Multiphase reference signals have become an indispensable element of modern wire less and wireline systems with applications in image reject receivers, high-spee d clock and data recovery systems for serial links, time-interleaved analog-to-d igital converters (ADCs) and more recently quantizers based on voltage-controlle d oscillators (VCOs). Traditional approaches such as ring oscillators fail to sa tisfy the stringent phase noise requirements of many of these high-performance s ystems. In this research we focus on multiphase generation using coupled LC oscillators in which all blocks operate at the desired frequency of operation. However, usin g coupled LC oscillators entails practical issues. In contrast to ring oscillato rs, these circuits possess multiple modes of oscillation, which makes the exact output frequency somewhat unpredictable. Moreover, most existing coupling scheme s result in an undesired trade-off between phase noise and phase accuracy of the coupled oscillators. Attempts to alleviate this tradeo? either fail to solve the issue of multiple modes of oscillation or are e?ective only at a single frequen cy and thus cannot offer a wide-band solution. The goal of this research is to a ddress the issue of multiple modes in coupled LC oscillators and propose methods and topologies to avoid unwanted modes. Additionally, such techniques can poten tially break the trade-off between phase noise and phase accuracy thus resulting in better phase noise performance.
Integrated Circuits Lab
Center for Integrated Systems
Stanford University