A 1V fractional-N PLL with nonlinearity-insensitive modulator

A 1V fractional-N PLL is proposed in 40nm technology. With modified VCO, it can be operated under 1V supply with wide tuning range and low supply sensitivity. Besides, conventional 3rd MASH SDM is sensitive to nonlinearity caused by analog path, generating in-band fractional spur that cannot be filtered by PLL loop. In order to lower the sensitivity to nonlinearity, a new type of modulator is proposed. Theorem derivation and simulation results show that this modulator is insensitive to 2nd-5th order nonlinearity. The measured in-band worst-case fractional and reference spur are -64.5dBc and -81dBc, respectively. The RMS jitter is 3.91ps under 5.85mW power consumption.