Towards Fully Integrated Switched-Capacitor Power Converters in Hearing Instruments’ Digital Signal Processors

In this project, the path towards fully integrated switched-capacitor (SC) converters cointegrated within the digital signal processing (DSP) chip of hearing instruments (HIs) is explored. The power management system should be compatible with lithium-ion battery voltages and ideally scalable to support future developments related to the DSP process technology nodes. Due to strict volumetric constraints, a system-on-chip (SoC) implementation with a fully integrated SC-based power management system is highly desirable. Compared to current HIs with dedicated power management integrated circuits (PMICs) with high-voltage transistors and discrete external capacitors, this represents a significant size reduction but requires advanced packaging options, capacitor technologies, and higher switching frequencies. The HI platform contains multiple sensitive analog-to-digital microphone channels and sensitive wireless transceivers, raising considerable electromagnetic interference (EMI) concerns. The main results of the project include a low-EMI control technique that virtually eliminates output voltage ripple while reducing the input peak current and the charge redistribution losses. The project includes a 95.1% efficient highly integrated lithium-ion compatible quintuple-output asymmetric SC Ladder converter. This converter, based on 900mV core transistors in a 28nm fully depleted silicon on insulator (FD-SOI) process, demonstrates the feasibility of a lithium-ion HI SoC from a power management perspective. One of the identified challenges when pursuing a fully integrated symmetric Ladder implementation was level shifting synchronized high-frequency gate-control signals above 100MHz to the symmetric Ladder. This led to the invention of a four-transistor FD-SOI-based picosecond delay backgate driven floating high-voltage level shifter circuit which is 74 times faster and has a 2.7 times lower dynamic power dissipation than state of the art for a comparable application, voltage, and process technology. Finally, several subjects including three-dimensional dynamic bias voltage, supply voltage and frequency scaling, dynamic body biasing of power switches, and analysis and characterization of cross-regulation effects present in multiple-output SC DC-DC converters have been studied.