B. Allongue

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.

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.

DC-DC converters in 0.35μm CMOS technology

In view of the upgrade of the LHC experiments, we are developing custom DC/DC converters for a more efficient power distribution scheme. A new prototype have been integrated in ASICs in the selected 0.35μm commercial high voltage technology that has been successfully tested for all radiation effects: TID, displacement damage and Single Event Burnout. This converter has been optimized for high efficiency and improved radiation tolerance. Amongst the new features the most relevant are the presence of internal linear regulators, protection circuits with a state-machine and a new pinout for a modified assembly in package in order to reduce conductive losses. This paper illustrates the design of the prototype followed by functional and radiation tests.

System Integration Issues of DC to DC converters in the sLHC Trackers

The upgrade of the trackers at the sLHC experiments requires implementing new powering schemes that will provide an increased power density with reduced losses and material budget. A scheme based on buck and switched capacitors DC to DC converters has been proposed as an optimal solution. The buck converter is based on a power ASIC, connected to a custom made air core inductor. The arrangement of the parts and the board layout of the power module are designed to minimize the emissions of EMI in a compact volume, enabling its integration on the tracker modules and staves. I. POWERING TRACKERS AT THE SLHC Today’s high energy physics experiments at LHC embed large and very sensitive front-end electronics systems that are usually remotely powered through long cables. The innermost region of the experiments, the trackers, are those providing the largest density of channels, that must be powered with the minimal mass of cables and with reduced heat dissipation to avoid complex and massive cooling systems. With the upgrade of the accelerator and its physics experiments already being planned, the detectors will require an increased number of electronic readout channels, which will demand more power. This increase of delivered power should be achieved without the addition of material in the detector volume, because of lack of physical space to run more cables and because material in this volume is detrimental to the physics performance of the detector. A solution to deliver more power without increasing the cable volume and mass relies on the distribution of power through on-detector DC–DC converters. These converters must be capable of reliable operation in high radiation (total ionizing dose of 250 Mrad(SiO2) and neutron fluencies of 2.5×10 15 n/cm 2 , 1 MeV neutron equivalent, based on the simulated environment in the central tracker detector over its projected lifetime) and strong DC magnetic field environment (up to 4 T) of the detector. To be compatible with this harsh environment, the electronic devices need to be designed in specific technologies that have been qualified for the required doses and fluencies. Together with the high degree of miniaturization required, this fact imposes the development of a custom ASIC for the implementation of the power controller and switches in a known, radiation qualified technology [1]. The LHC tracker operates with magnetic fields up to 4 T to bend the particles thus allowing their identification. The DC-DC converters will be exposed to this DC magnetic field. This forbids the use of conventional ferromagnetic cores, since they saturate at flux densities below 3 T. Coreless (aircore) inductors have to be used instead, limiting the accessible values of inductance below 700 nH in order to maintain affordable size and mass [2]. A comparative study indicated that the buck converter is one of the most suitable converter topology for the intended application [3]. Given the range of available coreless inductors, the switching frequency has to be set beyond 1 MHz in order to limit the current ripple. A typical tracker front-end system is made of strip detectors that are bonded to front-end hybrid circuits. These hybrids are fitted with several front-end chips. Several hybrid and detector modules are then mounted together to form a stave [4]. Based on this and on the estimated power requirements of the hybrids, an optimal powering scheme based on DC-DC converters (Figure 1) has been defined [3], that relies on an input voltage bus (10V) distributed along the stave to all the hybrids. Each hybrid circuit would be equipped with one Buck DC/DC converter delivering an intermediate bus voltage (2.5V) that brings the power to each front-end chip with a conversion efficiency of 80%. Each front-end chip would then convert the intermediate voltage down to the levels that it requires (1.2V and 0.9V) through integrated switched capacitors point-of-load DC/DC converters, whose efficiency is expected to be around 95%. Beyond the environmental constrains that are set to this powering scheme, the electromagnetic compatibility between the tracker electronics and the DC-DC converter used to power it is essential. The sLHC tracker powered from DC/DC converters in close proximity of the front-end electronics must be able to achieve levels of performance equivalent to those obtained when using remote, regulated power supplies in the present system. The proximity of switching converters with the strips and front-end ASICs (less than 5 cm) expose the front-end electronics to conducted and radiated couplings that could compromise the tracker performance. The compatibility can be achieved by appropriate design of the converter, Figure 1: Powering topology.