Abstract
Excessive dead time in complementary switches causes significant energy losses in DC-DC power conversion. The optimization of dead time prevents the degradation of overall efficiency by minimizing the body diode conduction of power switches and, as a consequence, also reduces reverse recovery losses. The present work aims at analyzing the influence of one of the most important characteristics of a digital controller, the timer resolution, in the context of dead-time optimization for synchronous buck converters. In specific, the analysis quantifies the efficiency dependency on the timer resolution, in a parameter set that comprises duty-cycle and dead-time, and also converter frequency and analog-to-digital converter accuracy. Based on a sensorless optimization strategy, the relationship between all these limiting factors is described, such as the number of bits of timer and analog-to-digital converter. To validate our approach experimental results are provided using a 12-to-1.8V DC-DC converter, controlled by low- and high-resolution pulse-width modulation signals generated with an XMC4200 microcontroller from Infineon Technologies. The measured results are consistent with our analysis, which predicts the power efficiency improvements not only with a fixed dead time approach, but also with the increment of timer resolution.

Abstract
In this work we present a study addressing the load modulation for wireless power transfer in underwater applications. A voltage-mode class-D in a series-series resonance topology is analyzed with simplified equations provided to describe the operation of the wireless power system, including the influence of the load on the primary side. The analysis is validated through simulation results provided for a resistive load modulation using component SPICE models, including the characterization of coupling coils in salt water.

Abstract
This paper presents the analysis of switching-current (SC) and switching-resistance (SR) modes of operation in digital power amplifiers (DPAs). Large output power back-off (PBO) generally shifts the DPA from SR to SC operation. Hence, an analytical study is performed to characterize these regimes. A current-mode class-D architecture has been used to implement a DPA in which both operation conditions were examined. Two mechanisms were addressed to study the AM-AM performance of the DPA, namely the knee voltage and the output resistance of the transistor. To evaluate the impact of these parameters in the AM-AM profile, we proposed a simplified transistor model in which both parameters can be defined independently without affecting each other. This allowed us to isolate and determine the effects in the AM-AM distortion, helping to conclude that the output resistance turns out to be the most dominant parameter. The study has been validated using simulations in Spectre RF with three different CMOS process nodes (130, 65, and 45nm).

Abstract

Abstract
In this paper we evaluate the long-term deployment feasibility of a large-scale network of abandoned underwater sensors, where power is provided by autonomous underwater vehicles (AUVs) in periodic visits.

Abstract
In this work we focus on the influence of salt water as the medium between two coupling coils to design a wireless power transfer system. An electrical circuit model and an adequate characterization approach is presented to account for the power losses in the conductive medium. Optimum values for the load and efficiency of the power link are determined. Experimental results are provided to compare the performance of the coupling coils between different coupling mediums (air, fresh and salt water).