological structure of subsurface and its influence in borehole thermal behaviour, which in turn, facilitates the implementation of TRTs in a more cost-effective and reliable way.

Timing Results Using an FPGA-Based TDC with Large Arrays of 144 SiPMs

Silicon photomultipliers (SiPMs) have become an alternative to traditional tubes due to several features. However, their implementation to form large arrays is still a challenge especially due to their relatively high intrinsic noise, depending on the chosen readout. In this contribution, two modules composed of 12 ×12 SiPMs with an area of roughly 50 mm×50 mm are used in coincidence. Coincidence resolving time (CRT) results with a field-programmable gate array, in combination with a time to digital converter, are shown as a function of both the sensor bias voltage and the digitizer threshold. The dependence of the CRT on the sensor matrix temperature, the amount of SiPM active area and the crystal type is also analyzed. Measurements carried out with a crystal array of 2 mm pixel size and 10 mm height have shown time resolutions for the entire 288 SiPM two-detector set-up as good as 800 ps full width at half maximum (FWHM).

Algorithms for the ROD DSP of the ATLAS hadronic Tile Calorimeter

In this paper we present the performance of two algorithms currently running in the Tile Calorimeter Read-Out Driver boards for the commissioning of ATLAS. The first algorithm presented is the so called Optimal Filtering. It reconstructs the deposited energy in the Tile Calorimeter and the arrival time of the data. The second algorithm is the MTag which tags low transverse momentum muons that may escape the ATLAS muon spectrometer first level trigger. Comparisons between online (inside the Read-Out Drivers) and offline implementations are done with an agreement around 99% for the reconstruction of the amplitude using the Optimal Filtering algorithm and a coincidende of 93% between the offline and online tagged muons for the MTag algorithm. The processing time is measured for both algorithms running together with a resulting time of 59.2 μs which, although above the 10 μs of the first level trigger, it fulfills the requirements of the commissioning trigger ( ~ 1 Hz). We expect further optimizations of the algorithms which will reduce their processing time below 10 μs.

A VLSI for deskewing and fault tolerance in LVDS links

The device presented at this work is a switch implemented in a 0.35 mum CMOS process for compensating the skew which affects parallel data signal transmissions and for providing fault tolerance in large scale scalable systems, for instance used in trigger farms for high energy physics experiments. The SWIFT chip (SWItch for Fault Tolerance) is part of a cluster built around commercially components which has been inspired by the LHCb experiment. The skew is extremely important because it directly affects the sample window available to the receiver logic and either forces to use quality and expensive cables in order to minimize its effects or reduces the maximum signal transmission range or distance. This problem is handled by the deskewing circuitry at the SWIFT chip, which is able to match dynamically the signal transitions at the receiver link by adding an individual delay to each input signal in steps of 100 ps for LVDS signals up to 250 MHz. The deskew module is based on full custom analog delay units plus a digital skew detector block. A 16-bit processor is implemented for processing tasks. The chip compensates dynamically skews of LVDS signals up to 250 MHz in steps of 100 ps and adds fault tolerance to the farm of PCs by allowing the bypassing of a failing compute node to which is attached

High-resolution multichannel Time-to-Digital Converter core implemented in FPGA for ToF measurements in SiPM-PET

In this contribution, Coincidence Resolving Time (CRT) results with the developed multichannel FPGA-TDC are showed as a function of different configurations for both, the sensor bias voltage and the digitizer threshold. The dependence of the CRT with the sensor matrix temperature, the amount of SiPM active area and the crystal type are also analyzed. Preliminary measurements carried out with a crystal array of 2 mm pixel size and 10 mm height have shown time resolutions for the entire 144 SiPM two-detectors ensemble as good as 800 ps.

