First Codesign of 70%-Bandwidth PMUT Array with ±5V Multi-level CMOS Transmitter for Human Artery Ultrasound Imaging in Wearable Devices

This paper presents the first co-designed 64-channel broadband PMUT (piezoelectric micromachined ultrasonic transducer) array integrated with a multi-level CMOS transmitter (TxCMOS) for wearable human artery ultrasound imaging. The system achieves a 70% bandwidth at 5 MHz and is driven by ±5V voltage, offering high performance and low power consumption suitable for non-invasive cardiovascular monitoring.

Key Contributions:

1. Broadband PMUT Array and Multi-Level CMOS Transmitter:

• The 64-channel PMUT array is designed with multi-size PMUT elements to enhance the frequency response, achieving a 70% bandwidth. The multi-level CMOS transmitter enables precise control of the drive voltage and pulse shaping, which is essential for the high transmit and receive efficiency required for wearable applications.

• The system features an 8.4 kPa/V/mm² transmit efficiency and 1.2 mV/V self-reception sensitivity, achieved with a low-voltage drive (±5V).

2. Integration with CMOS Low-Noise Amplifier (LNA):

• Integration of the LNA at the output of the PMUT array boosts the received signal to 60 mVpp, providing a 6x voltage gain, which enhances the signal-to-noise ratio (SNR) for accurate pulse echo measurements.

3. Human Artery Imaging:

• The system was demonstrated for the first time in vivo to capture M-mode ultrasound imaging of the brachial artery, with a 5 mm diameter at 15 mm depth. This imaging achieved 19 µm resolution in simultaneous upper and lower arterial wall tracking, enabling cardiac-cycle-correlated blood pressure calculation.

• The deep tissue imaging capability (15 mm depth) and high resolution (19 µm) are crucial for real-time monitoring of arterial dynamics and blood pressure variations during cardiac cycles.

4. Experimental Results:

• The PMUT array with 4-level pulsing was characterized underwater, showing high efficiency with pulse-echo tests and confirming the system’s broadband capability.

• The system was also evaluated for its pulse echo signal, achieving 70% bandwidth and 11 mVpp received signals at 6.5 mm depth.

• With the LNA, the system achieved significantly improved received signals, demonstrating its suitability for wearable devices.

5. System Integration and Performance:

• The TxCMOS-PMUT platform was compared to state-of-the-art systems, showcasing superior performance with a 15 mm depth capability, high resolution, and low power consumption for continuous physiological monitoring.

Conclusion:
The co-designed TxCMOS-PMUT system successfully integrates a high-bandwidth PMUT array with a multi-level CMOS transmitter for wearable, non-invasive cardiovascular monitoring. This system is capable of high-resolution deep-tissue imaging and accurate blood pressure monitoring, providing a scalable solution for future healthcare applications. Future developments will focus on full SoC integration and AI-accelerated imaging algorithms for continuous monitoring.