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A digital to time converter with fully digital calibration scheme for ultra-low power ADPLL in 40 nm CMOS
2015-05-27, Wang, Bindi, Liu, Yao-Hong, Harpe, Pieter, Staszewski, Robert Bogdan, et al.
In this paper, a digital-to-time converter (DTC) assisting a time-to-digital converter (TDC) as a fractional phase error detector in an ultra-low power ADPLL is proposed and demonstrated in 40nm CMOS. A phase prediction algorithm via the assistance of the DTC reduces the required TDC range, thus saving substantial power. Additionally, a fully digital calibration algorithm is presented and proved to validate the whole ADPLL system and improve the DTC linearity. At 1 V supply voltage, the measured time resolution of the DTC is 22 ps. The TDC resolution is also indirectly measured with a closed-loop 2.4 GHz ADPLL, where -95.3 dBc/Hz in-band phase noise corresponds to a worst-case TDC resolution of 22 ps.