SUBSTRATE OR BACK BIAS GENERATOR

摘要

A circuit for generating a back bias voltage for use in a semiconductor memory device is disclosed, wherein the back bias voltage is clamped within a desired voltage level. The circuit comprises an oscillator for generating a sequence of square waves having a specified frequency, a buffer adapted to be connected with the output of said oscillator and for buffering the output of said oscillator into the square waves having a level of a source supply voltage, a charge pump circuit for providing a back bias voltage by receiving the output of said buffer, and a clamping circuit adapted to be coupled in parallel between the output of said charge pump circuit and a ground level and for clamping within a specified range the back bias voltage being provided by said charge pump circuit in accordance with variations of said source supply voltage.