  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.
