A fully integrated charge pump with double-loop control and differentiator-based transient enhancer for neural stimulation applications

This paper proposes a fully integrated charge pump (CP) with a double-loop control and a differentiator-based transient enhancer (DTE) for high-voltage neural stimulation applications. The double-loop control includes a clock-supply-voltage (V_CLK) modulation loop and a pulse-frequency modulation (PFM) loop. The V_CLK modulation loop regulates the output voltage by adjusting V_CLK while the PFM loop adjusts the operating frequency of the CP in accordance with the load current in order to improve power efficiency. The proposed CP combines the function of output voltage regulation and V_CLK generation into a single unit, leading to significantly reduced circuit complexity. The proposed double-loop control is capable of dealing with different dc current requirements while the proposed DTE suppresses the undershoots and overshoots of the output voltage during load transients. The proposed CP has been simulated using a 0.18-μm triple-well CMOS process and occupies an area of 0.537 mm². The post-layout simulation results show that it can provide a regulated 9-V output voltage from a 3.6-V input voltage with a peak power efficiency of 73.4 % at 2-mA load condition. The Monte-Carlo simulation demonstrates that the overshoot and undershoot of the output voltage are kept below 3 % when undergoing a 2-mA load transient.