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- Stochastic theater: stochastic datapath generation framework for fault-tolerant IoT sensorsPublication . Duarte, Rui Policarpo; Véstias, Mário; Carvalho, Carlos; Casaleiro, JoãoStochastic Computing has emerged as a competitive computing paradigm that produces fast and simple implementations of arithmetic operations, while offering high levels of parallelism, and graceful degradation of the results when in the presence of errors. IoT devices are often operate under limited power and area constraints and subjected to harsh environments, for which, traditional computing paradigms struggle to provide high availability and fault-tolerance. Stochastic Computing is based on the computation of pseudo-random sequences of bits, hence requiring only a single bit per signal, rather than a data-bus. Notwithstanding, we haven’t witnessed its inclusion in custom computing systems. In this direction, this work presents Stochastic Theater, a framework to specify, simulate, and test Stochastic Datapaths to perform computations using stochastic bitstreams targeting IoT systems. In virtue of the granularity of the bitstreams, the bit-level specification of circuits, high-performance characteristics and reconfigurable capabilities, FPGAs were adopted to implement and test such systems. The proposed framework creates Stochastic Machines from a set of user defined arithmetic expressions, and then tests them with the corresponding input values and specific fault injection patterns. Besides the support to create autonomous Stochastic Computing systems, the presented framework also provides generation of stochastic units, being able to produce estimates on performance, resources and power. A demonstration is presented targeting KLT, typical method for data compression in IoT applications.
- True random number generator implemented in 130 nm CMOS nanotechnologyPublication . Monteiro, Pedro; Oliveira, Luís; Casaleiro, JoãoRandom generators systems have the capacity to generate cryptographic keys which, when mixed with the in formation, hide it in an efficient and timely manner. There are two categories of RNG, being truly random (TRNG) or pseudorandom (PRNG). To study the entropy source based on the noise of an oscillator, and to achieve that, an RNG circuit was designed to have a low power consumption, a high randomness and a low cost and area usage. The chosen architecture for this paper is a hybrid RNG, which uses oscillators and a chaotic circuit to generate the random bits. With the simulation of the circuit, it was found to be at the objectives mark, having a low power consumption of 1.19 mW, a high throughput of 25 Mbit/s and an energy per bit of 47.6 pJ/bit. However, due to limitations with the simulation, it wasn’t possible to run all the statistical tests, although all the ran tests were passed.
- A quadrature RC-oscillator with capacitive couplingPublication . Casaleiro, João; Oliveira, Luís B.; Filanovsky, Igor M.In this paper the capacitive coupling in quadrature RC-oscillators is investigated. The capacitive coupling has the advantages of being noiseless with a small area penalty and without increasing the power dissipation. The results show that a phase error below 11 and an amplitude mismatch lower than 1% are obtained with a coupling capacitance about 20% of the oscillator's capacitance value. Due to this kind of coupling, the phase-noise improves by 3 dB (to 115.1 dBc/Hz @ 10 MHz) and the increase of power requirement is only marginal leading to a figure-of-merit of 154.8 dBc/Hz. This is comparable to the best state-of-the-art RC-oscillators, yet the dissipated power is about four times less. We present calculations of frequency, phase error and amplitude mismatch that are validated by simulations. The theory shows that phase error is proportional to the amplitude mismatch, indicating that an automatic phase error minimization based on the amplitude mismatches is possible. The measurements on a 2.4 GHz voltage-controlled quadrature RC-oscillator with capacitive coupling fabricated in 130 nm CMOS circuit prototypes validate the theory.
- Um aparato experimental para estudo e desenvolvimento de circuitos de acondicionamento de sinal: uma experiência pedagógicaPublication . Gomes, M.; Pinto, A.; Fazenda, P.; Casaleiro, JoãoEste documento descreve um aparato experimental desenvolvido pelos autores e relata alguns aspectos da respectiva experiência pedagógica que tem constituído a sua utilização na componente laboratorial de uma disciplina da área da electrónica aplicada. O aparato contém sensores e actuadores incorporados em dois tanques de água e é direcionado para o estudo e teste dos respectivos circuitos de acondicionamento de sinal. A modelação das funções características dos sensores e o desenvolvimento de simples algoritmos de controlo é também exercitado na utilização deste sistema. No contexto académico em que tem sido utilizado, pode encarar-se este sistema como uma reprodução em pequena escala de um hipotético processo industrial, o que tipicamente contribui para uma maior motivação por parte dos alunos e facilita a concepção de enunciados de trabalhos que promovam uma atitude direccionada ao processo como um todo e menos numa soma de tarefas individuais não relacionadas.
