On the selection of on-chip inductors for the optimal VCO design

The selection of on-chip inductors is crucial to the design of low phase noise voltage controlled oscillators (VCO's). In this paper, we study the effect of substrate on the inductor selection criterion for the VCO circuit and resolve the long lasting argument among circuit designers about whether large or small inductors should be used to reduce the phase noise of VCO's. Several substrate types including CMOS, SOI, and substrates with patterned ground shields (PGS's) are compared, and we demonstrate that the substrate resistivity plays a key role in determining the selection criterion of the optimal on-chip inductors for VCO design.