Showing papers by "Fernando Silveira published in 2016"

General Top/Bottom-Plate Charge Recycling Technique for Integrated Switched Capacitor DC-DC Converters

Abstract: Energy loss due to top/bottom plate parasitic capacitances is one of the factors determining the efficiency of integrated switched capacitor DC/DC converters. This loss is particularly significant when MOS gate or deep trench capacitors are used. We propose a technique for top/bottom-plate charge recycling that can be applied with low overhead independently of the converter architecture. Two examples of application of the technique are presented. First, it is shown how the technique can be applied to any converter by transforming it to an interleaved implementation. This approach is demonstrated in a series-parallel 1/3 down converter achieving a maximum load power of 240 $\mu\text{W}$ . Simulation results show an improvement of 7% in the efficiency by decreasing the top/bottom-plate parasitic capacitance losses by 52%. The second example considers an architecture where the proposed technique can be directly applied without additional transformations of the converter implementation. It is a ring modular architecture converter, which was fabricated in a 130 nm CMOS process. An efficiency improvement of up to 4% was achieved in measurements by reducing the top/bottom plate losses by 70%, thus reaching an outstanding efficiency of 80.6% at a conversion ratio of 2/3 and a maximum load power of 2.2 mW.

Bidirectional Analysis and Design of RFID Using an Additional Resonant Coil to Enhance Read Range

Abstract: A recently proposed technique for enhancing near field, wireless energy transfer is to add resonant coils between the transmitter and the receiver. It also has the potential to provide a simple method for enhancing read range of near field radio frequency identification (RFID) systems. In spite of this, its application to the RFID context has not been, yet, deeply analyzed. This paper models and analyzes a half-duplex, frequency shift keying RFID system with one additional coil between the reader and the tag, considering both phases (charging and reading) of this bidirectional operation. A three-coil RFID system was designed using a commercial tag (RI-INL-R9QM widely used in cattle identification), reader (using a TMS3705), and the additional resonant coil (whose radius and quality factor were optimized). In addition, the influence of high coil quality factor is addressed for steady-state and transient response. The designed system increases almost $2.7 \times $ the original RFID read distance (from 16 to 43 cm). The analytical design and measurements data are in good agreement. The design procedure can be applied not only to other RFID systems but also to other systems that use the same channel to energize and transfer data, such as some implantable medical devices.

Central blood pressure monitoring method oriented to wearable devices

Abstract: Arterial hypertension affects a quarter of the world’s population and is a major risk factor for cardiovascular disease. Blood pressure (BP) is one of the most relevant parameters used for continual monitoring of possible hypertension states in the elderly population. Furthermore, emerging evidence suggests that central blood pressure is a more accurate predictor of future cardiovascular events than brachial pressure, thus potentially providing a better hemodynamic determinant for clinical outcomes. This work presents a non-invasive Central (Aortic) blood pressure estimation method based on the pulse transit time (ptt) principle estimated from electrocardiogram (ECG) and ballistocardiogram (BCG) recordings. As the measured transit time presented takes place mainly within the aortic domain, we estimate aortic blood pressure instead of brachial pressure. Validation of the proposed method was performed with a small sample of healthy volunteers at a local gym. An Atcor Medical SphygmoCor device was used to monitor central and brachial blood pressure (systolic, mean, and diastolic) during rests of the strength maneuvers. Pulse transit time was estimated from ECG and BCG recordings and simultaneously recorded with all BP readings. Results showed that Systolic and Mean central blood pressures were most strongly correlated with ppt-estimated blood pressure in comparison to all other blood pressure readings; Bland-Altman plots showed an almost zero mean error (|μ|< 0.02mmHg) and bounded standard deviation σ< 5mmHg for all systolic and mean central BP readings. Experimental data, thus showed promissory results for monitoring aortic blood pressure via ptt. The scope of this pilot work is to provide initial validation of this method in order to develop a compact miniaturized device that allows the integration of wireless blood pressure monitoring into a wearable system.

