CMOS VCOs for frequency synthesis in wireless biotelemetry

Abstract

A new phase noise model was used to optimize a differential ring VCO for minimum power consumption. We compare the phase noise performance of three buffer stages using clamped, symmetric and cross-coupled loads, respectively. We propose a cross-coupled buffer topology that achieves lower phase noise by exploiting symmetry. Measured phase noise for a 1.2mW, 150MHz VCO fabricated in 0.5μm CMOS is -103.9dBc/Hz at 500KHz offset, showing good agreement with the theory.