An integrated 12-V electret earphone driver with symmetric Cockcroft-Walton pumping topology for in-ear hearing aids

Electret-type earphone exhibits a great potential on in-ear hearing-aid applications for the low driving power requirement. However, to enable a static force for thin film's vibration, the input voltage swing has to be large. Instead of using HV technology, in this work we develop a 12-V bridge-type audio driving system by a standard 1.8-V 0.18-μm CMOS. The system integrates two switched-capacitor voltage multipliers, asynchronous regulation loops, and switching-type high-voltage drivers. The proposed symmetric Cockcroft-Walton topology can use MOS thin gate as charging capacitors to save 50% on-chip capacitor area. With differential 12-V output, the maximum output driving current is above 400μA. The peak sound pressure for single audio channel is above 80dß with the open-loop THD+N better than 0.6%.