Process variation tolerant LC-VCO dedicated to ultra-low power biomedical RF circuits

In this paper, a technique to mitigate the effect of process variations on the performances of a 1.830 GHz nano-scale CMOS LC-VCO is presented. The proposed complementary cross coupled LC-VCO, dedicated to low-power implantable RF microsystems, uses a linear voltage regulator to allow adaptive scaling of the VCO supply as a function of process parameters. The proposed VCO implementation has improved immunity to variations in phase noise and supply current caused by process variations, and hence avoids worst-case design. The LC-VCO was implemented using STMicroelectronics 1-V 90-nm CMOS process and simulated using SpectreRF to validate its performance. Compared with a identical LC-VCO powered using a fixed supply voltage, the average close-in phase noise is reduced by about 3.6-dB at 10 kHz offset, and the 3-¿ deviation is reduced from 3.53 dB to 0.48 dB at the same frequency offset. Furthermore, the average power consumption is reduced by about 40%, as is the 3-¿ deviation in current drawn.