Abstract
High voltage pumping circuit is a function block for some special applications like EEPROM, LCD driver, MEMS, and other peripheral interfaces. In this work, the driving circuit is targeted for electrostatic earphone application. In contrast to conventional electromagnetic earphone, electrostatic ones need high voltage input instead of large driving current. These loads can save a lot of system power. However, designing high voltage circuits using standard CMOS process technology is a challenge. In this report, a voltage multiplier and a high voltage driver circuits based on switched capacitor techniques are developed. Two types of voltage multiplier are proposed. To achieve fully integration, minimum area occupation has to be guaranteed. All the voltages cross the transistors and capacitors are carefully evaluated to alleviate the reliability issues. A closed-loop PFM system is constructed to make sure stable output voltage under different loading condition. New voltage division network is proposed in this loop to reduce the power and area overhead. Under the loading current from 100A to 600A, the prototype chip demonstrates the regulated output is 6V when input voltage is 1.2V. The output voltage ripple is 30mV and the closed-loop power efficiency is 8.5%. High voltage driver is used to drive audio PWM pulse to load. A modified structure eliminates the level shifter and high voltage predriver therefore reduces the transient power. Integrated the driver with pumping circuits, the measurement results demonstrate that the output spectrum is around -9dBm which is closed to the theoretical value. The output swing is 5.87V when input pulses are 1.8V. All the prototype circuits are using standard 0.18m CMOS technology.