S. Michelis

Optimization of Shielded PCB Air-Core Toroids for High-Efficiency DC–DC Converters

The paper describes the design of optimized printed circuit board (PCB) air-core toroids for high-frequency dc-dc converters with strict requirements in terms of volume and noise. The effect of several design parameters on the overall inductor volume, on dc and ac winding resistance, and on the radiated noise will be investigated. PCB toroids are compared to standard air-core solenoids and other state-of-the-art air-core toroids both theoretically and experimentally: at first, using ANSOFT Maxwell and ANSOFT Q3D simulation tools, and subsequently, with laboratory measurements (irradiated noise, efficiency, and frequency response) on several prototypes. These very flexible and rather easy to manufacture inductors appear very attractive for compact high-frequency dc-dc converters where high efficiency, low volume, and low noise are of primary concern.

TID and Displacement Damage Effects in Vertical and Lateral Power MOSFETs for Integrated DC-DC Converters

TID and displacement damage effects are studied for vertical and lateral power MOSFETs in five different technologies in view of the development of radiation-tolerant fully integrated DC-DC converters. Investigation is pushed to the very high level of radiation expected for an upgrade to the LHC experiments. TID induces threshold voltage shifts and, in n-channel transistors, source-drain leakage currents. Wide variability in the magnitude of these effects is observed. Displacement damage increases the on-resistance of both vertical and lateral high-voltage transistors. In the latter case, degradation at high particle fluence might lead to a distortion of the output characteristics curve. HBD techniques to limit or eliminate the radiation-induced leakage currents are successfully applied to these high-voltage transistors, but have to be used carefully to avoid consequences on the breakdown voltage.

Optimization of shielded PCB air-core toroids for high efficiency dc-dc converters

The paper describes the design of optimized PCB air-core toroids for high frequency DC-DC converters with strict requirements in terms of volume and noise. The effect of several design parameters on the overall inductor volume, on DC and AC winding resistance, and on the radiated noise will be investigated. PCB toroids are compared to standard air-core solenoids and other state-of-the-art air-core toroids both theoretically and experimentally: at first using ANSOFT Maxwell and ANSOFT Q3D simulation tools, subsequently with laboratory measurements (irradiated noise and efficiency) on several prototypes. These very flexible and rather easy to manufacture inductors appear very attractive for compact high frequency DC-DC converters where high efficiency, low volume and low noise are of primary concern.

Radiation-Induced Short Channel (RISCE) and Narrow Channel (RINCE) Effects in 65 and 130 nm MOSFETs

The behavior of transistors in commercial-grade complementary metal-oxide semiconductor technologies in the 65 and 130 nm nodes has been explored up to a total ionizing dose of 1 Grad. The large dose tolerance of the thin gate oxide is confirmed, but defects in the spacer and STI oxides have a strong effect on the performance of the transistors. A radiation-induced short channel effect is traced to charge trapping in the spacers used for drain engineering, while a radiation-induced narrow channel effect is due to defect generation in the lateral isolation oxide (STI). These strongly degrade the electrical characteristics of short and narrow channel transistors at high doses, and their magnitude depends on the applied bias and temperature during irradiation in a complex way.

Development of custom radiation-tolerant DCDC converter ASICs

Based on a detailed study of the radiation tolerance of high-voltage transistors, 2 commercial CMOS technologies have been selected for the design of synchronous buck DCDC converter ASICs. Three prototype converters have been produced, embedding increasingly sophisticated functions. The electrical and radiation performance of these prototypes is presented.

DC-DC converters with reduced mass for trackers at the HL-LHC

The development at CERN of low noise DC-DC converters for the powering of front-end systems enables the implementation of efficient powering schemes for the physics experiments at the HL-LHC. Recent tests made on the ATLAS short strip tracker modules confirm the full electromagnetic compatibility of the DC-DC converter prototypes with front-end detectors. The integration of the converters in the trackers front-ends needs to address also the material budget constraints. The impact of the DC-DC converters onto the material budget of the ATLAS tracker modules is discussed and mass reduction techniques are explored, leading to a compromise between electromagnetic compatibility and mass. Low mass shield implementations and Aluminum core inductors are proposed. Also, the impact on emitted noise due to a size reduction of critical components is discussed. Finally, material reduction techniques are discussed at the board layout and manufacturing levels.

Optimization of DC-DC Converters for Improved Electromagnetic Compatibility With High Energy Physics Front-End Electronics

The upgrade of the Large Hadron Collider (LHC) experiments at CERN sets new challenges for the powering of the detectors. One of the powering schemes under study is based on DC-DC buck converters mounted on the front-end modules. The hard environmental conditions impose strict restrictions to the converters in terms of low volume, radiation and magnetic field tolerance. Furthermore, the noise emission of the switching converters must not affect the performance of the powered systems. A study of the sources and paths of noise of a synchronous buck converter has been made for identifying the critical parameters to reduce their emissions. As proof of principle, a converter was designed following the PCB layout considerations proposed and then used for powering a silicon strip module prototype for the ATLAS upgrade, in order to evaluate their compatibility.

An 8W-2MHz buck converter with adaptive dead time tolerant to radiation and high magnetic field

A high efficiency 8W-2MHz ASIC buck converter tolerant to radiation and high magnetic field is presented. A new adaptive control circuit for the dead time management is integrated to increase the efficiency during quasi-square wave (QSW) operation. The ASIC is designed in the IHP SGB25GOD 0.25μm technology and developed for the Large Handron Collider (LHC) experiments upgrade, where the main constrains are the presence of a severe radiation environment (up to hundreds of Mrad), a high magnetic field (up to 4 Tesla) and mass limitation because extra material is detrimental to the physics performance of the detector.

Low noise DC to DC converters for the sLHC experiments

The development of front-end systems for the ATLAS tracker at the sLHC is now in progress and the availability of radiation tolerant buck converter ASICs enables the implementation of DC to DC converter based powering schemes. The front-end systems powered in this manner will be exposed to the radiated and conducted noise emitted by the converters. The electromagnetic compatibility between DC to DC converters and ATLAS short strip tracker hybrid prototypes has been studied with specific susceptibility tests. Different DC to DC converter prototypes have been designed following a noise optimization methodology to match the noise requirements of these front-end systems. The DC to DC converter developed in this manner presents a negligible emission of noise that was confirmed by system tests on an ATLAS tracker front-end module prototype. As a result of this, power converters can now be integrated in close vicinity of front-end chips without compromising their overall noise performance.

Power distribution with custom DC-DC converters for SLHC trackers

The upgrade of the LHC experiments at CERN brings new challenges in the design and integration of the detectors. Among them and to achieve the required channel density, the power distribution to the front-end electronics of the trackers has to be implemented in a more efficient and compact manner. This paper proposes a new powering scheme for the trackers based on the use of custom on-board DC-DC converters. The converters are designed to tolerate high levels of radiation and intense magnetic fields present in the experiments.