Optimization of a Time-to-Digital Converter and a coincidence map algorithm for TOF-PET applications

This contribution describes the optimization of a multichannel high resolution Time-to-Digital Converter (TDC) in a Field-Programmable Gate Array (FPGA) initially capable of obtaining time resolutions below 100ps for multiple channels. Due to its fast propagation capability it has taken advantage of the FPGA internal carry logic for accurate time measurements. Furthermore, the implementation of the TDC has been performed in different clock regions and tested with different frequencies as well, achieving improvements of up to 50% for a pair of channels. Moreover, since the TDC is potentially going to be used in a trigger system for Positron Emission Tomography (PET), the algorithm for coincidence identification has been subjected to tests in order to estimate the impact on occupied resources and the execution time. This time has been optimized, resulting in speed improvements of up to 20% while preserving occupied resources.

Characterization of Different Cable Ferrite Materials to Reduce the Electromagnetic Noise in the 2–150 kHz Frequency Range

The gap of standardization for conducted and field coupled electromagnetic interferences (EMI) in the 2–150 kHz frequency range can lead to Electromagnetic Compatibility (EMC) problems. This is caused by power systems such as Pulse Width Modulation (PWM) controlled rectifiers, photovoltaic inverters or charging battery units in electric vehicles. This is a very important frequency spectral due to interferences generated in a wide range of devices and, specifically, communication problems in the new technologies and devices incorporated to the traditional grid to convert it into a Smart Grid. Consequently, it is necessary to provide new solutions to attenuate this kind of interference, which involves finding new materials that are able to filter the electromagnetic noise. This contribution is focused on characterizing the performance of a novel material based on nanocrystalline and comparing it to most common material compositions such as MnZn and NiZn. This research is carried out from the point of view of the manufacturing process, magnetic properties and EMI suppression ability. This last item is carried out through two analysis procedures: a theoretical method by determining the attenuation ratio by measuring impedance parameter and proposing a new empirical technique based on measuring directly the insertion loss parameter. Therefore, the main aim of this characterization process is to determine the performance of nanocrystalline compared to traditional cable ferrite compositions to reduce the interferences in this controversial frequency range. From the results obtained, it is possible to deduce that nanocrystalline cable ferrite provides the best performance to filter the electromagnetic noise in the 2–150 kHz frequency range.

Time of flight measurements based on FPGA using a breast dedicated PET

In this work the implementation of a Time-to-Digital Converter (TDC) using a Nutt delay line FPGA-based and applied on a Positron Emission Tomography (PET) device is going to be presented in order to check the systems suitability for Time of Flight (TOF) measurements. In recent years, FPGAs have shown great advantages for precise time measurements in PET. The architecture employed for these measurements is described in detail. The system developed was tested on a dedicated breast PET prototype, composed of LYSO crystals and Positive Sensitive Photomultipliers (PSPMTs). Two distinct experiments were carried out for this purpose. In the first test, system linearity was evaluated in order to calibrate the time measurements, providing a linearity error of less than 2% and an average time resolution of 1.4 ns FWHM. The second set of measurements tested system resolution, resulting in a FWHM as good as 1.35 ns. The results suggest that the coincidence window for the current PET can be reduced in order to minimize the random events and thus, achieve better image quality.

Application of a New Wireless Instrument to Characterize Thermal Properties of Ground Coupled Heat Exchangers

Abstract In this work, we report the design and laboratory test of a new instrument to measure the temperature of the heat transfer fluid along the borehole exchanger (BHE) by autonomous wireless sensor. The instrument consists of a device, which inserts and extracts miniaturized wireless sensors in the borehole with a mechanical subsystem, composed by a circulating pump and two valves. This device transmits to the sensors the acquisition configuration, and downloads the temperature data measured by the sensor along its way through the borehole heat exchanger. Each sensor is included in a sphere of 25 mm diameter and contains a transceiver, a microcontroller, a temperature sensor and a power supply. This instrument allows the collection of information about the thermal characteristics of geological structure of soil and its influence in borehole thermal behaviour, in dynamic regime, and facilitates the implementation of thermal response test (TRT) more easy and reliable.