Electric power conversion systems – Current conversion – With voltage multiplication means
Reexamination Certificate
1997-06-17
2001-02-13
Nguyen, Matthew (Department: 2838)
Electric power conversion systems
Current conversion
With voltage multiplication means
Reexamination Certificate
active
06188590
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to charge pump circuits, and more particularly to a regulator system that can regulate the output voltage and current of charge pump circuits.
BACKGROUND OF THE INVENTION
A charge pump is a circuit that can generate an output voltage that is higher than the voltage supplied to the charge pump. One of the applications of charge pumps is to develop voltages for various modes of operation of flash EPROM (electrically programmable read only memory). The memory cells in flash EPROM are formed using so-called floating gate transistors in which the data is stored by charging or discharging the floating gate. These modes of operation generally require a high voltage.
The act of charging the floating gate is termed the “program” mode of a flash EPROM. This is typically accomplished using hot electron injection induced by establishing a large positive voltage between the gate and source, as much as 12 volts, and a positive voltage between the drain and source, for instance, 7 volts.
The act of discharging the floating gate is called the “erasing” mode of a flash EPROM. This erase function is typically carried out through Fowler-Nordheim tunneling induced by establishing a large positive voltage from the source to gate, while floating the drain of the memory cell. This positive voltage can be as much as 12 volts.
Some prior art flash EPROM devices require the application of an external high voltage in addition to a regular 3 or 5 volts supply voltage. Such an arrangement is undesirable because it complicates system design. Recently, many nonvolatile semiconductor memory device manufacturers (including flash EPROM manufacturers) place charge pumps on chips to generate the required high voltage for erasing and programming memory cells.
The output voltage of a charge pump needs to be regulated. Prior art systems use breakdown devices (such as zener diodes) or equivalent circuits that become conductive when voltage applied thereto exceeds a predetermined value. Although this arrangement can keep the output voltage below the predetermined value, a large amount of current needs to flow through the breakdown device. As a result, prior art regulator systems consume much power.
Because it is a low power system design, it is important to keep power consumption down. Consequently, there is a need to design a more efficient regulator system which consumes less power.
SUMMARY OF THE INVENTION
The present invention relates to a regulator system that can regulate the output current and voltage of a charge pump circuit. It is found that the output current drivability of many charge pump circuits can be adjusted by changing the amplitude and/or frequency of their associated driving clocks. This arrangement provides good regulation while power consumed by the inventive regulator is much lower than prior art regulators.
In providing for output circuit regulation to a charge pump circuit, the present invention comprises means for generating a set of at least one control signal as a function of the output current. The set of at least one control signal is coupled to a clock signal generation circuit that generates a set of clock signals having a respective magnitude and a frequency depending on this set of at least one control signal. This set of clock signals is then used to drive the charge pump circuit.
As an example, a higher clock signal amplitude or clock frequency will increase the output current driving capability of many charge pump circuits. Thus, if the actual output current is lower than desired, the set of clock signals needs to have a higher amplitude and/or higher frequency. As a result, the output current can be increased. Similarly, if the actual output current is higher than desired, the set of clock signals needs to have a lower amplitude and/or lower frequency.
In one embodiment of the present invention, the means for generating control signals comprises a plurality of current mirrors and associated transistors used as resistors. Various voltages are generated by currents in these current mirrors flowing through their associated transistors. These voltages are decoded into additional control signals.
The present regulator system further comprises an amplitude modulation (AM) circuit that generates a modulation voltage having a magnitude depending on these additional control signals. This regulator system also comprises a frequency modulation (FM) circuit that generates a clock signal having a frequency depending on these additional control signals. The modulation voltage and clock signal are applied to a clock generation circuit that generates multiple-phase clock signals having a variable magnitude. The multiple-phase clock signals are applied to a charge pump circuit. By changing the magnitude and frequency of these multiple-phase signals, the output current of the charge pump circuit can be regulated.
These and other features of the present invention will become apparent from the following description when read in conjunction with the drawings.
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Chang Kuen-Long
Chuang Weitong
Hung Chun-Hsiung
Haynes Mark A.
Haynes & Beffel LLP
Macronix International Co. Ltd.
Nguyen Matthew
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