A high-resolution tail-capacitor based tuning scheme for LC-DCO

This paper presents a high resolution tuning scheme for the LC digitally-controlled-oscillator (DCO) based on desensitized tail capacitance tuning. The sensitivity of the oscillation frequency to the tail capacitance is quantitatively analyzed. The impact of the tail capacitance on the phase noise is qualitatively discussed. Our analysis and simulation results show that both the phase noise and the resolution can be improved simultaneously if the tail capacitance value is properly designed. A 2.4 GHz DCO designed in 65-nm CMOS technology is simulated for demonstration. The tuning resolution can be improved by a factor of 20, and the phase noise at 1 MHz offset can be improved by 2 dB.