Voltage regulator with shunt feedback

1. A voltage regulator configured to receive a supply voltage from a voltage supply and provide a regulated voltage to digital circuitry, the voltage regulator comprising:

first circuitry configured to inhibit high frequency energy generated by the digital circuitry from transmitting into the voltage supply;

second circuitry configured to inhibit low frequency energy generated by the digital circuitry from transmitting into the voltage supply; and

third circuitry, having two current sources and two transistors respectively connected to the two current sources, configured to maintain the regulated voltage at a substantially constant value in response to a first current drawn by the digital circuitry.

2. The voltage regulator of claim 1 wherein the third circuitry is configured to increase a second current drawn by the third circuitry in response to the first current decreasing, and wherein the third circuitry is configured to decrease the second current drawn by the third circuitry in response to the first current increasing.

3. The voltage regulator of claim 1 wherein the third circuitry is configured to provide shunt feedback.

4. The voltage regulator of claim 1 wherein the third circuitry is configured to provide a reference voltage as the regulated voltage.

5. The voltage regulator of claim 1 wherein the third circuitry includes a transistor that is configured to provide shunt feedback.

6. The voltage regulator of claim 1 wherein the third circuitry includes a frequency compensation circuit.

7. The voltage regulator of claim 1 wherein the first circuitry includes a capacitive element configured to inhibit the high frequency energy from transmitting into the voltage supply.

8. The voltage regulator of claim 1 wherein the second circuitry includes a constant current source configured to inhibit the low frequency energy from transmitting into the voltage supply.

9. The voltage regulator of claim 8 wherein the constant current source is configured to generate a second current, wherein the third circuitry is configured to draw a third current that is approximately equal to the second current minus the first current.

10. The voltage regulator of claim 1 wherein the second circuitry and a voltage reference are adjustable to allow the regulated voltage to be adjusted.

11. A method performed by a voltage regulator that includes current sources and transistors, the method comprising:

receiving a supply voltage from a voltage supply;

providing a regulared voltage to first circuitry;

inhibiting high frequency energy generated by the first circuitry using the regulated voltage from transmitting into the voltage supply;

inhibiting low frequency energy generated by the first circuitry using the regulated voltage from transmitting into the voltage supply; and

maintaining the regulated voltage at a substantially constant value in response to a first current drawn by the first circuitry, using two of the current sources respectively connected to two of the transistors.

12. The method of claim 11 further comprising:

increasing a second current drawn by the voltage regulator in response to the first current decreasing; and

decreasing the second current drawn by the voltage regulator in response to the first current increasing.

13. The method of claim 11 further comprising:

providing shunt feedback in the voltage regulator.

14. The method of claim 11 further comprising:

providing a reference voltage as the regulated voltage.

15. The method of claim 11 further comprising:

providing a frequency compensation circuit in the voltage regulator.

16. The method of claim 11 further comprising:

inhibiting the high frequency energy from transmitting into the voltage supply using a capacitive element.

17. The method of claim 11 further comprising:

inhibiting the low frequency energy from transmitting into the voltage supply using a constant current source.

18. The method of claim 11 further comprising:

generating a second current with a constant current source; and

drawing a third current in the voltage regulator that is approximately equal to the second current minus the first current.

19. The method of claim 11 further comprising:

adjusting the regulated voltage using second circuitry that comprises control circuitry.

20. A system comprising:

circuitry; and

a voltage regulator circuitry, having two current sources and two transistors respectively connected to the two current sources, configured to receive a supply voltage from a voltage supply and provide a regulated voltage to the circuitry;

wherein the voltage regulator is configured to inhibit high frequency energy generated by the circuitry from transmitting into the voltage supply, wherein the voltage regulator is configured to inhibit low frequency energy generated by the circuitry from transmitting into the voltage supply, and wherein the voltage regulator is configured to maintain the regulated voltage at a substantially constant value in response to a first current drawn by the circuitry.

21. The system of claim 20 wherein the voltage regulator is configured to provide shunt feedback.

22. The system of claim 20 wherein the voltage regulator is adjustable to allow the regulated voltage to be adjusted.

23. A communications device comprising:

an antenna;

a mobile communications system configured to communicate with a remote host using the antenna and including a voltage supply, circuitry, and a voltage regulator configured to receive a supply voltage from the voltage supply and provide a regulated voltage to the circuitry; and

an input/output system configured to communicate with the mobile communications system;

wherein the voltage regulator circuitry has two current sources and two transistors respectively connected to the two current sources and is configured to inhibit high frequency energy generated by the circuitry from transmitting into the voltage supply, wherein the voltage regulator is configured to inhibit low frequency energy generated by the circuitry from transmitting into the voltage supply, and wherein the voltage regulator is configured to maintain the regulated voltage at a substantially constant value in response to a first current drawn by the circuitry.

24. The communications device of claim 23 wherein the voltage regulator is configured to provide shunt feedback.

25. The communications device of claim 23 wherein the voltage regulator includes a frequency compensation circuit.

26. The communications device of claim 23 wherein the voltage regulator is adjustable to allow the regulated voltage to be adjusted.