An Oscillator System for a Quadrature Downconversion Auto-Correlation Ultra-Wideband (UWB) Receiver

Abstract

The fast development of CMOS IC process technology and the opening up of high frequency bands by regulatory bodies has aided wireless communication industry with development and commercialization of long-medium and short range wireless communication applications, for example GSM, Wireless LAN, Bluetooth and UWB. Ultra Wideband (UWB) is a promising technology that covers a bandwidth from 3.1GHz to 10.6GHz, which features distinctive advantages, such as high data rate over short and medium range, low interference or co-existence with other wireless technologies and robustness towards multipath fading and possible usage in personal area network (PAN) and body area network (BAN), targeting especially health care monitoring applications. Impulse radio UWB or ir-UWB, is one of the UWB technologies, which applies transmission of short duration (pico-nano second) and carrier less pulses. Several receiver architectures [1, 2 & 3] based on the principle of correlation has been proposed, with Quadrature Downconversion Auto-Correlation Receiver (QDAcR) [3] being one of them. This thesis work builds up further on the generalized QDAcR model of [3], starting with an advanced time domain analysis of principle of Downconversion in QDAcR and exploring the dependency of QDAcR on downconverter related stochastic perturbations such as phase noise, jitter and amplitude perturbations. The use of Stationary Stochastic Process Theory, Fokker-Planck Equation and Floquet’s Theory resulted in a simplified equation, incorporating the effect of stochastic perturbations; this equation of prominence, further can be extrapolated to perturbation analysis of Zero (low) – IF receivers. A complete system modeling of QDAcR downconverter resulted in vital specifications for the QDAcR downconverter being the requirement of a 5.6 GHz quadrature voltage controlled oscillator (QVCO) with a minimum phase noise of -90dBc/Hz at 1MHz offset and with a maximum permissible phase error of 4 degrees. This relaxed nature of specifications has opened a plethora of trade-offs. The main aim being the design of low power Quadrature oscillator, a push-pull LC tank voltage controlled oscillator, consuming 1mW of power and exhibiting figure of merit of 187.1dB with a tuning range of 12.7% was designed. The Bottom Series QVCO, Parallel Coupled QVCO and Push-Pull –Polyphase QVCOs were compared for their respective advantages and disadvantages, which resulted in the selection of the Parallel Coupled QVCO, because of less power consumption and robust design. The Parallel QVCO consumes a power of 2.4mW, while having a FOM of 186.36dB. The final design includes the complete QVCO system and differential buffer (Common Source) with neutralization capacitors having ability to drive variable loads.