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Open Access Publications from the University of California

Scholarly Works (3 results)

  • Thesis
  • Peer Reviewed
UC Davis Electronic Theses and Dissertations (2022)

Remote vital sign detection has gained popular interests from researchers to conduct through-clothing and non-contact measurements of the chest wall motion induced by the heart beat and the respiration of the human subjects. Although many architectures have achieved the vital sign detection with decent sensitivity, the Doppler radar system is widely adopted by researchers due to its simple architecture, perfect phase coherence and its cost effectiveness. On the other hand, improvements on the Doppler radar system are imperatively needed on the topics of radar system sensitivity for increased detection robustness, spatial resolution for multi-subject detection and linear displacement demodulation. This dissertation is devoted to improve the Doppler radar system through comprehensive study on the coupling effect during the Doppler radar system.

In this dissertation, we first discussed the development on the system integration of a dual-PLL low-IF Doppler radar system using PLL with a shared input reference. Followed by this, a compact module design has been achieved for constructing the first 6x6 Doppler MIMO radar system. This Doppler MIMO radar has been measured with a detection angle accuracy within 1.5 degrees, which helps to accurately allocate the motion-sensitive area of the subject to increase the detection sensitivity. The 18-degree spatial resolution enables the device to distinguish between vital sign signals from two different subjects measured at the same distance of 1.9 m away.

Next, we analyzed the coupling effect contributing to the residual phase noise in the dual-PLL low-IF system architecture and validated it through controlled experiments. Followed by this analysis, an integrated automatic RF cancellation module has been developed using microcontrollers along with the designed cancellation algorithm. This module has been tested under both in-air and through-wall vital sign detection scenarios, resulting in an effective SNR increase of more than 15 dB with a less-than 2 seconds of implementation time.

Lastly, the coupling effect has been studied on the modulation scheme associated with the remote target motion. Instead of the phase modulation due to the Doppler effect, the coupling effect also results in amplitude modulation at the received waveform. Our work investigated such effect through both theoretical derivations and interpretations in an IQ plot. Based on this finding, a new system architecture has been proposed for remote displacement sensing. The developed new architecture demonstrated a superior performance without using the mixer component, which greatly improves the power utilization efficiency for remote displacement sensing.

    • Article
    • Peer Reviewed
    UC Davis Previously Published Works (2017)
    A new wake-up receiver (WuRx) designed in 0.13 μm CMOS process is hybrid-integrated with a micro-electromechanical system (MEMS) RF resonator. While only consuming 166 nW of power (18.8 nW for the comparator and 147 nW for periphery), the WuRx is capable of detecting RF signals as weak as -60 dBm. In order to achieve this sensitivity, a passive voltage-boosting network comprised of a high quality factor (high-Q) piezoelectric MEMS resonator is utilized, in place of an inductor, to amplify the received voltages applied to a CMOS rectifier. The output of the rectifier is then applied to a low-power comparator used to set a logical bit that indicates when an RF signal has been detected. The trade-offs in designing the voltage boosting network are explained and an equation for the optimum number of rectifier stages is derived.
      Creative Commons 'BY-SA' version 4.0 license
      • Article
      • Peer Reviewed
      UC Davis Previously Published Works (2017)
      A monolithic piezoelectric MEMS-CMOS resonant transformer that can be used in ultra-low-power high-efficiency RF sensing applications is presented for the first time. The MEMS-CMOS resonant transformer is based on a 59 MHz 2-port Aluminum Nitride (AlN) Contour Mode Resonator (CMR) bonded to a 0.18 μm NMOS-based rectifier for voltage boosting and RF-to-DC conversion. The integrated device is fabricated in a foundry-based process by conductive eutectic wafer bonding. To amplify the voltage, the AlN CMR is designed to attain a large quality factor (Q=1150) and a relatively low dielectric capacitance (C0=1.51 pF) in relation to the number of rectifier stages (n=20). As a result, a ten-fold voltage gain MEMS-CMOS resonant transformer is demonstrated in this work.
        Creative Commons 'BY-SA' version 4.0 license
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