Power supply arrangement for multi-stage amplifier

1. A multi-stage amplifier comprising:

a driver amplifier stage;

a power amplifier stage;

a switched supply stage arranged to provide a supply voltage to the driver amplifier stage in dependence on an average power of a signal to be amplified;

an envelope tracking modulated power supply stage arranged to provide a supply voltage to the power amplifier stage in dependence on an instantaneous power of the signal to be amplified, wherein the envelope tracking modulated power supply stage is configured to track an envelope of the signal to be amplified faster than the switched supply stage;

means for determining an average of the supply voltage provided by the envelope tracking modulated power supply stage, wherein the supply voltage is provided to the driver amplifier stage in dependence upon the determined average; and

a sample-and-hold stage for sampling the determined average.

2. The multi-stage amplifier of claim 1 wherein the switched supply stage selects one of a plurality of supply voltages generated in the envelope tracking modulated power supply stage.

3. The multi-stage amplifier of claim 1 further comprising means for determining the instantaneous power and the average power, wherein the average power is determined over a predetermined time interval.

4. The multi-stage amplifier of claim 1 wherein the means for determining the average of the supply voltage provided by the envelope tracking modulated power supply stage comprises a low pass filter.

5. The multi-stage amplifier of claim 1 wherein the switched supply stage is controlled by the determined average.

6. The multi-stage amplifier of claim 1 , wherein the switched and envelope tracking modulated power supply stages are arranged to selectively provide supply voltages to the driver and power amplifier stages, wherein in a first mode of operation a signal is amplified by the driver and power amplifier stages, the switched supply stage is selected to provide a supply voltage to the driver amplifier stage, and the envelope tracking modulated power supply stage is selected to provide a supply voltage to the power amplifier stage, and in a second mode of operation the power amplifier stage is bypassed, the signal is amplified by the driver amplifier stage, and the envelope tracking modulated power supply stage is selected to provide a supply voltage to the driver amplifier stage.

7. A method of amplifying a signal in an amplification stage comprising a driver amplifier stage; a power amplifier stage; a switched supply stage; and an envelope tracking modulated power supply stage, the method comprising:

providing the switched supply stage to provide a supply voltage to the driver amplifier stage in dependence on an average power of a signal to be amplified;

providing the envelope tracking modulated power supply stage to provide a supply voltage to the power amplifier stage in dependence on an instantaneous power of the signal to be amplified, wherein the envelope tracking modulated power supply tracks an envelope of the signal to be amplified faster than the switched supply stage;

determining an average of the supply voltage provided by an envelope tracking modulated power supply stage;

sampling the determined average; and

providing the supply voltage to the driver amplifier stage in dependence upon the determined average.

8. The method of claim 7 wherein the switched supply stage selects one of a plurality of supply voltages generated in the envelope tracking modulated power supply stage.

9. The method of claim 7 wherein determining the average of the supply voltage provided by the envelope tracking modulated power supply stage comprises low pass filtering the supply voltage.

10. The method of claim 7 further comprising controlling the switched supply stage based on the determined average.

11. The method of claim 7 , wherein the switched and envelope tracking modulated power supply stages selectively provide supply voltages to the driver and power amplifier stages, wherein in a first mode of operation a signal is amplified by the driver and power amplifier stages, the switched supply stage is selected to provide a supply voltage to the driver amplifier stage, and the envelope tracking modulated power supply stage is selected to provide a supply voltage to the power amplifier stage, and in a second mode of operation the power amplifier stage is bypassed, the signal is amplified by the driver amplifier stage, and the envelope tracking modulated power supply stage is selected to provide a supply voltage to the driver amplifier stage.