High-voltage dc power processing thermal control and packaging techniques

The power processor operates in several modes, delivering up to 100 amperes of regulated electrical power, operating at input voltages to 375 volts with outputs controlled by an integral microprocessor. Several alternative packaging concepts are discussed and evaluated. High-voltage design applications, power stage interconnection and EMI considerations are also discussed. Preliminary thermal analyses were performed and the results presented for each conceptual approach with parametric study results given for the selected concept

A new architecture for high-frequency variable-load inverters

Efficient generation and delivery of high-frequency (HF, 3-30 MHz) power into variable load impedances is difficult, resulting in HF inverter (or power amplifier) systems that are bulky, expensive and inefficient. This paper introduces a new inverter architecture and control approach that directly addresses this challenge, enabling radio-frequency power delivery into widely variable loads while maintaining efficient zero-voltage switching operation. We model the proposed architecture, develop design and control guidelines for it and analyze the range of load admittances over which it can efficiently operate and deliver a specified output power. The opportunities posed by the proposed approach are illustrated through time-domain simulations of an example HF inverter system

Raman scattering in correlated thin films as a probe of chargeless surface states

Several powerful techniques exist to detect topologically protected surface states of weakly-interacting electronic systems. In contrast, surface modes of strongly interacting systems which do not carry electric charge are much harder to detect. We propose resonant light scattering as a means of probing the chargeless surface modes of interacting quantum spin systems, and illustrate its efficacy by a concrete calculation for the 3D hyperhoneycomb Kitaev quantum spin liquid phase. We show that resonant scattering is required to efficiently couple to this model's sublattice polarized surface modes, comprised of emergent Majorana fermions that result from spin fractionalization. We demonstrate that the low-energy response is dominated by the surface contribution for thin films, allowing identification and characterization of emergent topological band structures.Comment: 7 pages, 4 figures; added supplemental materia

Theory of Raman response in three-dimensional Kitaev spin liquids: application to β−\beta- and γ−\gamma-Li2_2IrO3_3 compounds

We calculate the Raman response for the Kitaev spin model on the $\mathcal{H}$-$0$, $\mathcal{H}$-$1$, and $\mathcal{H}$-$\infty$ harmonic honeycomb lattices. We identify several quantitative features in the Raman spectrum that are characteristic of the spin liquid phase. Unlike the dynamical structure factor, which probes both the Majorana spinons and flux excitations that emerge from spin fractionalization, the Raman spectrum in the Kitaev models directly probes a density of states of pairs of fractional, dispersing Majorana spinons. As a consequence, the Raman spectrum in all these models is gapless for sufficiently isotropic couplings, with a low-energy power law that results from the Fermi lines (or points) of the dispersing Majorana spinons. We show that the polarization dependence of the Raman spectrum contains crucial information about the symmetry of the ground state. We also discuss to what extent the features of the Raman response that we find reflect generic properties of the spin liquid phase, and comment on their possible relevance to $\alpha-$, $\beta-$ and $\gamma-$Li$_2$IrO$_3$ compounds.Comment: 19 pages, 10 figures. VERSION 2: Corrected Figure 5 and fixed inconsistencies between A and B chain-labelings. Also- a few typos and two new ref

Resonant Raman scattering theory for Kitaev models and their Majorana fermion boundary modes

We study the inelastic light scattering response in two- (2D) and three-dimensional (3D) Kitaev spin-liquid models with \ms band structures in the symmetry classes BDI and D leading to protected gapless surface modes. We present a detailed calculation of the resonant Raman/Brillouin scattering vertex relevant to iridate and ruthenate compounds whose low-energy physics is believed to be proximate to these spin-liquid phases. In the symmetry class BDI, we find that while the resonant scattering on thin films can detect the gapless boundary modes of spin liquids, the non-resonant processes do not couple to them. For the symmetry class D, however, we find that the coupling between both types of light-scattering processes and the low-energy surface states is strongly suppressed. Additionally, we describe the effect of weak time-reversal symmetry breaking perturbations on the bulk Raman response of these systems.Comment: 23 pages, 20 figures, 4 appendices, 2 ancillary file

