Micropower gate charge pump for power MOSFETS

Claim 2

A circuit for charging the gate of a field-effect transistor to a boosted voltage in excess of a supply voltage, the circuit comprising: a capacitive voltage multiplier having an input for receiving an oscillating signal and an output for producing the boosted voltage, the multiplier operating to cause the boosted voltage to increase beyond the supply voltage at a rate determined at least in part by the frequency of the oscillating signal; an oscillator coupled to the multiplier to produce the oscillating signal at a frequency selected in response to the receipt of a control signal, the selected frequency causing the boosted voltage to increase beyond the supply voltage at a predetermined rate; and a control circuit coupled to sense the voltage at the gate of the field-effect transistor and to responsively generate the control signal such that the oscillator produces the oscillating signal at the selected frequency when the gate voltage is less than a frequency switching voltage, and the oscillator ceases to produce the oscillating signal at the selected frequency when the gate voltage exceeds the frequency switching voltage, whereby the power consumption of the circuit is reduced when the gate voltage exceeds the frequency switching voltage.

Claim 3

The circuit of claim 1, wherein: the oscillator comprises a current-controlled oscillator and the control signal is a current; and the control circuit includes a voltage comparator.

Claim 6

The method of claim 3, wherein: the control signal is a current signal; and the step of voltage sensing further comprises comparing the gate voltage to a predetermined voltage.

Claim 7

A circuit for charging the gate of a field-effect transistor to a voltage boosted in excess of a supply voltage, the circuit comprising: voltage multiplier means for producing the boosted voltage in response to the receipt of an oscillating signal, said means operating such that the boosted voltage increases beyond the supply voltage at a rate determined at least in part by the oscillation frequency of the oscillating signal; oscillating means for producing the oscillating signal at a frequency selected by a control signal, said selected frequency chosen to cause the boosted voltage produced by the voltage multiplier to increase beyond the supply voltage at a predetermined rate; and means coupled to sense the voltage at the gate of the field-effect transistor for responsively generating the control signal to cause the oscillating means to produce the oscillating signal at the selected frequency when the gate voltage is less than a frequency switching voltage and to cease producing the oscillating signal at the selected frequency when the gate voltage exceeds the frequency switching voltage, whereby the power consumption of the circuit is reduced when the gate voltage exceeds the frequency switching voltage.

Claim 8

A circuit for charging the gate of a field-effect transistor to a voltage boosted in excess of a supply voltage, the circuit comprising: voltage multiplier means for producing the boosted voltage in response to the receipt of an oscillating signal, said means operating such that the boosted voltage increases beyond the supply voltage at a rate determined at least in part by the oscillation frequency of the oscillating signal; oscillating means for producing the oscillating signal at a frequency selected by a control signal, said selected frequency chosen to cause the boosted voltage produced by the voltage multiplier to increase beyond the supply voltage at a predetermined rate; and means coupled to sense the voltage at the gate of the field-effect transistor for responsively generating the control signal to cause the oscillating means to produce the oscillating signal at the selected frequency when the gate voltage is less than a frequency switching voltage and to cease producing the oscillating signal at the selected frequency when the gate voltage exceeds the frequency switching voltage, whereby the power consumption of the circuit is reduced when the gate voltage exceeds the frequency switching voltage.

Claim 9

The circuit of claim 5, wherein: the oscillating means comprises a current-controlled oscillator wherein the control signal is a current signal; and the voltage sensing means comprises a voltage comparator.

Claim 10

An improvement in a method for operating a charge-pump circuit for boosting a voltage applied to a gate of a field-effect transistor beyond a supply voltage, the circuit including a capacitive multiplier for producing the boosted voltage in response to an oscillating signal coupled to the multiplier, the improvement in the method comprising the steps of: initially generating the oscillating signal at a selected frequency to cause the gate voltage to be boosted beyond the supply voltage at a first rate; and ceasing to generate the oscillating signal at the selected frequency when the gate voltage of the transistor has been initially sufficiently boosted such that the power consumption of the circuit is reduced by ceasing to generate the oscillating signal at the selected frequency.

Claim 11

An improvement in a method for operating a charge-pump circuit for boosting a voltage applied to a gate of a field-effect transistor beyond a supply voltage, the circuit including a capacitive multiplier for producing the boosted voltage in response to an oscillating signal coupled to the multiplier, the improvement in the method comprising the steps of: initially generating the oscillating signal at a selected frequency to cause the gate voltage to be boosted beyond the supply voltage at a first rate; and ceasing to generate the oscillating signal at the selected frequency when the gate voltage of the transistor has been initially sufficiently boosted such that the power consumption of the circuit is reduced by ceasing to generate the oscillating signal at the selected frequency.

Claim 12

The improved method of claim 7, wherein the gate voltage has been sufficiently boosted when that voltage reaches a value which causes the transistor to be driven into enhancement under its expected operating conditions.

