A Fully-Synthesizable Fractional-N Injection-Locked PLL for Digital Clocking with Triangle/Sawtooth Spread-Spectrum Modulation Capability in 5-nm CMOS

A fully synthesizable injection-locked phase-locked loop (IL-PLL) for digital clocking is proposed in this letter. The phase-locked loop (PLL) is implemented in a 5-nm CMOS process, with only digital standard cells are used. With proposed triple-path operation and digital offset control for digital-to-time converter (DTC), low-jitter fractional-N frequency synthesis, and highly-linear spread-spectrum clocking are realized with low-power consumption. The PLL core area is 0.0036 mm ² . With 100-MHz reference frequency, better than -234.7 dB figure-of-merit (FOM) is achieved in the fractional-N mode, with -44.3 dBc worst-case fractional spur. The proposed PLL has the smallest chip area, highest FOM, and lowest fractional spur among ring oscillator (RO)-based fractional-N PLLs in sub-20-nm processes.