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- Generic model for multi-phase ring oscillatorsPublication . Pereira, Paula C.; Couto-Pinto, Antonio; Oliveira, Luis; Fernandes, Jorge R.We present a generic model for Multiple Phase Ring Oscillators (MPRO) with 2n phases, and derive equations for frequency, phase and phase error under the simplifying approach of injecting the error in a single element. Extensive Monte Carlo simulations, at transistor level, for the four and eight phase circuits, are in accordance with these assumptions. These results are validated by two prototype integrated circuits, implemented in a 130 nm CMOS technology: The first prototype, which is a standalone four phases Ring Oscillator (RO), validates the theoretical analysis concerning the non-linear model main conclusions and, the second prototype, which is an eight phase RO, incorporated as a block of an ISM receiver, validates the generic model for CRO concept.
- Combined organic photovoltaic cells and ultra low power CMOS circuit for indoor light energy harvestingPublication . Batista, Duarte; Oliveira, Luis; Paulino, Nuno; Carvalho, Carlos; Oliveira, João P.; Farinhas, Joana; Charas, Ana; Mendonça Dos Santos, PedroThis paper describes an energy harvesting system composed of an organic photovoltaic cell (OPV) connected to a DC-DC converter, designed in a 130 nm Complementary Metal-Oxide-Semiconductor (CMOS) technology, with a quasi- maximum power point tracking (MPPT) algorithm to maximize the system efficiency, for indoor applications. OPVs are an emerging technology with potential for low cost indoor light energy harvesting. The OPV current-voltage curves (I-V) under an irradiance of solar simulator Oriel Sol 3A, at room temperature, are obtained and an accurate electrical model is derived. The energy harvesting system is subjected to four different indoor light sources: 35 W halogen, 3.5 W LED, 5 W LED, and 7 W LED, positioned at three different heights (0.45 m, 0.26 m, and 0.11 m), to evaluate the potential of the system for indoor applications. The measurements showed maximum efficiencies of 60% for 35 W halogen and 45% for 7 W LED at the highest distance (0.45 m) and between 60% (5 W LED) and 70% (35 W halogen), at the shorter distance (0.11 m). Under irradiation, the integrated CMOS circuit presented a maximum efficiency of 75.76%, which is, to the best of the authors' knowledge, the best reported power management unit (PMU) energy system using organic photovoltaic cells.