Switched-capacitor step-down rectifier for low-voltage power conversion

This paper presents a switched-capacitor rectifier that provides step down voltage conversion from an ac input voltage to a dc output. Coupled with current-drive source, low-loss and high step-down rectification is realized. Implementation in CMOS with appropriate controls results in a design suitable for low-voltage very-high-frequency conversion. Applications include switched-capacitor rectification to convert high-frequency ac to a dc output and, combined with inversion and transformation, to dc-dc converters for low-voltage outputs. A two-step CMOS integrated full-bridge switched-capacitor rectifier is implemented in TSMC 0.25 μm CMOS technology for demonstration purposes. For an operation frequency of 50 MHz and an output voltage of 2.5 V, the peak efficiency of the rectifier is 81% at a power level of 4 W.Interconnect Focus Center (United States. Defense Advanced Research Projects Agency and Semiconductor Research Corporation

An RF-input outphasing power amplifier with RF signal decomposition network

This work presents an outphasing power amplifier that directly amplifies a modulated RF input. The approach eliminates the need for multiple costly IQ modulators and baseband signal component separation found in conventional outphasing power amplifier systems, which have previously required both an RF carrier input and a separate baseband input to synthesize a modulated RF output. A novel RF signal decomposition network enables direct RF-input / RF-output outphasing by directly synthesizing the phase- and amplitude-modulated RF signals that drive the branch PAs from the modulated RF input waveform. The technique is demonstrated at 2.14 GHz in a four-way lossless outphasing amplifier system with transmission-line-based power combiner. The resulting proof-of-concept outphasing power amplifier has a peak CW output power of 95 W, and peak drain efficiency of 72%

Four-Way Microstrip-Based Power Combining for Microwave Outphasing Power Amplifiers

A lossless multi-way outphasing and power combining system for microwave power amplification is presented. The architecture addresses one of the primary drawbacks of Chireix outphasing; namely, the sub-optimal loading conditions for the branch power amplifiers. In the proposed system, four saturated power amplifiers interact through a lossless power combining network to produce nearly resistive load modulation over a 10:1 range of output powers. This work focuses on two microstrip-based power combiner implementations: a hybrid microstrip/discrete implementation using a combination of microstrip transmission line sections with discrete shunt elements, and an all-microstrip implementation incorporating open-circuited radial stubs. We demonstrate and compare these techniques in a 2.14 GHz power amplifier system. With the all-microstrip implementation, the system demonstrates a peak CW drain efficiency of 70% and drain efficiency of over 60% over a 6.5-dB outphasing output power range with a peak power of over 100 W. We demonstrate W-CDMA modulation with 55.6% average modulated efficiency at 14.1 W average output power for a 9.15-dB peak to average power ratio (PAPR) signal. The performance of this all-microstrip system is compared to that of the proposed hybrid microstrip/discrete version and a previously reported implementation in discrete lumped-element form.Massachusetts Institute of Technology. Center for Integrated Circuits and SystemsMassachusetts Institute of Technology. Microsystems Technology Laboratories. GaN Energy Initiativ

Theory and Implementation of RF-Input Outphasing Power Amplification

Conventional outphasing power amplifier systems require both a radio frequency (RF) carrier input and a separate baseband input to synthesize a modulated RF output. This work presents an RF-input/RF-output outphasing power amplifier that directly amplifies a modulated RF input, eliminating the need for multiple costly IQ modulators and baseband signal component separation as in previous outphasing systems. An RF signal decomposition network directly synthesizes the phase- and amplitude-modulated signals used to drive the branch power amplifiers (PAs). With this approach, a modulated RF signal including zero-crossings can be applied to the single RF input port of the outphasing RF amplifier system. The proposed technique is demonstrated at 2.14 GHz in a four-way lossless outphasing amplifier with transmission-line power combiner. The RF decomposition network is implemented using a transmission-line resistance compression network with nonlinear loads designed to provide the necessary amplitude and phase decomposition. The resulting proof-of-concept outphasing power amplifier has a peak CW output power of 93 W, peak drain efficiency of 70%, and performance on par with a previously-demonstrated outphasing and power combining system requiring four IQ modulators and a digital signal component separator