This article introduces a low-jitter low-spur fractional-N phase-locked loop (PLL) adopting a new concept of a time-mode arithmetic unit (TAU) for phase error extraction. The TAU is a time-signal processor that calculates the weighted sum of input time offsets. It processes two inputs—the period of a digitally controlled oscillator (DCO) and the instantaneous time offset between the DCO and reference clock edges—and then extracts the DCO phase error by calculating their weighted sum. The prototype, implemented in 40-nm CMOS, achieves 182-fs rms jitter with 3.5-mW power consumption. In a near-integer channel, it shows the worst fractional spur below <inline-formula> <tex-math notation="LaTeX">$-$</tex-math> </inline-formula>59 dBc. Under considerable supply or temperature variations, the worst spur still remains below <inline-formula> <tex-math notation="LaTeX">$-$</tex-math> </inline-formula>51.7 dBc without any background calibration tracking.
- Digital-to-time converter (DTC)
- fractional spur
- Phase locked loops
- phase-locked loop (PLL)
- process voltage and temperature (PVT)
- time-mode arithmetic unit (TAU)