Transducer driver with active bootstrap switch

This paper presents a high-voltage driver with both upper-side and lower-side power transistors, which is used to drive a piezoelectric transducer. An active bootstrap switch circuit has been proposed to replace the diode required in a conventional bootstrap circuit. This work is primarily driven by the lack of diodes for high-temperature operation. Besides that, the proposed design has the advantages of smaller in size, robust thermal stability, and low forward voltage drop, compared to the bootstrap diode approach. In addition, the active bootstrap switch circuit mitigates the capacitor over-charge issue due to the negative transient voltage at the output of the driver. The design is fabricated using 1.0-μm SOI CMOS process, and the reverse leakage current of the active bootstrap switch is measured up to 300 °C, beyond the specified process limit of 225 °C.