A 5.8-GHz VCO with Precision Gain Control

In this paper, we present a fully integrated 5.8-GHz LC voltage controlled oscillator (VCO) featuring over 300 MHz tuning range while retaining the VCO gain (K_VCO) to as low as 45 MHz/V A modified frequency-tuning topology employing accumulation-mode MOS varactors (AMOS) with virtual ground node bandswitching was adopted to set the appropriate operating frequency and to program K_VCO to a necessary minimum. Realized in 0.13 mum CMOS technology, the VCO obtains an adjustable gain ranging from 45 MHz/V to 106 MHz/V in 20 MHz/V-step. With mimimum K_VCO, phase noise improves by 6 dB and goes down to -115 dBc/Hz at 1 MHz offset away from 5.98 GHz carrier while dissipating merely 12.5 mW dc power.