Phase Noise Reduction in LC VCO's Using an Array of Cross-Coupled Nanoscale MOSFETs and Intelligent Post-fabrication Selection

Low-frequency noise, thermal noise, and dc characteristics of nanoscale MOS transistors with dimensions close to the process minimum are highly variable. This article demonstrates a phase noise (PN) reduction technique for LC voltage-controlled oscillators (VCOs) that use an intelligent post-fabrication selection of a subset of an array of near minimum-size cross-coupled transistor pairs with reduced low-frequency noise and thermal noise. Using the technique, the PN of a VCO is lowered from the maximum by 3.5 dB at 600-kHz, 1-MHz, and 3-MHz offsets from a 3.8-GHz carrier. The lowest PN of -122, -129, and -139.5 dBc/Hz at 600-kHz, 1-MHz, and 3-MHz offsets, respectively, from a 3.8-GHz carrier has been measured using the PLL method of the Keysight E5052B Signal Source Analyzer. The VCO prototype was fabricated in a 65-nm CMOS process and dissipates 7 mW of dc power. The maximum figure of merit (FoM), including PN, carrier frequency, and power consumption, is 193 dBc/Hz, and the FoM, including the VCO core area, FoM $_{A}$ , is 209 dBc/Hz.