Nanowatt-power-level automatic-switch circuit combining CMOS and photodiode

A nanowatt-power-level automatic-switch circuit that combines an ultralow-power CMOS level converter and a photodiode has been developed as a sensor application. The level converter is a single-input latch-type circuit featuring the use of a depletion-type common-gate MOSFET as a driver transistor, no DC current path, and nanowatt-order power dissipation. To verify the effectiveness of the circuit, a prototype level converter was fabricated on a 0.6-μm CMOS process and used in an automatic-switch circuit in a wireless mouse. The switch circuit is composed of two photodiodes, a current-mirror circuit, the level converter, and a power switch MOSFET. It senses when a hand grabs or releases the mouse and automatically turns the mouse on or off, respectively. The measured power dissipation of the mouse is 3 nW in the standby mode.