Microeletronics and systems
Research lines
HIGH-EFFICIENCY TRANSMITTERS FOR MOBILE COMMUNICATION SYSTEMS
The latest generations of mobile communications systems promise competitive performance with current cable modems in a scenario of complete mobility. However, the current rate of growth of wireless applications has dramatically increased the power consumed by these systems. This brings undesirable consequences for the base stations, whose transmitters are responsible for over 60% of its energy consumption, and also to the user, since the advances in battery technology for portable devices do not follow the same pace. As a result, the transmitter design for mobile systems has been guided by the search for high energy efficiency. This implies practically abandoning the classical linear amplification based on the operation of the transistors in linear classes (A, AB and B) and low power levels. This research line aims to search for new transmitter architectures, capable of keeping the transmitter operating at a high efficiency over a wide output power range, and the digital implementation (FPGAs or ASICs) of baseband linearizers, to exploit the operation of transmitters in high efficiency while meeting the stringent linearity requirements. DEVELOPMENT OF BEHAVIORAL MODELS FOR WIRELESS FUNCTIONAL BLOCKS
In modern wireless communication systems, different functional blocks (ADC, DAC, filters, amplifiers, mixers) act on a signal bearing information, contributing both to perform a predetermined task and to the degradation of the signal over the system. When transmitting, the information modulates an RF carrier in both amplitude and phase, in order to improve spectral efficiency. However, since the envelope can be variable, there must be a tradeoff between linearity and efficiency. Unless a linearization scheme is implemented in the transmission chain, the power amplifier should operate at low power levels in order to meet the stringent linearity requirements, degrading the energy efficiency. At the reception, the signal goes through consecutive gain stages, frequency translation, filtering and demodulation. The compromise in this case is to get the highest sensitivity and most useful signal robustness to interference with the lowest possible energy consumption. For the computer aided design of modern mobile communication systems, behavioral models that have low computational complexity are required to represent the functional blocks. These models must accurately represent the complex information signals at the input and output. In this context, this research line aims to develop behavioral models of functional blocks for mobile communication systems. RF SWITCHED RECEIVERS FOR MULTISTANDARD SOFTWARE-DEFINED RADIO APPLICATIONS
With the growing demand on wireless communications, a number of standards are issued and updated. There is currently a trend on converging several technologies on mobile sets so that they can operate at those different standards. Among the RF receiver architectures, one that has been particularly studied is Software Radio, which consists on connecting the analog-to-digital converter (ADC) directly to the antenna and perform demodulation completely on digital domain. In spite of its interest, this approach results in costly ADCs and a high power consumption. A viable trade-off is software-defined radio (SDR), where amplifying and frequency conversion are performed in analog domain and a narrower band is digitized. In this context, this research line aims the study of RF receiver architectures which are better suited for SDR, exploiting discrete-time signal processing. Switched circuits are particularly suited for such processing. Works in this research line include behavioral modeling of switched circuits, validating aspects such as frequency plans, filtering strategies, signal conversion and the specification of individual building blocks for different communication standards. |