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Publications

Publications by CTM

2015

An Adaptive Signal Processing Framework for PV Power Maximization

Authors
Vidal, AA; Tavares, VG; Principe, JC;

Publication
CIRCUITS SYSTEMS AND SIGNAL PROCESSING

Abstract
This paper discusses the possibility of using adaptive signal processing techniques for maximum power point tracking controllers, in order to extract peak power from individual photovoltaic modules. A new technique grounded on unsupervised Hebbian learning theory (maximum eigenvector of the output power) is presented, which works on-online and is capable of operating without a desired response. Important modifications were made to the generic Hebbian adaptation to accommodate the intrinsic feedback loop between the controller and the plant. Analytic derivation of the new update rule is presented, as well as stability analysis by means of Lyapunov theory. Simulation results showing its effectiveness are presented, as well as experimental results.

2015

Analog Circuits With High-Gain Topologies Using a-GIZO TFTs on Glass

Authors
Bahubalindruni, PG; Silva, B; Tavares, VG; Barquinha, P; Cardoso, N; de Oliveira, PG; Martins, R; Fortunato, E;

Publication
JOURNAL OF DISPLAY TECHNOLOGY

Abstract
This paper presents analog building blocks that find potential applications in display panels. A buffer (source-follower), subtractor, adder, and high-gain amplifier, employing only n-type enhancement amorphous gallium-indium-zinc-oxide thin-film transistors (a-GIZO TFTs), were designed, simulated, fabricated, and characterized. Circuit simulations were carried out using a neural model developed in-house from the measured characteristics of the transistors. The adder-subtractor circuit presents a power consumption of 0.26 mW, and the amplifier presents a gain of 34 dB and a power consumption of 0.576 mW, with a load of 10 M Omega//16 pF. To the authors' knowledge, this is the highest gain reported so far for a single-stage amplifier with a-GIZO TFT technology.

2015

A Low Power Clocked Integrated-and-Fire Modulator for UWB Applications

Authors
Kianpour, I; Hussain, B; Tavares, VG; Mendonca, HS;

Publication
2015 Conference on Design of Circuits and Integrated Systems (DCIS)

Abstract
An integrate-and-fire modulator (IFM) is designed for power scavenging systems like: Wireless Sensor Network (WSN) and Radio Frequency Identification (RFID) sensor tags. The circuit works with a clock in order to be able to be synchronized with microprocessors, which must be used to reconstruct the signal. The modulator is simulated using 130nm CMOS technology and the resulting power consumption is around 14nW at a clock frequency of 10 kHz. The OTA individually dissipates roughly 13nW. Signal reconstruction resulted in a 9.2 ENOB.

2015

Detection of Illegitimate Access to JTAG via Statistical Learning in Chip

Authors
Ren, XL; Tavares, VG; Blanton, RD;

Publication
2015 DESIGN, AUTOMATION & TEST IN EUROPE CONFERENCE & EXHIBITION (DATE)

Abstract
IEEE 1149.1, commonly known as the joint test action group (JTAG), is the standard for the test access port and the boundary-scan architecture. The JTAG is primarily utilized at the time of the integrated circuit (IC) manufacture but also in the field, giving access to internal sub-systems of the IC, or for failure analysis and debugging. Because the JTAG needs to be left intact and operational for use, it inevitably provides a "backdoor" that can be exploited to undermine the security of the chip. Potential attackers can then use the JTAG to dump critical data or reverse engineer IP cores, for example. Since an attacker will use the JTAG differently from a legitimate user, it is possible to detect the difference using machine-learning algorithms. A JTAG protection scheme, SLIC-J, is proposed to monitor user behavior and detect illegitimate accesses to the JTAG. Specifically, JTAG access is characterized using a set of specifically-defined features, and then an on-chip classifier is used to predict whether the user is legitimate or not. To validate the effectiveness of the approach, both legitimate and illegitimate JTAG accesses are simulated using the OpenSPARC T2 benchmark. The results show that the detection accuracy is 99.2%, and the escape rate is 0.8%.

2015

A Fast Spatial Variation Modeling Algorithm for Efficient Test Cost Reduction of Analog/RF Circuits

Authors
Goncalves, H; Li, X; Correia, M; Tavares, V; Carulli, J; Butler, K;

Publication
2015 DESIGN, AUTOMATION & TEST IN EUROPE CONFERENCE & EXHIBITION (DATE)

Abstract
In this paper, we adopt a novel numerical algorithm, referred to as dual augmented Lagrangian method (DALM), for efficient test cost reduction based on spatial variation modeling. The key idea of DALM is to derive the dual formulation of the L-1-regularized least-squares problem posed by Virtual Probe (VP), which can be efficiently solved with substantially lower computational cost than its primal formulation. In addition, a number of unique properties associated with discrete cosine transform (DCT) are exploited to further reduce the computational cost of DALM. Our experimental results of an industrial RF transceiver demonstrate that the proposed DALM solver achieves up to 38 runtime speed-up over the conventional interior-point solver without sacrificing any performance on escape rate and yield loss for test applications.

2015

A Cognitively-Motivated Framework for Partial Face Recognition in Unconstrained Scenarios

Authors
Monteiro, JC; Cardoso, JS;

Publication
SENSORS

Abstract
Humans perform and rely on face recognition routinely and effortlessly throughout their daily lives. Multiple works in recent years have sought to replicate this process in a robust and automatic way. However, it is known that the performance of face recognition algorithms is severely compromised in non-ideal image acquisition scenarios. In an attempt to deal with conditions, such as occlusion and heterogeneous illumination, we propose a new approach motivated by the global precedent hypothesis of the human brain's cognitive mechanisms of perception. An automatic modeling of SIFT keypoint descriptors using a Gaussian mixture model (GMM)-based universal background model method is proposed. A decision is, then, made in an innovative hierarchical sense, with holistic information gaining precedence over a more detailed local analysis. The algorithm was tested on the ORL, ARand Extended Yale B Face databases and presented state-of-the-art performance for a variety of experimental setups.

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