Low-threshold voltage multipliers based on floating-gate charge-pumps

The paper presents a low-threshold voltage multiplier circuit that can be used for harvesting energy from ambient radio-frequency (RF) signals. At the core of the circuit is a charge-pump based on CMOS floating-gate transistor diodes (FGTD) whose threshold voltage can be adjusted using indirect programming. We show that the diodes can achieve threshold voltages less than 50 mV, which is typically less than the conventional Schottky diodes fabricated in an equivalent process. A prototype of a 5-stage charge-pump is fabricated in a standard 0.5-mum CMOS process (V_th = 0.7 V and -0.9 V for nMOS and pMOS transistors respectively). Measurement results validate the functionality of the prototype for multiplying and regulating sub-threshold input signals. Using a 5-stage charge-pump we demonstrate operation at less than 300 mV input signal range with an operating frequency ranging from 1-4 MHz.