Patent ID: 6320797
Filing Date: 2001-11-20
Classification: G11C

Abstract:
A charge pump circuit, comprising:a plurality of charge pump stages coupled in series, each of the charge pump stages including an input terminal, an output terminal, a clock terminal, a capacitor, and a switch, the capacitor of each charge pump stage being coupled between the clock terminal and the input terminal, and the switch of each charge pump stage being coupled between the input terminal and the output terminal, the input terminal of a first charge pump stage in the series being coupled to a voltage source and the output terminal of a last charge pump stage in the series being coupled to a pumped voltage output terminal, the switches of all charge pump stages but the last charge pump stage being selectively closed to allow current to flow in a first direction and being selectively opened to prevent current flow in a second direction that is opposite the first direction, the switch of the last charge pump stage having a control input that is coupled to a control terminal;a clocking circuit generating first and second digital signals that are the complement of each other, the clocking circuit being coupled to supply the first and second digital signals to the clock terminals of the respective charge pump stages with the charge pump stages that receive the first digital signal alternating with the charge pump stages that receive the second digital signal; anda control circuit coupled to the pumped voltage output terminal and the control terminal of the last charge pump stage, the control circuit applying a control signal to the control terminal to allow current to flow in the first direction when the absolute value of a pumped voltage at the pumped voltage output terminal has a magnitude that is less than a predetermined value and to prevent current from flowing in the first direction when the absolute value of the pumped voltage at the pumped voltage output terminal has a magnitude that is greater than the predetermined value, the control circuit comprising:a ratio circuit coupled to the pumped voltage output terminal and operable to develop a ratio output voltage having a value that is proportional to the pumped voltage;a comparator having a first terminal coupled to the ratio circuit and a second terminal adapted to receive a reference voltage, the comparator operable to compare the ratio output voltage to the reference voltage and developing an active compare signal responsive to the comparison indicating the reference voltage is less than the ratio output voltage and developing an inactive compare signal responsive to the comparison indicating the reference voltage is greater than the ratio output voltage; andan amplifier having an input coupled to the comparator and generating an amplified compare signal on an output, the amplifier generating the active control signal indicating the reference voltage is less than the ratio output voltage, and generating the inactive control signal indicating the reference voltage is greater than the ratio output voltage.