A Low Phase Noise Oscillator Principled on Transformer-Coupled

Abstract

Reduced phase noise conversion in a monolithic oscillator suitable for basestation applications is realized by hard limiting and subsequently restoring the resonating waveform. Overdriven transistors hard lim it the drain voltage swing and it is shown analytically that this desensitizes the oscillation phase to circuit noise. A pair of tuned, 1:2 step-up transformers in the feedback path restore the fundame ntal frequency component with sufficient gain to overdrive the transistors forming the oscillator core, with greater selectivity than an equivalent LC tank. The 8 GHz, 65 nm CMOS oscillator prototype targeting the GSM-900 base-station speci fication consumes 32 mA from 1.5 V. Normal- ized to 915 MHz, the phase noise measured at 1 MHz offset is –147.7 dBc/Hz, validating predictions from theory and simulation. The measured frequency pushing is less than 16 MHz/V.