Open AccessCrystal‐less oscillator calibration using serial data as frequency reference
Author(s) -
Yang Wendi,
Jiang Hanjun,
Wang Zhihua
Publication year - 2018
Publication title -
electronics letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.375
H-Index - 146
eISSN - 1350-911X
pISSN - 0013-5194
DOI - 10.1049/el.2018.1216
Subject(s) - ring oscillator , calibration , pulse width modulation , crystal oscillator , signal (programming language) , duty cycle , cmos , chip , frequency drift , electronic engineering , materials science , voltage controlled oscillator , computer science , physics , voltage , electrical engineering , optoelectronics , engineering , telecommunications , resonator , quantum mechanics , programming language
A frequency calibration method for a crystal‐less current‐controlled ring oscillator is presented. It uses a serial data signal from another chip as the frequency reference. The proposed calibration circuit is composed of the coarse calibration and the fine calibration circuit. The coarse calibration circuit controls a binary weighted biasing current source array, while the fine calibration circuit generates a pulse‐width‐modulation (PWM) signal to control a switched biasing current source. The duty cycle ratio of the PWM signal is obtained by measuring the frequency ratio error between the oscillator output and the reference signal. An auto‐correlation‐based method is proposed to calculate the frequency ratio error. The 8 MHz ring oscillator in together with the calibration circuit has been fabricated in a 0.13 μm CMOS process. Measured results on 24 chips show that the relative frequency error is reduced to 0.0239% (mean offset + 3 σ ) after calibration. The reported oscillator shows advantages in accuracy, power consumption and chip area.