Claim 13

An improvement in a charge-pump circuit for boosting a voltage applied to a gate of a field-effect transistor beyond a supply voltage, the circuit including a capacitive multiplier for producing the boosted voltage in response to an oscillating signal coupled to the multiplier, the rate of boost being determined at least in part by the frequency of the oscillating signal, the improvement in the circuit comprising: a variable frequency oscillator for producing the oscillating signal at a selected frequency to cause the gate voltage to be boosted at a first rate; means for detecting when the gate voltage has been initially sufficiently boosted; and means responsive to said detecting means for generating the control signal when the gate voltage has been initially sufficiently boosted to cease the production of the oscillating signal at the selected frequency such that the power consumption of the circuit is reduced by ceasing to generate the oscillating signal at the selected frequency.

Claim 14

An improvement in a charge-pump circuit for boosting a voltage applied to a gate of a field-effect transistor beyond a supply voltage, the circuit including a capacitive multiplier for producing the boosted voltage in response to an oscillating signal coupled to the multiplier, the rate of boost being determined at least in part by the frequency of the oscillating signal, the improvement in the circuit comprising: a variable frequency oscillator for producing the oscillating signal at a selected frequency to cause the gate voltage to be boosted at a first rate; means for detecting when the gate voltage has been initially sufficiently boosted; and means responsive to said detecting means for generating the control signal when the gate voltage has been initially sufficiently boosted to cease the production of the oscillating signal at the selected frequency such that the power consumption of the circuit is reduced by ceasing to generate the oscillating signal at the selected frequency.

Claim 15

A circuit for charging a gate of a transistor to a boosted voltage in excess of a supply voltage, the transistor operating in a plurality of operational states each corresponding to a particular set of current-voltage characteristics of the transistor, the circuit comprising: an oscillator for generating a signal oscillating at at least a first selected frequency chosen in response to a control signal received by said oscillator; a charge-pump voltage multiplier coupled to the supply voltage, said multiplier having an input coupled for receiving the oscillating signal and an output coupled to produce at the gate of the transistor the boosted voltage, said multiplier operating to increase the boosted voltage beyond the supply voltage at a rate determined at least in part by the frequency of the oscillating signal; and means for detecting the operational state of the transistor and for responsively generating the control signal to cause the oscillator to generate the oscillating signal at the first selected frequency when the transistor is in a first operating state to boost the gate voltage beyond the supply voltage at a first rate, and to cease to generate the oscillating signal at the first selected frequency when the transistor is in a second operating state, whereby the power consumed by the circuit is reduced when the transistor is in the second operating state.

Claim 16

A circuit for charging a gate of a transistor to a boosted voltage in excess of a supply voltage, the transistor operating in a plurality of operational states each corresponding to a particular set of current-voltage characteristics of the transistor, the circuit comprising: an oscillator for generating a signal oscillating at at least a first selected frequency chosen in response to a control signal received by said oscillator; a charge-pump voltage multiplier coupled to the supply voltage, said multiplier having an input coupled for receiving the oscillating signal and an output coupled to produce at the gate of the transistor the boosted voltage, said multiplier operating to increase the boosted voltage beyond the supply voltage at a rate determined at least in part by the frequency of the oscillating signal; and means for detecting the operational state of the transistor and for responsively generating the control signal to cause the oscillator to generate the oscillating signal at the first selected frequency when the transistor is in a first operating state to boost the gate voltage beyond the supply voltage at a first rate, and to cease to generate the oscillating signal at the first selected frequency when the transistor is in a second operating state, whereby the power consumed by the circuit is reduced when the transistor is in the second operating state.

Claim 17

The circuit of claim 10, wherein: the oscillator comprises a current-controlled oscillator wherein the control signal is a current signal; and the operational state detecting means comprises a voltage comparator.

Claim 18

The circuit of claim 11, wherein the operational state detecting means monitors the voltage on the gate of the transistor, and wherein the second operating state of the transistor comprises a predetermined range of gate voltages in excess of a minimum predetermined voltage value.

Claim 19

The circuit of claim 12, wherein: the charge-pump voltage multiplier comprises two charge-pump capacitors and two inverters which are driven out of phase with each other by the oscillating signal, wherein the outputs of each inverter are each coupled to a different charge-pump capacitor.

Claim 20

The circuit of claim 13, wherein the control current signal takes on a first current value when the gate voltage is below the minimum predetermined gate voltage value and a second current value when the gate voltage exceeds the minimum predetermined gate voltage value.

Claim 21

The circuit of claim 14, wherein the operational state detecting means includes at least two diode-connected NMOS transistors with their corresponding p-wells connected to ground and wherein the transistors are coupled in series with a current source for providing a small bias current to the transistor diodes.

Claim 22

The circuit of claim 10, wherein the operational state detecting means monitors the current through the transistor and wherein the second operating state of the transistor comprises a predetermined range of transistor currents in excess of a minimum predetermined current value.