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Biasing of Capacitive Micromachined Ultrasonic Transducers
Summary
This study introduces two new high-voltage generator designs to improve capacitive micromachined ultrasonic transducers (CMUTs) for medical imaging. These circuits minimize bias voltage ripple, enhancing signal clarity for better ultrasound diagnostics.
Area of Science:
- Microelectromechanical Systems (MEMS)
- Ultrasound Transducer Technology
- Integrated Circuit Design
Background:
- Capacitive micromachined ultrasonic transducers (CMUTs) offer advantages over piezoelectric transducers for medical ultrasound imaging due to their compatibility with integrated circuits.
- CMUTs require high bias voltage for pulse-echo imaging, but residual ripple from conventional high-voltage (HV) generators can interfere with weak echo signals.
- Minimizing bias supply ripple is crucial for improving the signal-to-noise ratio in CMUT-based ultrasound systems.
Purpose of the Study:
- To analyze existing CMUT biasing circuits and identify their limitations.
- To propose and evaluate two novel HV generator architectures specifically optimized for CMUT biasing.
- To demonstrate the effectiveness of the proposed circuits in reducing bias voltage ripple and improving performance for medical ultrasound applications.
Main Methods:
- Development of an ultralow-residual ripple HV generator utilizing a stable sinusoidal power oscillator.
- Implementation of a second HV generator using a commercial integrated step-up converter with a synchronous capacitor charging approach.
- Integration of the proposed circuits close to the CMUTs within the ultrasound probe (approx. 1.5 cm²).
Main Results:
- The first proposed circuit achieves an ultralow residual ripple (<5 µV).
- The second circuit effectively reduces the impact of switching noise on received echo signals by synchronizing capacitor charging with the pulsing sequence.
- Both novel architectures are shown to be effective for CMUT biasing, with the second being particularly attractive for portable ultrasound devices due to its small size.
Conclusions:
- The proposed novel HV generator architectures significantly improve upon classical CMUT biasing circuits.
- These optimized circuits minimize bias voltage ripple, leading to enhanced performance in medical ultrasound imaging.
- The compact design of the second proposed circuit makes it suitable for integration into portable ultrasound probes, advancing the development of low-cost, high-performance devices.
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