A Crystal-Less Clock Generation Technique for Battery-Free Wireless Systems
Ziyi Chang (Zhejiang University - Hangzhou)
Yunshan Zhang (Zhejiang University - Hangzhou)
Changgui Yang (Zhejiang University - Hangzhou)
Yuxuan Luo (Zhejiang University - Hangzhou)
S. Du (TU Delft - Electronic Instrumentation)
Yong Chen (University of Macau)
Bo Zhao (Zhejiang University - Hangzhou)
More Info
expand_more
Other than for strictly personal use, it is not permitted to download, forward or distribute the text or part of it, without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license such as Creative Commons.
Abstract
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.