A 6.5-GHz Monolithic CMOS Voltage-Controlled Oscillator

A monolithic CMOS voltage-controlled oscillator (VCO) incorporates two identical fixed-frequency LC oscillators coupled in a ring topology to generate a variable-frequency output by varying the coupling between the two oscillators. Operating from a single 1. 5-V supply and dissipating 18 mW, the core VCO can be tuned between 5.51 and 6.53 GHz without the use of varactor diodes, yielding a tuning range of 1.02 GHz. Fabricated in a 0.35-micron CMOS technology, the 6.29 GHz VCO exhibits -98.5 dBc/Hz phase noise at an offset frequency of 1 MHz.