Voltage pump circuit having an independent well-bias voltage

Claim 1

A voltage pump circuit comprising: a voltage pumping section having a first MOS transistor coupled between a boosted voltage and a first node, a second MOS transistor coupled between said first node and a first potential voltage, a third MOS transistor coupled between said first potential voltage and a second node, a fourth MOS transistor coupled between said second node and a second potential voltage, and a first pumping capacitor coupled between said first node and said second node, wherein said voltage pumping section generates a reference voltage at said second node by precharging and pumping a charge to and from said first pumping capacitor; a level shifter for receiving an oscillation signal, and for providing shifted signals for gates of said first MOS transistor and said second MOS transistor, respectively, in accordance with a logic level of said oscillation signal; a first non-overlap circuit for receiving said oscillation signal and said shifted signals for generating a charging control signal and a pumping control signal to gates of said third MOS transistor and fourth MOS transistor, respectively; a well-bias voltage generator having a second non-overlap circuit, a second pumping capacitor, a first and second bootstrap capacitor coupled between a precharge circuit and said second non-overlap circuit, a first step control circuit, a second control circuit, a pumping control circuit, and a MOS transfer transistor; wherein said second non-overlap control circuit receives said oscillation signal, and generates a first and second non-overlap control signal having transition points that occur at different times; wherein said precharge circuit precharges said second pumping capacitor and said first and second bootstrap capacitors for a predetermined period; wherein said first step control circuit receives said second non-overlap control signal and generates a first precharging control signal to charge a third bootstrap capacitor to a first voltage level; wherein said second step control circuit receives said second non-overlap control signal and generates a second precharging control signal to charge said third bootstrap capacitor to a second voltage level; wherein said pumping control circuit receives said second non-overlap control signal and to generate a third precharging control signal to charge said third bootstrap capacitor to a third voltage level; wherein said MOS transfer transistor has a gate connected to said third bootstrap capacitor, and transfers charge stored in said second pumping capacitor to a body of said first MOS transistor as a well-bias voltage.