Low voltage charge pump employing distributed charge boosting

Abstract

A charge pump system, including a charge pump and associated distributed clock generation circuitry, is provided for generating high voltages from a low initial voltage in applications such as erasing and programming electrically erasable programmable read only memory (EEPROM) arrays. The charge pump system uses a power supply voltage and a clock and includes a first phase bootstrapping circuit, an inverter, and a second phase bootstrapping circuit, and a two-stage charge pump. The two phase bootstrapping circuits are both responsive to the clock and use a distributed bootstrapping scheme to provide first and second phase clock signals with fixed multiples of the power supply voltage in order to overcome increased effective transistor threshold voltages, increase efficiency, and allow for charge boosting in a limited number of stages. The inverter is connected to the second phase bootstrapping circuit, causing the second phase clock signal to be opposite in phase from the first clock signal. The two-stage charge pump is responsive to the power supply voltage and the first and second phase clocks and uses native transistors that have lower threshold voltages. A high voltage is produced from the two-stage charge pump by alternately adding charge to the power supply voltage in each cycle of the first and second phase clock signals.