Passive bootstrapped charge pump for NMOS power device based regulators

1. A charge pump in a low dropout regulator comprising:

an amplifier having an output;

a first capacitor coupled to the output and to a gate of a pass transistor;

a first plurality of switches operable to couple a second capacitor between an output of the low dropout regulator and to a ground in a first clock phase such that the second capacitor charges to an output voltage; and

a second plurality of switches operable to couple the second capacitor in parallel to the first capacitor in a second clock phase such that the second capacitor charges the first capacitor.

2. The charge pump of claim 1 , wherein the plurality of switches include at least one of a complementary switch, an n-type metal oxide semiconductor field effect transistor switch and a p-type metal oxide semiconductor field effect transistor switch.

3. The charge pump of claim 1 , wherein the plurality of switches functions in response to a plurality of control signals.

4. The charge pump of claim 3 , wherein an oscillator and a level shifter together generate the plurality of control signals.

5. A charge pump in a low dropout regulator, comprising:

an amplifier having an output;

a first capacitor coupled to the output and to a gate of a pass transistor;

a first plurality of switches that is operable to couple a second capacitor between an output of the low dropout regulator and to a ground in a first clock phase such that the second capacitor charges to an output voltage, and that is operable to couple a third capacitor in parallel to the first capacitor such that the third capacitor charges the first capacitor; and

a second plurality of switches that is operable to couple the third capacitor between an output of the low dropout regulator and to a ground in a second clock phase such that the second capacitor charges to an output voltage, and that is operable to couple the second capacitor in parallel to the first capacitor such that the second capacitor charges the first capacitor.

6. The charge pump of claim 5 , wherein the first plurality of switches and the second plurality of switches function in response to a plurality of control signals.

7. The charge pump of claim 6 , wherein an oscillator and a level shifter together generate the plurality of control signals.

8. The charge pump of claim 7 , wherein the level shifter translates a clock signal that is generated by the oscillator to appropriate voltage and polarity that controls each switch of the first plurality of switches and the second plurality of switches.

9. The charge pump of claim 5 and further comprising:

an external capacitor at the output of the low dropout regulator, wherein the external capacitor provides a charge that compensates a parasitic capacitance of the second capacitor and third capacitor during the first clock phase and the second clock phase.

10. The charge pump of claim 5 , whereby startup time of the low dropout regulator and transient glitch is reduced.

11. The low dropout regulator of claim 5 , whereby ripple at the output of the low dropout regulator is reduced.

12. A method for operating a charge pump in a low dropout regulator, comprising:

charging a second capacitor to an output voltage of the low dropout regulator in a first clock phase, the second capacitor being coupled between an output of the low dropout regulator and to a ground; and

charging a first capacitor using the second capacitor in a second clock phase, the first capacitor being coupled between an output of an amplifier of the low dropout regulator and a gate of a pass transistor.

13. The method of claim 12 , wherein charging a second capacitor and charging a first capacitor comprising controlling a plurality of switches using a plurality of control signals.

14. The method of claim 13 , wherein controlling a plurality of switches generating the plurality of control signals using an oscillator and a level shifter.