A wideband low-jitter PLL with an optimized Ring-VCO

Abstract

A wideband low-jitter phase-locked loop (PLL) is proposed to provide high performance clocks for the transceivers. The ring voltagecontrolled oscillator (Ring-VCO) is a key component of a PLL, which directly determine the out-band phase noise and output frequency range of the PLL. Therefore, a low phase noise two-stage Ring-VCO with a novel delay cell is proposed to help achieve a wideband low-jitter PLL. An accumulation-mode MOS (AMOS) varactor pair is adopted in the delay cell to improve the fine tuning linearity. Moreover, an additional AMOS varactor pair is employed to reduce the VCO gain variation in the coarse tuning process and enhance the tolerance in temperature and voltage variations. Implemented in a conventional TSMC 180nm CMOS process, the proposed Ring-VCO can tune from 0.73 to 1.92 GHz and the worstcase phase noise at 1MHz offset is -102 dBc/Hz. The output frequency range of the proposed PLL is 0.06-1.92 GHz and the RMS jitter is less than 3.8 ps over the whole working band.