Phase Noise and Frequency Accuracy in Crystal-less Wireless Edge Nodes

TL;DR

This paper analyzes how phase noise impacts long-term frequency accuracy in crystal-less wireless edge nodes, introducing N-period-average jitter to improve calibration and evaluate XO-less design feasibility.

Contribution

It introduces N-period-average jitter as a novel link between phase noise spectral characterization and frequency accuracy, enabling better calibration in crystal-less systems.

Findings

Flicker noise dominates long-term frequency accuracy.

The proposed low-cost calibration unit improves frequency precision.

XO-less design feasibility depends on reference noise performance.

Abstract

This paper presents a fundamental analysis connecting phase noise and long-term frequency accuracy of oscillators and explores the possibilities and limitations in crystal-less frequency calibration for wireless edge nodes from a noise-impact perspective. N-period-average jitter (NPAJ) is introduced as a link between the spectral characterization of phase noise and long-term frequency accuracy. It is found that flicker noise or other colored noise profiles coming from the reference in a frequency synthesizer is the dominant noise source affecting long-term frequency accuracy. An average processing unit embedded in an ADPLL is proposed based on the N-period-average jitter concept to enhance frequency accuracy in a Calibrate and Open-loop scenario commonly used in low power radios. With this low-cost block, the frequency calibration accuracy can be directly associated with the reference noise performance. Thus, the feasibility of XO-less design with certain communication standards can be easily evaluated with the proposed theory.