Stabilization of phase noise in spin torque nano oscillators by a phase locked loop

TL;DR

This paper demonstrates the reduction of phase noise in spin torque nano-oscillators using a reconfigurable on-chip phase-locked loop, combining experimental analysis and theoretical modeling to optimize noise performance.

Contribution

It introduces a comprehensive theory for STNO locking, including phase slips and 1/f^2 noise, and experimentally validates the effectiveness of a custom PLL in noise reduction.

Findings

Significant phase noise reduction achieved with the PLL

Complex parameter dependencies identified through combined experiment and theory

Provides insights for optimizing STNO noise properties

Abstract

The main limitation in order to exploit spin torque nano-oscillators (STNOs) in various potential applications is their large phase noise. In this work, we demonstrate its efficient reduction by a highly reconfigurable, compact, specifically on-chip designed PLL based on custom integrated circuits. First, we thoroughly study the parameter space of the PLL+STNO system experimentally. Second, we present a theory which describes the locking of a STNO to an external signal in a general sense. In our developed theory, we do not restrict ourselves to the case of a perfect phase locking but also consider phase slips and the corresponding low offset frequency $1/f^2$ noise, so far the main drawback in such systems. Combining experiment and theory allows us to reveal complex parameter dependences of the system's phase noise. The results provide an important step for the optimization of noise properties and thus leverage the exploitation of STNOs in prospective real applications.