A 3.3-GHz 4.6-mW Fractional-N Type-II Hybrid Switched-Capacitor Sampling PLL Using CDAC-Embedded Digital Integral Path with −80-dBc Reference Spur

Abstract

We present a type-II fractional-N hybrid switched-capacitor sampling PLL, using a capacitive digital-to-analog converter (CDAC) as a sampler and an analog adder receiving the digital integrator’s output. To guarantee sufficient CDAC settling time and filter switch-on time, we designed a synchronous timing generator utilizing the multi-modulus divider’s (MMDIV’s) inter-stage clocks. The prototype chip in 65-nm CMOS achieves −80-dBc reference spur, 236-fs integrated RMS jitter, and 4.6-mW power consumption, translating to −246-dB FoM.