- Registador de dados para aplicações de baixo consumoPublication . Casaleiro, João; Rocha, J.; Reis, R.; Pinto, A.; Oliveira, T.; Gomes, M.; Fazenda, P.; Costa, V.; Carvalho, C.Este artigo descreve uma arquitectura de um registador de dados para aplicações de baixo consumo. São apresentados resultados experimentais sobre o desempenho do oscilador, que é um dos módulos do registador. São ainda apresentadas estimativas do consumo do registador e dos respectivos módulos. A autonomia e a estabilidade são os critérios de projecto mais relevantes de um registador de dados para aplicações de baixo consumo que exijam precisão temporal, por exemplo a sismologia oceânica.
- SAR determination and influence of the human head in the radiation of a mobile antenna for two different frequenciesPublication . Pinho, Pedro; Lopes, Amélia; Leite, João; Casaleiro, JoãoThe big proliferation of mobile communication systems has caused an increased concern about the interaction between the human body and the antennas of mobile handsets. In order to study the problem, a multiband antenna was designed, fabricated and measured to operate over two frequency sub bands 900 and 1800 MHz. After that, we simulated the same antenna, but now, in the presence of a human head model to analyze the head's influence. First, the influence of the human head on the radiation efficiency of the antenna has been investigated as a function of the distance between the head and the antenna and with the inclination of the antenna. Furthermore, the relative amount of the electromagnetic power absorbed in the head has been obtained.
- Influence of the human head in the radiation of a mobile antennaPublication . Pinho, Pedro; Casaleiro, JoãoThe big proliferation of mobile communication systems has caused an increased concern about the interaction between the human body and the antennas of mobile handsets. In order to study the problem, a multiband antenna was designed, fabricated and measured to operate over two frequency sub bands 900 and 1800 MHz. After that, we simulated the same antenna, but now, in the presence of a human head model to analyze the head's influence. First, the influence of the human head on the radiation efficiency of the antenna has been investigated as a function of the distance between the head and the antenna and with the inclination of the antenna. Furthermore, the relative amount of the electromagnetic power absorbed in the head has been obtained. In this study the electromagnetic analysis has been performed via FDTD (Finite Difference Time Domain).
- On the feasibility of GPON fiber light energy harvesting for the internet of thingsPublication . Casaleiro, João; Carvalho, Carlos; Fazenda, Pedro; Duarte, R. P.The emerging concept of smart cities demands for a large number of electronic devices, like sensors and actuators, distributed over several public spaces and buildings. The Internet of Things (IoT) has a key role in connecting devices to the Internet. However, the significant number of devices makes the maintenance task of the entire network difficult and expensive. To mitigate this problem, considerable research efforts have been made to develop energy-aware devices capable of self-sustainable operation, by harvesting their energy from various sources. In this paper, we study the possibility of harvesting energy from the light flowing in the Gigabit Passive Optics Network (GPON) to supply low-power devices. Since most cities already have a working GPON installation, using this installation to interconnect and power IoT devices can be a viable and less expensive solution, instead of installing new dedicated networks. This is also an interesting solution to convey communications and energy to low-power applications where access to the power grid is unfeasible. This study is focused in the 1550 nm wavelength, whose available optical power, in residential premises, is between -7 dBm and +2 dBm. With this range of optical power, and with a 30% efficiency photodiode, we show, for the worst-case scenario of the GPON, how it is possible to harvest 62 μW of energy at the Maximum Power Point (MPP).
- Sistema electrónico de controlo de temperatura da água para aplicações domésticasPublication . Oliveira, T.; Reis, R.; Casaleiro, João; Fazenda, P.; Ramos, H.; Pinto, A.; Gomes, M.; Rocha, J.Este artigo descreve um sistema que permite controlar a temperatura e regular o caudal das águas sanitárias num ambiente doméstico. O sistema tem como limite sete saídas independentes de caudal, substituindo as tradicionais torneiras mecânicas e manuais. A arquitectura do sistema está dividida em dois tipos de blocos: a interface com o utilizador (IU) e o bloco de controlo e regulação (CR). A IU é composta por um mostrador e por um teclado que permitem a interacção do utilizador com o sistema. O bloco de CR é constituído por um circuito electrónico que gere os módulos da IU e o sistema electromecânico. No controlo de temperatura é usado um controlador PID digital. A regulação do caudal de cada saída é efectuada de forma independente.