Nonlinear analysis and optimization of a Distributed Voltage Controlled Oscillator for Cognitive Radio

Nonlinear design and optimization of a Distributed Voltage Controlled Oscillator (DVCO) suitable for Cognitive Radio is presented. Harmonic Balance (HB) based optimization techniques have been used to obtain an optimized design of the DVCO aiming at minimizing the output power variation along the frequency band. A prototype has been built showing good agreement with simulation. The measured DVCO has a frequency tuning range from 0.75 GHz to 1.85 GHz, an average dissipation of 59 mW, and an average output power of 5.2 dBm. The average measured phase noise at 1 MHz offset from the carrier across the tuning range is -111.2 dBc/Hz.

I. Introduction

Cognitive Radio (CR) technology has been recently recommended to address the issue of “spectrum overcrowding” arising in wireless transmission, due to coexisting telecommunication standards in overlapping frequency bands. This emerging technology calls for flexible receiver architectures, which should cover a wide frequency range in order to efficiently share wireless resources. High performance voltage controlled oscillators are required to achieve this task [1]. In this work a reverse gain mode distributed voltage controlled oscillator (DVCOs) topology is considered, since it offers wideband tuning capability, low phase noise, and a satisfactory spectral purity with remarkable suppression of higher harmonics [2] which makes them natural candidates for Cognitive Radio applications.