A dual-path subsampling PLL with ring VCO phase noise suppression

Abstract

This article presents a 2-GHz dual-path subsampling phase-locked loop (SSPLL) with ring voltage-controlled oscillator (VCO) phase noise suppression (PNS). In addition to the conventional subsampling charge pump (SSCP), a high pass path from the subsampling phase detector (SSPD) to the low-pass filter (LPF) is implemented in the proposed SSPLL. Due to this dual-path architecture, a new in-band zero and pole are introduced into the open-loop transfer function (zero frequency is smaller than the pole frequency), which extends the open-loop unit-gain bandwidth without sacrificing the phase margin. Consequently, the phase noise contribution of the ring VCO is suppressed while the loop stability is ensured. Meanwhile, the phase noise contribution of the high-pass path is negligible compared to the reference and ring VCO’s contribution. Measurement results show that the SSPLL’s closed-loop bandwidth is extended to around 6 MHz with a reference of 20 MHz and the jitter is reduced by 1.34× (from 3.52 to 2.63 ps) with a maximum noise suppression of 6.5 dB at the 1.1-MHz offset. The PNS path consumes 0.16 mW and no delay line or calibration is needed, which results in a relatively high FoMPNC value of 40.5 dB.