A Crystal-Less Clock Generation Technique for Battery-Free Wireless Systems

Ziyi Chang, Yunshan Zhang, Changgui Yang, Yuxuan Luo, Sijun Du, Yong Chen, Bo Zhao

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The size of wireless systems is required to be reduced in many applications, such as ultra-low-power sensor nodes and wearable/implantable devices, where battery and crystal are the two main bottlenecks in system miniaturization. In recent years, battery-free radios based on wireless power transfer (WPT) have shown great potential in miniature wireless systems, while a reliable on-chip clock without a crystal remains a design challenge. Conventional methods utilized the RF WPT tone as the reference for clock generation, but the high RF frequency leads to high power consumption. In comparison, using a lower WPT frequency results in an antenna with a larger size. In this work, the 2nd-order inter-modulation (IM2) component of the two RF WPT tones is extracted to lock an on-chip oscillator, providing a low-jitter PVT-robust clock. In this way, the wireless systems can benefit from: 1) The clock recovery circuits operate at a low IM2 frequency, reducing the power consumption. 2) The WPT can be set to a high RF frequency to minimize the antenna. Fabricated in 65 nm CMOS process, the proposed crystal-less clock generator takes a small area of 0.023 mm2 in a wireless system chip. Measured results show -92 dBc/Hz@10 kHz phase noise and 6.8 μ W power.

Original languageEnglish
Pages (from-to)4981-4992
Number of pages12
JournalIEEE Transactions on Circuits and Systems I: Regular Papers
Issue number12
Publication statusPublished - 2022

Bibliographical note

Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care
Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.


  • Antennas
  • Battery-free
  • clock generator
  • Clocks
  • Crystals
  • Generators
  • injection locking
  • inter-modulation
  • Radio frequency
  • System-on-chip
  • Wireless communication
  • wireless power transfer (WPT)


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