Design of Wide Band Transformer-Based Oscillator and Capacitive Coupled Multi-Phase VCO

Abstract

Since globe wireless demand is increasing rapidly, more delicate and functional radio frequency (RF) devices are required. Software defined radio (SDR) has been introduced to address the challenges in this complicated wireless environment, which requires wireless systems to be compatible with various wireless standards and protocols. Voltage control oscillator (VCO) is a critical building block of wireless transceivers. For SDR applications, VCOs are required to have wide tuning range, low noise and low power in order to cover multiple frequency bands. In addition, multi-phase VCOs are often needed to generate multi-phase local oscillation (LO) signals for quadrature transceiver and phase array applications. Two kinds of VCOs are proposed in this thesis for different applications. One is a quad-band transformer based VCO using four inductors and each inductor has its own independent cross-coupled core. The proposed VCO circuit contains two main cores and two auxiliary cores, and all cores are designed to have independent current sources for fully controlling the mutual inductance. This VCO circuit was fabricated in a 0.18 μm SiGe BiCMOS technology. The VCO prototypes cover most of the cellular bands. Also presented is a 0.85 V eight-phase capacitive coupling voltage-controlled oscillator (CCVCO) with enhanced swing for low power supply applications. The CCVCO comprises novel multi-phase generation techniques, and employed not only for eight-phase generation, but also for phase noise reduction. The proposed coupling method applying to an 8-phase VCO design has intrinsic advantage of phase noise reduction comparing to its single-phase VCO counterpart.