Multi-stage amplifier

1. A method comprising:

providing a plurality of power supply voltages;

selecting, in a common switched voltage stage, one of the plurality of power supply voltages in dependence on a reference signal representing a desired power supply voltage;

amplifying an input signal in a plurality of amplifiers;

distributing the one selected power supply voltage from the common switched voltage stage to a plurality of adjusting stages;

generating, in the plurality of adjusting stages, a plurality of adjusted selected power supply voltages, the number of the adjusted selected power supply voltages corresponding to the number of amplifiers, each adjusted selected power supply voltage tracking the reference signal in dependence on the one selected power supply voltage and the reference signal;

providing a plurality of copies of the reference signal for generating the plurality of adjusted selected power supply voltages, wherein providing the plurality of copies of the reference signal comprises distributing the reference signal to each of the plurality of adjusting stages using at least one splitter/buffer stage; and

providing each of the plurality of adjusted selected power supply voltages as the power supply voltage for a respective amplifier.

2. The method of claim 1 , wherein generating the plurality of adjusted selected power supply voltages comprises:

receiving each adjusted selected power supply voltage;

comparing each adjusted selected power supply voltage with the reference signal; and

in dependence thereon, generating an error signal to be added to the one selected power supply voltage in each of the adjusting stages to generate the plurality of adjusted selected power supply voltages.

3. The method of claim 1 , further comprising controlling the timing of the reference signal for the plurality of adjusting stages such that the adjusted selected power supply voltage for each amplifier is time-aligned to the input signal for each amplifier.

4. The method of claim 1 , wherein the common switched voltage stage provides a relatively lower frequency control loop for the plurality of amplifiers and wherein each of the plurality of adjusting stages provides an individual, relatively higher frequency control loop for each amplifier.

5. A method comprising:

providing a plurality of power supply voltages;

selecting, in a plurality of common switched voltage stages, one of the plurality of power supply voltages in dependence on a reference signal representing a desired power supply voltage;

amplifying an input signal in a plurality of amplifiers;

for each of the common switched voltage stages, distributing the one selected power supply voltage to a set of one or more adjusting stages associated with each of the common switched voltage stages;

generating, in the sets of adjusting stages, a plurality of adjusted selected power supply voltages, the number of the adjusted selected power supply voltages corresponding to the number of amplifiers, each adjusted selected power supply voltage tracking the reference signal in dependence on the one selected power supply voltage and the reference signal; and

providing each of the plurality of adjusted selected power supply voltages as the power supply voltage for a respective amplifier.

6. The method of claim 5 , further comprising distributing the reference signal to the plurality of common switched voltage stages for the selecting.

7. The method of claim 6 , further comprising distributing the reference signal to each set of one or more adjusting stages associated with each of the common switched voltage stages for the generating.

8. The method of claim 7 , wherein distributing the reference signal to each set comprises splitting and buffering the reference signal.

9. The method of claim 5 , wherein the number of the common switched voltage stages is m and wherein the number of the adjusting stages associated with each of the common switched voltage stages is n, where m and n are positive integers.

10. The method of claim 9 , wherein the number n of the adjusting stages is different for at least two of the common switched voltage stages.

11. The method of claim 5 , further comprising controlling the timing of the reference signal for the sets of adjusting stages such that the adjusted selected power supply voltage for each amplifier is time-aligned to the input signal for each amplifier.