Tunable Resonators and VCOs for mm-Wave Applications
Cristian Marcu and Ali Niknejad
This research project focuses on the design of high output power CMOS voltage controlled oscillators (VCO) at 60 GHz. Important specifications for VCOs include low phase noise, wide tuning range, and low power consumption. At mm-wave frequencies, these goals are difficult to achieve, and most previously demonstrated VCOs have low tuning range and modest phase noise performance. A key component in oscillators, which can determine both phase noise and tuning range performance, is a high Q tank. At mm-wave frequencies these resonators can take the form of lumped component LC tanks or transmission line resonators. The advantage of transmission line resonators lies in the fact that they support a standing wave at the resonance frequency. This behavior allows for the shaping of the transmission line to reduce losses, and thus increase Q. Previous work has shown the benefits of tapered resonators with certain restrictions. The aim of this work is to explore the fundamental limits of tapering gains that can be achieved.
A number of prototype resonators, shown below, utilize the tapering principle discussed. The protypes are realized in a 90 nm CMOS process. EM simulations were used to derive a model which was then optimized using Matlab to achieve the optimum taper shape. An optimum uniform resonator was also found through simulations and was implemented for comparison purposes. Testing of these prototypes is in progress.
Figure 1: 60 GHz tapered quarter-wavelength resonator