Switched-capacitor controller to control the rise times of on-chip generated high voltages

摘要

A switched capacitor controller accurately controls the rise time of an on-chip generated high voltage. An on-chip charge pump is used to generate a high voltage (VPP) from an external power supply voltage (VCC). This high voltage signal (VPP) can be used to program Flash memory cells. A capacitor of a switched capacitor circuit is selectively switched between ground and a given node voltage. This generates a stair-stepped ramp function. The period of the steps is controlled according to a clock signal. This clock signal may be altered to produce the desired period. The voltage increases of the steps is regulated by a reference voltage multiplied by a ratio between two capacitor values. Thereby, the rise-time of the ramp function is accurately controlled as a function of the frequency of the clock signal and the ratio of the two capacitor values.