Pulse-based ultra-wideband transmitters for digital communication

Abstract

Ultra-wideband radio (UWB) is a rapidly developing wireless technology that promises unprecedented data rates for short-range commercial radios, combined with precise locationing and high energy efficiency. These benefits stem from the use of wide bandwidths and impulse signaling, implying high channel capacity and precise time resolution. UWB has been used for military radar and imaging since the 1950's; however, in 2002 the Federal Communications Commission approved the use of the 3.1-10.6GHz band for unlicensed UWB applications. The restriction on transmitted power spectral density in this band is equal to the noise emission limit of household digital electronics. This band is also shared with several existing services, therefore in-band interference is expected and presents a challenge to UWB system design. This thesis covers the aspects of pulse generation and transmitter implementation for pulsed-UWB communication by exploring tradeoffs that can be made in the pulse shaping in order to reduce power consumption in the transmitter electronics. A transmitter has been developed that exploits the exponential properties of a BJT to approximate a Gaussian shape. It generates BPSK modulated pulses at 100Mb/s in one of 14 channels in the 3.1-10.6GHz band, targeting high data rate applications. The transmitter has been fabricated in a 0.18pm SiGe BiCMOS process, and experimental results are presented. A second transmitter has been developed that uses an all-digital architecture.

(cont.) This architecture is made practical by relaxing the RF frequency tolerance, suitable for communication with an energy detection receiver using pulse position modulation. By using an all-digital architecture, energy is consumed only in CV2 switching losses and subthreshold leakage currents, and no RF oscillator or analog bias currents are required. This transmitter has been fabricated in a 90nm digital CMOS process, and demonstrated in a 16.7Mb/s wireless link.