A 2 GHz 3.1 mW type-I digital ring-based PLL

This paper presents a type-I digital ring-based PLL with wide loop bandwidth to lower the ring oscillator's noise contribution. The in-band noise is addressed using a SAR-ADC-based sampling phase detector (SPD). A stacked reference buffer is also introduced to reduce the transient short-circuit current for low power and low reference spur. The loop delay due to the D flip-flops at filter's output is compensated in order to lower the noise peak, and stably achieve the wide loop bandwidth. The locking issue due to the static phase error in a type-I PLL and the limited range of the PD is addressed using a TDC-assisted loop. The prototype PLL fabricated in 65 nm CMOS demonstrates 2.4 ps RMS jitter, 3.1 mW power consumption, and 0.067 mm2 area, with 50 MHz reference frequency and 2.0 GHz output frequency.

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