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Publicações

Publicações por Vítor Grade Tavares

2012

Basic analog circuits with a-GIZO thin-film transistors: Modeling and simulation

Autores
Bahubalindruni, G; Tavares, VG; Barquinha, P; Duarte, C; Martins, R; Fortunato, E; De Oliveira, PG;

Publicação
2012 International Conference on Synthesis, Modeling, Analysis and Simulation Methods and Applications to Circuit Design, SMACD 2012

Abstract
This paper addresses a modeling and simulation methodology for analog circuit design with amorphous-GIZO thin-film transistors (TFTs). To reach an effective circuit design flow, with commercially available tools, a TFT model has been first developed with an artificial neural network (ANN). Multilayer perceptron with backpropagation algorithm has been adopted to model the static behavior of the TFT devices, for different aspect ratios. The model was then implemented in Verilog-A, to allow a quick instantiation in circuit. Simulations using Cadence Spectre are performed to validate the model. On a second phase, simulation results of basic analog circuits, with this ANN model, are verified against the actual functional results, namely an adder, subtractor, and current mirror circuit. Results demonstrate not only the ANN model accuracy and compatibility with dc and transient analysis, but also show the a-GIZO TFT capability to perform analog operations. © 2012 IEEE.

2011

Network infrastructure for academic IC CAD environments

Autores
Coke, P; Duarte, C; Cardoso, A; Tavares, VG; De Oliveira, PG;

Publicação
EUROCON 2011 - International Conference on Computer as a Tool - Joint with Conftele 2011

Abstract
This paper presents an initiative to involve ECE undergraduate students in the design and deployment of a network infrastructure for an academic laboratory. The project aims at attaining a reliable and secure network for an IC CAD environment. The students focused on employing secure authentication, accounting and storage with single sign-on, based on enterprise-grade, open-source protocols. This initiative proved to be highly motivating and allowed the students to develop knowledge and hands-on experience on the area of network security. The resulting network design and core infrastructure is herein described as well as its deployment in a real microelectronics design environment. © 2011 IEEE.

2005

Programmable analogue VLSI implementation for asymmetric sigmoid neural activation function and its derivative

Autores
Tabarce, S; Tavares, VG; de Oliveira, PG;

Publicação
ELECTRONICS LETTERS

Abstract
A new CMOS VLSI implementation of an asymmetric programmable sigmoid neural activation function, as well as of its derivative, is presented. It consists of two coupled PMOS and NMOS differential pairs with different programmable bias currents that set the upper and lower limits of the sigmoid. The circuit works in the weak inversion region, for low power consumption and exponential envelope, or in strong inversion to achieve higher speeds. The results obtained from the theoretical transfer function, and from the simulations of the circuit implemented in AMI's 0.35 mu m technology, show a very good match.

2007

Freeman olfactory cortex model: A multiplexed KII network implementation

Autores
Tavares, VG; Tabarce, S; Principe, JC; de Oliveira, PG;

Publicação
ANALOG INTEGRATED CIRCUITS AND SIGNAL PROCESSING

Abstract
This paper presents the results of a CMOS-VLSI implementation of a realistic computational model proposed by Walter Freeman for the olfactory system. This model, in later years, has been studied for engineering applications such as auto-association and classification. The analogue nature of the model motivates analogue VLSI implementations. However, the dimension and complexity of such system poses many obstacles to an analogue electronic implementation; one such is the massive interconnectivity which size increases with the square of the number of inputs (channels). We suggest a multiplexing procedure that puts the burden of interconnectivity over a digital system that is simpler to design and makes the analogue system more treatable. The procedure naturally samples the signals. To avoid smoothing filters, a discrete-time solution was also employed. Although with such approach the time resolution is reduced, the advantages overcome the detriments. Previous work has shown that the model can be efficiently discretized using DSP techniques, resulting on a system that is able to predict, on sample-by-sample basis, the behaviour of the VLSI circuit, allowing for a simple and flexible way to adjust the circuit parameters. We present the measured circuit results that are further confronted with the digital implementation.

2023

Depletion Based Digital and Analogue Circuits with n-Channel IGZO Thin Film Transistors

Autores
Carvalho, G; Pereira, M; Kiazadeh, A; Tavares, VG;

Publicação
2023 IEEE INTERNATIONAL SYMPOSIUM ON CIRCUITS AND SYSTEMS, ISCAS

Abstract
In this work, both analogue and digital depletionmode single channel transistor circuits are presented and are simulated using an n-channel IGZO technology with V-TH =-0.87V. A logic family is introduced, suppressing the need for an additional voltage level and level restoring circuitry. Furthermore, in the analogue domain, a depletion current mirror topology is presented with demonstrated small current error. Finally, the current mirror is used in the design of an OpAmp, achieving a simulated open-loop gain of 45 dB, CMRR of 58 dB, unity-gain frequency of 444 kHz and a phase margin of 71 degrees.

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