A study of the low frequency noise (LFN) in reference injected Phase Locked Loops (PLL-RI)

Noise generated in electronic devices greatly affects the performance of communication systems. In oscillators, device baseband noise is up-converted to the RF region as phase noise. This work studies important features of the injection locked Synchronous Oscillator (SO), with a focus on its phase noise performance. The SO is incorporated into a modified Phase-Locked Loop (PLL) as a Reference Injected PLL (PLL-RI) which provides improved locking behavior, suppressed low frequency phase noise, and coherency across the tracking range for a constant group delay. The relationship between device baseband noise and oscillators phase noise is developed and noise shaping functions are introduced to describe the suppression of phase noise in PLL-RIs. The analysis is verified by the PLL-RI fabricated in 130nm CMOS technology. Measurement results show the PLL-RI could successfully suppress the phase noise and jitter peaking: 3.1dB and 26dB noise reductions are observed at 1MHz and 10MHz offset from 1GHz carrier frequency respectively compared to the conventional PLL.