Time domain measurement of phase noise in a spin torque oscillator

TL;DR

This paper presents a method for measuring phase noise in a spin torque oscillator using zero crossings, revealing a thermal-driven $1/f^2$ noise spectrum and demonstrating phase noise reduction via a phase-locked loop.

Contribution

It introduces a novel time domain measurement technique for phase noise in spin torque oscillators and compares it with traditional spectral methods.

Findings

Phase noise spectrum follows a $1/f^2$ trend, indicating thermal fluctuations.

Measured linewidth from phase noise is about 70% of spectrum analyzer results.

Phase-locked loop effectively reduces phase noise within its bandwidth.

Abstract

We measure oscillator phase from the zero crossings of the voltage vs. time waveform of a spin torque nanocontact oscillating in a vortex mode. The power spectrum of the phase noise varies with Fourier frequency $f$ as $1/f^2$, consistent with frequency fluctuations driven by a thermal source. The linewidth implied by phase noise alone is about 70 % of that measured using a spectrum analyzer. A phase-locked loop reduces the phase noise for frequencies within its 3 MHz bandwidth.