Infoscience

Thesis

Design of a Discrete-Component Impulse-Radio Ultra Wide-Band (IR-UWB) Testbed and Design of a very Low-Power IR-UWB Transmitter in CMOS Technology

This work presents, in a first part, a testbed for Impulse-Radio Ultra-Wideband (IR-UWB) communication for validating the possibility to do such radio communications. The UWB radio is a radio technique that consists to send extremely short impulses (few nano-seconds) which have a rich spectral content over several hundreds of MHz. The UWB radio we consider here works in the 4.0 to 4.5 GHz frequency range. The IR-UWB radio allows high datarates and small power consumption. In addition, it allows localising precisely a mobile transmitter because UWB signal are similar to those of radar. As UWB radio is different than conventional narrow-band radio, the algorithms used for communication and synchronisation between UWB devices need to be reconsidered. The UWB testbed presented here allows validating and experimenting these algorithms in order to improve and publish them with significant results. There are several already published UWB testbed but few of them are described with enough details to be rebuilt as they are by other researchers or scientists in order to reproduce an experiment. In addition, building such a testbed requires an advanced knowledge not only in electronics and microwave theory but also on practical aspects of building such devices. However, many researchers have not this knowledge because they work on another field and thus, we provide a detailed description about the design and construction of the parts of the testbed in order to help anyone who wants to build the testbed. It is also possible to modify the design of the testbed in order that it works in another frequency range by following the methodology of design we used. The testbed is entirely designed with off-the-shelf discrete components and can be built at a relatively low price. We begin our work by presenting first a very simple but viable UWB testbed in order to understand the principles of UWB radio and to justify further design consideration made later in the work. We also present a mathematical study of UWB signals that allows to rapidly determine their specifications in order to generate a true well shaped UWB signal. This work presents, in a second part, the design and construction of an integrated low-power UWB transmitter in CMOS 0.18um technology. As UWB radio is by nature low-power, we present a novel architecture for generating an arbitrary signal by consuming the smaller as possible amount of energy. We use this architecture for generating the UWB impulse that we determined mathematically in order to have a shape that optimize the spread of energy in the available frequency range (4.0 to 4.5 GHz as for the testbed). We present three prototypes of the architecture where one is patented.

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