Non-integer multi-stage negative charge pump with low area and high efficiency

Abstract

A multi-stage negative charge pump, method and circuit. The circuit includes an input supplying a charge-pump reference voltage (VDDW) to the negative charge pump. A plurality of stages is connected in sequence and an output of a last stage provides a negative charge pump output voltage. Each stage, except the last stage, adds negative VDDW, and the last stage adds a negative fraction of VDDW. An oscillator clock drives each stage, except the last stage. A modulated oscillator clock drives the last stage by a repeating cycle of a modulated oscillator clock, which oscillates during a first time, and stops oscillating during a second time, to generate the negative fraction of VDDW. Durations of the first and second times are defined by an output voltage from a comparator comparing a reference voltage to a voltage from a voltage divider dividing a difference between the output voltage and an LDO voltage.