A 10 V Fully-Integrated Switched-Mode Step-up Piezo Drive Stage in <inline-formula> <tex-math notation="LaTeX">$0.13\,\upmu\text{m} $</tex-math> </inline-formula> CMOS Using Nested-Bootstrapped Switch Cells

Abstract

A completely integrated 3.3 V to 10 Vpk-pk bidirectional switched-capacitor ladder converter is presented for driving the piezo actuators of a 2 mm wing micro-robotic flying insect. The 0.1-10 MHz converter, fabricated in 1.2 V/3.3 V triple-well 0.13 μm CMOS, operates as a switched-mode amplifier with 0-3.3 V waveforms at the input and a constant 3× step-up while exhibiting symmetric drive strength for positive and negative load currents. A feedforward switching scheme that effectively bootstraps gate-drive signals for the power switches of the ladder converter has been implemented to enable output waveforms above both the supply and device voltage rating, between 0 V and ~10 V. Nonoverlapping clock signals float with the dc-500 Hz arbitrary input waveform, or a 2× scaled replica, while keeping all transistors within safe operating conditions. A voltage compliant sub-circuit, the Nested-Bootstrapped Switch (NBS) cell, is introduced as a building block for the creation of the gate-drive signals. On-chip MIM capacitors and 3.3 V I/O MOS switches for the ladder converter were sized based on a charge-multiplier representation of the converter and the output impedance concept. Experiments show actuation of a 2 mm wing prototype, an effective 5 nF peak load, and efficiency of 77% at 800 μW and 80% at 32 μW.