Adaptive voltage scaling circuitry

1. A circuit comprising:

a first voltage regulator to produce a first regulated supply voltage for a main circuit;

a second voltage regulator to produce a second regulated supply voltage;

a plurality of test circuits to produce respective test signals, each having a characteristic dependent on the second regulated supply voltage; and

a controller to control the second voltage regulator to adjust the second regulated supply voltage to one or more threshold levels determined based only on changes detected in the characteristics of the respective test signals produced by the plurality of test circuits,

the controller to control the first voltage regulator to adjust the first regulated supply voltage based on a threshold level of the second regulated supply voltage among the one or more threshold levels having a maximum value.

2. The circuit of claim 1 , wherein the adjusted first regulated supply voltage is different than the threshold level by a margin.

3. The circuit of claim 1 , wherein the plurality of test circuits are representative of a portion of the main circuit.

4. The circuit of claim 3 , wherein the plurality of test circuits comprise circuitry identical to circuitry in the main circuit.

5. The circuit of claim 1 , wherein the characteristic includes at least one of a frequency, a bit count, a bit sequence, bit errors, logic value, a voltage level, a current level and signal quality.

6. The circuit of claim 1 , wherein the main circuit and the plurality of test circuits are on the same circuit.

7. The circuit of claim 1 , wherein the controller further:

controls the second voltage regulator to repeatedly adjust the second regulated supply voltage to determine an updated threshold level; and

controls the first voltage regulator to adjust the first regulated supply voltage based on the updated threshold level.

8. The circuit of claim 1 , wherein the second voltage regulator is powered from the first regulated supply voltage.

9. The circuit of claim 1 , wherein at least some of the characteristics are different from each other.

10. The circuit of claim 1 , wherein the plurality of test circuits are distributed at different locations in the circuit.

11. The circuit of claim 1 , further comprising a corresponding plurality of second voltage regulators and controllers for the plurality of test circuits, the plurality of controllers to determine a plurality of threshold levels corresponding to the plurality of test circuits, the circuit further comprising a master controller to control the first voltage regulator to adjust the first regulated supply voltage.

12. The circuit of claim 1 , wherein the controller controls the first voltage regulator and the second voltage regulator during operation of circuitry that comprise the circuit.

13. A method in a circuit comprising:

producing a first regulated supply voltage for a main circuit;

producing at least one second regulated supply voltage for a plurality of test circuits;

determining a plurality of threshold levels for the plurality of test circuits, including:

producing one or more test signals, each having a characteristic dependent on the at least one second regulated supply voltage; and

adjusting the at least one second regulated supply voltage to a threshold level that is determined based only on changes detected in the characteristic of the one or more test signals produced by said each test circuit; and

adjusting the first regulated supply voltage based on a maximum threshold level among the plurality of threshold levels.

14. The method of claim 13 , further comprising adjusting the first regulated supply voltage to differ from the maximum threshold level by a margin.

15. The method of claim 13 , further comprising producing the at least one second regulated supply voltage from the first regulated supply voltage.

16. The method of claim 13 , further comprising determining the plurality of threshold levels for the plurality of test circuits at different locations in the circuit.

17. The method of claim 13 , further comprising powering the plurality of test circuits with a respective plurality of independently produced second regulated supply voltages, and adjusting the plurality of second regulated supply voltages independently of each other to determine the plurality of threshold levels.

18. The circuit of claim 1 , wherein the controller controls the second voltage regulator without the controller comparing the respective test signals to a reference signal.

19. The circuit of claim 1 , wherein the controller controls the second voltage regulator to adjust the second regulated supply voltage to the one or more threshold levels based on a relation between the respective test signals.

20. The circuit of claim 1 , wherein the respective test signals are digital signals.