Abstract
In this work, a special high voltage application, the electret earphone driver, will be presented. Instead of requiring high current, the electret earphone needs to be driven with high voltage swing. Since the characteristic of electrostatic earphone consumes no large current, the charge pump is a good solution to provide high voltage to the driver. To reduce the cost, the high-voltage generator and driver circuit is fully integrated in standard CMOS process technology in this work. Devices in standard CMOS process technology operating with high voltage may cause several reliability problems, such as oxide breakdown and hot carrier effect. In this design, these reliability issues have been well considered. Morover, MOS capacitors are used instead of MIM capacitors to reduce chip area since the unit capacitance of MOS capacitor is greater than MIM capacitor. A new topology of voltage multiplier is proposed which makes the cross voltage of all capacitors less than standard power supply voltage to guarantee the reliability of MOS capacitor. To sustain stable voltage output, a burst mode control regulation loop around the voltage multiplier is implemented. To make system-on-chip possible, all these functions are integrated in a standard CMOS process technology. The proposed regulated voltage multiplier can achieve 6V output voltage under the loading current from 100uA to 350uA. The output swing of the driver is up to 6V and the reliability of all transistors is well concerned. A bridge connected high-voltage driver can drive the electret earphone to almost 80dB sound pressure level.