IR-UWB Receiver Front-End for WSN Applications

Abstract

Ultra-wideband (UWB) has emerged as a very promising technology for short-range communication systems. The ultrashort duration of UWB waveforms gives rise to the potential ability to provide high-precision ranging and localization. Accurate distance measurements between sensor nodes used for localization in wireless sensor networks (WSNs) are very attractive for advanced wireless health-care applications. Over the years, several localization methods like received signal strength intensity (RSSI), angle of arrival (AoA) and time based approaches such as time-of-arrival (ToA) and time-difference-of-arrival (TDoA) exist for distance measurement between sensor nodes. The dominant RSSI is simply estimating the node distance by measuring the strength of the received signal. However, precision is too low with this method. ToA ranging approach is simple but require synchronization to give good precision. Clock synchronization between the transceivers is limiting the accuracy of the ToA estimation and hence increases the design challenges of the UWB ranging system. To our best knowledge no high-precision localization solution suitable for in-body tracking is reported.<br> Impulse radio ultra-wideband (IR-UWB) has been an interesting area of research for lowpower short-range applications. Several studies indicate time-of-flight (ToF) measurements combined with the good temporal resolution of IR-UWB can give good precision. Typical distances between sensor nodes are in the order of ten meters that requires distance measurement is approximately one centimeter. Since radio waves propagate with approximately the speed of light, the time differences of less than 30 ps are required. With traditional clock driven circuit solutions, we need a clock rate of more than 30 GHz, which is not easy in standard technology. Using the new circuit solutions that are still in digital value but continuous in time (Continuous-Time Binary Value–CTBV), it is possible to find effective solutions for precise distance measurement in combination with communication, all are integrated on a single chip.<br> The main goal of this thesis is to develop an IR-UWB receiver front-end covering the frequency band of 3–5 GHz for the CTBV ranging system. The front-end consists of an antenna, a low noise amplifier, a band-pass filter, a downconversion quadrature mixer, a low-pass filter, a differential-to-single-ended converter and a continuous-time quantizer. These building blocks are assembled with other circuit elements of a functional impulse-based radio chip that is demonstrated at short distances. To reduce complexity and to minimize the power consumption, the proposed IR-UWB receiver front-end has been implemented as an energy threshold detector. The quantizer with tunable threshold acts as a single-bit ADC is implemented as a demodulation function. By avoiding using external components as well as high frequency sampling clock, the IR-UWB receiver front-end consumes less power and fully integrated is possible. The proposed IR-UWB receiver front-end is suitable for high-precision low-power low data-rate communication over a relative short range for WSN applications such as ranging and localization.