Uplink wireless transmission overview in bi-directional VLC systems

Abstract: This paper introduces the concept of uplink wireless transmission technologies for visible light communication (VLC). An overview of the different uplink existing methods and its feasibility in various applications such us indoor positioning is presented. We also showed that, unlike existing technologies of wireless communication like, Bluetooth, WiFi and Zigbee, Wireless Power Transfer (WPT) can be not only used for uplink transmission but also provides energy for certain power hungry devices. Simulation results and analytical approximations show that around 450 kbps uplink throughput can be achieved in a system capable of delivering up to 1.3 mW to small indoor devices (94.6×56.8×3.65 mm).

Matching networks for maximum efficiency in two and three coil wireless power transfer systems

Abstract: This work carries out a thorough study of the advantages of using general load matching networks in two and three coil systems. The presented theoretical analysis helps to understand the impact and application of each of the following approaches: adjusting the impedance seen from the load, using additional resonant coils or using both techniques together. A proof of concept system was optimized using a matching network and simulated, showing that the efficiency is improved compared to the case of commonly used resonating structures.

Low-power operational transconductance amplifier with slew-rate enhancement based on non-linear current mirror

Abstract: This paper presents a high slew-rate operational transconductance amplifier (OTA) based on a non-linear current mirror which dramatically reduces the quiescent current. The proposed circuit achieves less quiescent current than previously proposed architectures since no additional bias branches are needed. The compactness of the proposed architecture does not require so much silicon area as other more complex adaptive bias architectures. The proposed technique is compared with previous state of the art high slew-rate architectures. Additionally, this novel architecture was used to design a non-symmetrical OTA which was part of the feedback loop of a switched-capacitor DC---DC converter. This OTA occupies 420 μm2 fabricated in a 130 nm technology. Measurements results are presented showing that a slew-rate enhancement, from 1.5 to 535 mV/μs, is achieved in an OTA biased with 50 nA and loaded with 50 pF.

Modelling approach for low-frequency strongly coupled magnetic resonance wireless power transfer system

Abstract: This work describes the characterization of a three coil system presenting strongly coupled magnetic resonance (SCMR) at low frequency. A theoretical model for the power transmission efficiency between coils is studied, in order to predict the system behaviour, for different positions of the auxiliary coil placed in the middle of the transmission. The best approach for determining each parameter that impacts the performance (inductance, coupling coefficients and quality factor) is found for this low-frequency system. The power transfer efficiency of a typical two coil system is increased 270 times by adding an optimized auxiliary coil in the middle. Theoretical models and experimental measures are in good agreement.

Pushing minimum energy limits by optimal asymmetrical back plane biasing in 28 nm UTBB FD-SOI

Abstract: In this work we propose an optimal back plane biasing (OBB) scheme to be used in a UTBB FD SOI technology that minimizes the energy per operation consumption of sub threshold digital CMOS circuits. By using this OBB biasing scheme, simulations show that around 30% energy savings can be obtained with low threshold voltage (LVT) devices in comparison with classic symmetric back plane biasing (SBB) schemes. Additionally, this OBB scheme allows to adjust the performance of the circuit with very small energy penalties. A very simple and intuitive model, for sub threshold digital CMOS circuits, was developed to justify the benefits obtained by OBB. The results predicted by the model are confirmed with extensive simulation results. Finally, we show that the variability in the energy consumption is improved by using OBB and suggests that new sizing methodologies must be studied to fully benefit from the wide back plane voltage range available in UTBB FD SOI technology for the design of robust energy efficient digital circuits.

Design optimization of a CMOS RF detector

Abstract: A procedure to optimize the design of an RF detector is presented. The optimization enables to minimize the minimum detectable signal (MDS), which is beneficial for maximizing the dynamic range, as it is often desired. The optimization also enables to minimize the bias current consumption. The detector architecture is based on a half-wave MOSFET rectifier and is suitable to implement highly linear envelope detectors. The optimization uses a model based on transistor characteristics extracted from simulations. The model was validated by comparing the predicted MDS to measurements performed at 2 GHz to an RF detector on a 90 nm CMOS process.