A Highly-Integrated Low-Intensity Ultrasound System for Wearable Medical Therapeutic Applications

  • Author / Creator
    Jiang, Xiaoxue
  • Ultrasound therapy has a long history of novel applications in medicine. Compared to high-intensity ultrasound used for tissue heating, low-intensity ultrasound (LIUS) has drawn increasing attention recently due to its ability to induce therapeutic changes without significant biological temperature increase. To enable feasible therapeutic applications, small and light devices are needed. However, current commercially available LIUS devices are bulky and expensive. In this thesis, a battery-powered highly-integrated system is proposed to generate low-intensity therapeutic ultrasound for wearable applications.

    As interfacing with ultrasound transducers generally requires a higher voltage than the battery supply voltage, one challenge of designing the battery-powered highly-integrated LIUS system is to design a DC-DC boost converter with a high output voltage while delivering sufficient output power, and meeting the small size constraint at the same time. Another important block of the LIUS system is the transducer driver. A half-bridge driver is utilized for the proposed LIUS system to drive the ultrasound transducer due to its compact design and the capability of high-speed switching. However, a high-voltage (HV) level shifter is needed for the high-side operation of the half-bridge transducer driver. The performance of the HV level shifter affects the speed, power consumption, and robustness of the half-bridge circuit. Therefore, the design of the high-performance HV level shifter presents another challenge.

    The challenges have been effectively solved in this thesis. Charge pumps (also known as switched-capacitor DC-DC boost converters) with high current drive capability and high power conversion efficiency are proposed to overcome the design challenge of the DC-DC boost converter. Undesired charge transfer, which has a direction opposite to that of the intended current flow, presents a significant source of power loss in charge pumps. The proposed charge pumps utilize charge transfer switches with a complementary branch scheme to significantly reduce undesired charge transfer, thereby improving power conversion efficiency and increasing current drive capability effectively. Additionally, an HV level shifter with short propagation delay and low power consumption is proposed in this thesis to enable the high-performance operation of the half-bridge transducer driver. The proposed HV level shifter achieves high-speed switching and low energy dissipation with the approach of pulse triggering. Additionally, fully symmetrical switching avoids signal skew. Compared with other HV level shifters implemented in the same process, the proposed circuit shows both shorter propagation delay and lower power consumption.

    Based on the proposed charge pumps and half-bridge transducer driver, a proof-of-concept miniaturized LIUS device is designed and developed to generate low-intensity therapeutic ultrasound for wearable applications. The miniaturized LIUS device consists of a battery supply, a custom Application-Specific Integrated Circuit (ASIC), an off-chip digital control block, and a piezoelectric transducer. The ASIC, which integrates the proposed charge pump and transducer driver, is implemented in TSMC's 0.18-µm Bipolar-CMOS-DMOS Gen2 process. The digital control block is used to generate the control signals for the ASIC. The piezoelectric transducer is a customized transducer with a resonance frequency of 1.5 MHz. At this frequency, the proof-of-concept miniaturized LIUS device can generate continuous-wave ultrasound with a therapeutic power intensity of 32 mW/cm2. Pulsed ultrasound can also be obtained at a lower power intensity. To further improve the miniaturized LIUS device, three improvements have been proposed in this thesis and a monolithic-chip solution is obtained. An improved ASIC has been designed in AMS's 0.35-µm HVCMOS process, and simulation results have verified its improved performance.

    Compared to current commercially available LIUS devices, the proposed highly-integrated LIUS system is low-cost, compact, and light-weight, which enables affordable and wearable applications.

  • Subjects / Keywords
  • Graduation date
    Spring 2020
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
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