Programmable supply voltage regulator for oscillator

1. A circuit comprising:

a programmable regulator that generates a regulated supply voltage using an input voltage and that changes the regulated supply voltage from a first voltage to a second voltage in response to a first control signal that is generated based on user configuration data, wherein the first and the second voltages are generated using charge from the input voltage; and

an oscillator that varies a frequency of a periodic output signal within a frequency range in response to changes in a control voltage, wherein the regulated supply voltage drives the oscillator, and the frequency range of the periodic output signal of the oscillator varies when the first control signal causes the regulated supply voltage to change from the first voltage to the second voltage.

2. The circuit defined in claim 1 wherein the programmable regulator comprises:

a programmable current source; and

an operational amplifier having an input that is coupled to the programmable current source.

3. The circuit defined in claim 2 wherein the programmable regulator further comprises:

a first transistor coupled to receive the input voltage; and

a second transistor coupled to receive current from the first transistor, wherein current through the second transistor is controlled by the operational amplifier, and the operational amplifier controls the regulated supply voltage at a terminal of the second transistor based on a reference voltage generated by the programmable current source.

4. The circuit defined in claim 3 wherein the programmable regulator further comprises a filter that comprises:

a resistor coupled between a control input of the first transistor and the input voltage;

a capacitor coupled to the resistor; and

a constant current source coupled to the control input of the first transistor.

5. The circuit defined in claim 1 wherein the programmable regulator comprises a programmable current source, and the programmable current source comprises:

a current mirror circuit comprising first, second, and third transistors, wherein a control input of the first transistor is coupled to a control input of the second transistor; and

a switch coupled to the control input of the first transistor and a control input of the third transistor, wherein a conductive state of the switch is controlled by the first control signal.

6. The circuit defined in claim 1 wherein the programmable regulator varies the regulated supply voltage between at least three discrete voltages in response to the first control signal and a second control signal, and wherein the oscillator varies the frequency range of the periodic output signal when the regulated supply voltage changes between the three discrete voltages.

7. The circuit defined in claim 6 wherein the programmable regulator varies the regulated supply voltage between at least five discrete voltages in response to the first control signal, the second control signal, and a third control signal, wherein the first, the second, and the third control signals are digital control signals.

8. The circuit defined in claim 7 wherein the circuit is a programmable logic integrated circuit, and the first, the second, and the third digital control signals are generated in response to user configuration data stored in memory on the programmable logic integrated circuit.

9. The circuit defined in claim 1 wherein the oscillator comprises:

first and second varactors; and

an inductor coupled to the first and the second varactors, wherein capacitances of the first and the second varactors vary in response to variations in the regulated supply voltage that are caused by the first control signal.

10. The circuit defined in claim 1 wherein the oscillator is a voltage-controlled oscillator that generates periodic output clock signals.

11. The circuit defined in claim 1 further comprising:

a phase-frequency detector;

a charge pump coupled to the phase-frequency detector; and

a loop filter coupled to the charge pump and the oscillator, wherein the phase-frequency detector, the charge pump, the loop filter, and the oscillator are part of a phase-locked loop circuit.

12. A circuit comprising:

an oscillator that generates a periodic output signal, wherein a frequency of the periodic output signal varies between a maximum frequency and a minimum frequency in response to variations in a control voltage; and

a programmable regulator that provides a regulated supply voltage to the oscillator using an input voltage and that varies the regulated supply voltage between first and second voltages in response to a first control signal, wherein the programmable regulator comprises a programmable current source that varies an output current in response to the first control signal, both of the first and the second voltages are generated with current from the input voltage, and the maximum and the minimum frequencies of the periodic output signal of the oscillator change in response to the first control signal causing the regulated supply voltage to change from the first voltage to the second voltage.

13. The circuit defined in claim 12 wherein the oscillator and the programmable regulator are part of a phase-locked loop, and the control voltage is generated by a charge pump.

14. The circuit defined in claim 12 wherein

the programmable current source varies the output current in response to the first control signal and a second control signal, and wherein the programmable regulator varies the regulated supply voltage between the first, the second, and third voltages in response to variations in the output current of the programmable current source that are caused by changes in the first and the second control signals.

15. The circuit defined in claim 14 wherein the programmable regulator further comprises:

an amplifier having an input coupled to the programmable current source; and

first and second transistors coupled in series between the input voltage and the oscillator, wherein the amplifier controls a current through the second transistor to affect the regulated supply voltage.

16. The circuit defined in claim 12 wherein the programmable regulator varies the regulated supply voltage between at least three discrete voltages in response to the first control signal and a second control signal, the maximum and the minimum frequencies of the periodic output signal change in response to the first and the second control signals causing the regulated supply voltage to change between the three discrete voltages, and the three discrete voltages are generated with current from the input voltage.

17. The circuit defined in claim 16 wherein the circuit is a programmable logic integrated circuit, and the first and the second control signals are generated in response to user configuration data stored in memory on the programmable logic integrated circuit.

18. A method for shifting a center frequency of an oscillator circuit, the method comprising:

generating a regulated supply voltage based on an input voltage using a programmable regulator circuit;

varying the regulated supply voltage between first and second voltages by varying a first current generated by a programmable current source in response to a first control signal, wherein the first and the second voltages are generated using charge from the input voltage;

driving the oscillator circuit using the regulated supply voltage;

varying a frequency of an output clock signal of the oscillator circuit in response to a control voltage; and

varying a center frequency of the output clock signal of the oscillator circuit when the programmable regulator circuit varies the regulated supply voltage between the first and the second voltages in response to the first control signal.

19. The method defined in claim 18 wherein varying the regulated supply voltage between the first and the second voltages further comprises adjusting a second current through a transistor using an amplifier in response to varying the first current generated by the programmable current source.

20. The method defined in claim 18 wherein varying the regulated supply voltage between the first and the second voltages further comprises varying the regulated supply voltage between at least three voltages in response to the first control signal and a second control signal, and

wherein varying the center frequency of the output clock signal of the oscillator circuit when the programmable regulator circuit varies the regulated supply voltage between the first and the second voltages in response to the first control signal further comprises varying the center frequency of the output clock signal when the programmable regulator circuit varies the regulated supply voltage between the second voltage and a third voltage, wherein the third voltage is generated using charge from the input voltage.

21. A circuit comprising:

a programmable current source;

an operational amplifier that generates a regulated supply voltage using an input voltage controlled by the programmable current source and that changes the regulated supply voltage from a first voltage to a second voltage in response to a first control signal; and

an oscillator that varies a frequency of a periodic output signal within a frequency range in response to changes in a control voltage, wherein the regulated supply voltage drives the oscillator, and the frequency range of the periodic output signal of the oscillator varies when the first control signal causes the regulated supply voltage to change from the first voltage to the second voltage.