CMOS Charge pump free of parasitic injection

Claim 1

A substrate bias generator comprising: a semiconductor substrate; a first semiconductor region of a first conductivity type existing in said semiconductor substrate, said semiconductor region supplied with a first potential; a capacitive element formed in said first semiconductor region, said capacitive element including a second semiconductor region as a first electrode and a conductive means formed on said second semiconductor region as a second electrode with an insulation film interposed therebetween; a MOS transistor formed in said first semiconductor region serving as a first rectifying element, said MOS transistor including source and drain regions of a second conductivity type so as to establish a PN junction between said semiconductor region and said source and drain regions, said MOS transistor further including a gate electrode formed on said first semiconductor region between said source and drain regions with an insulation film interposed therebetween; a second rectifying element formed in said first semiconductor region having first and second terminals, said first terminal supplied with a second potential; a third semiconductor region of the second conductivity type existing in said semiconductor substrate, in which circuit elements are formed; voltage supply means for supplying an AC voltage to one of said first and second electrodes of said capacitive element; first means for connecting together the other one of said first and second electrodes of said capacitive element, said gate electrode of said MOS transistor, one of said source and drain regions of said MOS transistor, and said second terminal of said rectifying element; second means for connecting said third semiconductor region to the other one of said source and drain regions of said MOS transistor, whereby said PN junction formed between said first semiconductor region and said source and drain regions is reversebiased during operation of said substrate bias generator.