PhD Defence by Christian Westmark Sønnichsen

Abstract

Modern hearing instruments are complex systems with several microphones, signal processors, wireless radio systems, speakers, and advanced digital signal processors. They implement features such as high-fidelity audio streaming via Bluetooth, artificial intelligence to provide seamless user interaction, directional microphones to improve speech intelligibility in high-noise environments and binaural audio processing to give the user a better listening experience. These features require power, which often is supplied by a rechargeable battery.

Rechargeable batteries can deliver higher output power than disposable batteries, and advances in battery technology has improved the energy density enough to power a hearing aid for a full day’s use, despite strict size-limitations imposed by the stigma often associated with hearing instruments.

To support the continuous miniaturization trend within hearing instruments, rechargeable battery technology, and the increasing need for advanced features, this research has investigated a power management strategy based on a System-on-Chip philosophy. Instead of having a dedicated power management chip, the power management circuit is implemented within the hearing instrument’s digital signal processor chip to improve performance and reduce size.

Semiconductor processes suitable for digital signal processors move towards lower voltages, while rechargeable batteries tend towards higher voltages, resulting in a voltage gap. This research addresses this gap and demonstrates a high-voltage compatible power converter implemented in a low-voltage semiconductor technology while achieving a high-power conversion efficiency of 95.1%.

This achievement, alongside the invention of a remarkably fast level-shifter circuit for use with power converters, and system-level power management strategies devised to reduce the power dissipation of the digital sound processor all contribute towards the goal of creating the next generation of hearing instruments, where power efficiency and miniaturization go hand in hand with advanced functionality.

 

Supervisors

• Principal supervisor: Professor Michael A. E. Andersen, DTU Electro, Denmark.
• Co-supervisor: Paul Stephansson, Analog IC Engineer, GN Hearing A/S.

 

Assessment committee

• Professor Per Lynggaard, DTU Electro, Denmark (chair).
• Associate Professor Torsten Lehmann, UNSW Sydney, Australia.
• Associate Professor Filip Tavernier, KU Leuven, Belgium.

 

Master of the ceremony

• Associate Professor Ouyang, DTU Electro