Hélio Mendonça

A low-power multi-tanh OTA with very low harmonic distortion

This paper presents a wide input range, low-power operational transconductance amplifier (OTA) in weak inversion. The OTA is implemented with tanh-triplets differential pairs, degenerated by a composite configuration to augment the input linear range, thus reducing further the harmonic distortion. Using MATLAB, the mismatch factor (A) of a typical multi-tanh triplet has been optimised for minimum harmonic distortion. The OTA is designed in UMC 0.13um CMOS technology with 1.2V supply. Simulations show that the input range can be extended to 300 mV, while keeping the HD3 below -80 dB. The average power consumption is 13nW, with an open loop-gain of 76 dB and a unity gain frequency of 250 Hz. The low harmonic distortion OTA can find potential applications in low-power and long time constant filters.

An energy study on IR-UWB transmitter using integration-and-fire modulation

The integrate-and-fire model of a biological neuron is an amplitude to time encoding in the spacing between action potentials (spikes). In principle, this encoding can be used to modulate signals in an Impulse Radio Ultra Wide-Band (IR-UWB) transmitter suitable for Wireless Sensor Networks (WSN). This paper presents a system level study on power efficiency using MATLAB/Simulink to evaluate the required energy for an IR-UWB Transmitter using integrate-and-fire encoding technique. Also, a simple but clear comparison with common systems utilizing Nyquist rate Analog-to-Digital Converters (ADC) is presented. This study has been carried out on a band-limited random Gaussian signal and the results show that IR-IF transmitter consumes roughly seven times less energy than a digital UWB transmitter; moreover, in the proposed architecture the need for power hungry ADC is relaxed.

Design considerations for LTCC based UWB antennas for space applications

This paper presents a planar antenna using low temperature co-fired ceramics (LTCC) substrate for extreme environment applications. An ultra wideband (UWB) elliptical patch antenna was designed and fabricated using an LTCC Ceramtec GC substrate to demonstrate the capabilities of the technology for wideband applications. The simulated results were further validated experimentally. The fabricated antenna provides a peak gain of 5dB over a bandwidth of 4 GHz (3 GHz-7 GHz) with return loss better than -10dB. The radiation pattern is omni-directional in the horizontal plane (θ=900) over the whole frequency range.

Differential gain and phase testing using joint time-frequency analysis

An alternative technique for differential gain and phase testing of video ADCs based on the use of joint time-frequency analysis is presented. This technique can lead to a significant improvement in ADC testing time and in the amount of information provided by these specific tests.

ADC testing using joint time—frequency analysis

Abstract Analog-to-digital converter (ADC) characterization is usually performed using stationary stimuli like sine waves. However, the use of a non-stationary stimulus, besides providing testing conditions closer to those found in real applications, can lead to interesting improvements in ADC testing speed. This kind of signal needs proper processing techniques in order to extract useful information. In this paper we propose the use of joint time–frequency analysis (JTFA) for this purpose. The basic principles of the technique, and how it can be used in ADC testing are presented. In particular, a method for characterising an ADC on its entire bandwidth using a single stimulus is described.

A low power clocked integrated-and-fire modulator for UWB applications

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.

From Boolean algebra to processor architecture and assembly programming in one semester

The paper presents the approach followed at the Faculty of Engineering of the University of Porto, to introduce design automation tools and structured design techniques in the first course on digital system design of our Integrated Master in Electrical and Computer Engineering. Digital Systems Laboratory is an introductory course on digital design, with the classical task of teaching Boolean algebra and combinational and sequential circuit design, using gates, flip-flops and medium complexity components/function blocks like counters and shift-registers. The need to cope with new curriculum requirements and modern digital design demands, motivated an extensive reformulation of the course contents and organization, leading to the introduction of the use of hardware description languages and synthesis tools, in order to implement small systems, of increasingly complex nature, on an FPGA platform. At the same time its coverage was extended to include low-level processor architecture issues, and to teach assembly programming for the MIPS processor. The paper describes how this reformulation was carried out. It presents the course contents and timeline, and discusses the main choices that were made. The paper also describes the laboratory experiments that were developed and discusses some of the challenges and results obtained so far.

Global Localisation Algorithm from a Multiple Hypotheses Set

In this paper, a new fast and computationally light weight methodology is proposed to pinpoint a robot in a structured scenario. The localisation algorithm performs a tracking routine to pinpoint the robots position as it moves in a known map. To perform such tracking routine, it is necessary to know the initial position of the vehicle. This paper briefly describes the tracking routine and presents a solution to pinpoint that initial position in an autonomous way. Experimental results on the performance of the proposed methodology are presented in this paper in two different scenarios: (1) in the Middle Size Soccer Robotic League (MSL), with artificial vision data from an omni directional robot, and (2) in an indoor environment with a Laser Range Finder data from a differential traction robot (called Robot Vigil).