Design of Modified Four-Phase CMOS Charge Pumps for Low-Voltage Flash Memories

A new four-phase clock scheme for the four-phase charge pumping circuits using standard 0.5 μm CMOS technology at low supply voltages to generated high boosted voltages is proposed. Boosted clocks without high drivability are applied on the capacitors coupled to the gates of the main charge transfer transistors to compensate body effects. Thus, the high-voltage clock generation circuit can be easily achieved for clock frequency of 10 MHz. Due to the nearly ideal pumping gain per stage, the design methodology to optimize power efficiency is also presented. With the new clock scheme, it can efficiently pump to 9 V at supply voltage of 1 V using 10 stages by simulations, while pump to 4.7 V at supply voltage of 1.5 V using four stages by measurements.

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