An integrated high efficiency ultra-low power single chip DC/AC inverter for driving liquid crystal electro-optic lenses

An integrated high efficiency, ultra-low power liquid crystal driver for electro-optic diffractive lenses is presented in this paper. The proposed LC driver provides an adjustable 3V to 15V RMS square wave output voltage to drive a liquid crystal in the electro-optic lens, which can be modeled as a 5nF capacitive load. This application is powered by a 3V lithium button cell or energy harvest devices. A reconfigurable hysteretic 2×/3×/4×/5× switched capacitor charge pump is developed for DC-DC conversion to maintain high power efficiency over the entire output power range. An improved H-bridge driving scheme is used to reduce the DC/AC inversion power loss. In addition, an auto-sink scheme is developed to speed up output transaction from high to low in different output modes. Implemented in a 0.25μm 5V V_GS, 12-45V V_DS BCD technology, the proposed LC driver achieves peak power efficiency of 98%. The transaction time of LC driver output from high to low is 48us, which is 219 times faster than that when auto-sink scheme is disabled.