A Sensitive Method to Measure the Integral Nonlinearity of a Digital-to-Time Converter Based on Phase Modulation
This paper describes a fractional-N subsampling PLL in 28nm CMOS. Fractional lock is achieved by using a 10bit digital-to-time converter (DTC) that generates a delayed sampling clock with minimal impact on PLL performance. Background calibration guarantees appropriate DTC gain, reducing spurs. The system achieves -38 dBc of integrated phase noise (280fs RMS jitter) at 10GHz when a worst-case fractional spur of -43 dBc is present. In-band phase noise is at the level of -104 dBc/Hz. The class-B VCO used can be tuned from 9.2 GHz to 12.7 GHz (32%). The total power consumption of the synthesizer, including the VCO, is 13 mW from 0.9V and 1.8V supplies.