High efficiency amplification
A radio frequency amplification stage comprising: an amplifier for receiving an input signal to be amplified and a power supply voltage; and a power supply voltage stage for supplying said power supply voltage, comprising: means for providing a reference signal representing the envelope of the input signal; means for selecting one of a plurality of supply voltage levels in dependence on the reference signal; and means for generating an adjusted selected power supply voltage, comprising an ac amplifier for amplifying a difference between the reference signal and one of the selected supply voltage level or the adjusted selected supply voltage level, and a summer for summing the amplified difference with the selected supply voltage to thereby generate the adjusted supply voltage.
1. An apparatus comprising:
a controller arranged to receive a digital envelope signal, the controller comprising:
a digital-to-analog converter for converting the digital envelope signal into an analog envelope signal; and
a digital controller for generating a digital control signal for a switching stage in dependence on the digital envelope signal,
a modulated supply stage comprising:
a switching stage for receiving the digital control signal and for selecting one of a plurality of supply voltages in dependence on the digital control signal;
a combiner for combining the selected supply voltage with an error signal, and for providing a power supply signal; and
an error amplifier for receiving the analog input signal and the output of the combiner and for generating the error signal;
an analog interface for connecting the analog input signal from the controller to the modulated stage; and
a digital interface for connecting the digital control signal from the controller to the modulated supply stage.
2. The apparatus of claim 1 wherein the controller comprises a digital delay stage for delaying the input to the digital to analog converter.
3. An amplification stage comprising a power amplifier and an apparatus according to claim 1 , the apparatus being adapted to provide a power supply to the power amplifier.
4. The amplification stage of claim 3 wherein the power amplifier is arranged to amplify a signal from which the digital envelope signal is derived.
5. The amplification stage of claim 4 comprising a further analog interface, the signal for the power amplifier to amplify being provided on the further analog interface.
6. The apparatus of claim 1 wherein the controller is a baseband controller.
7. A method of controlling an amplification stage including an amplifier and an envelope tracking power supply for the amplifier, comprising:
receiving a digital envelope signal;
converting the digital envelope signal into an analog envelope signal;
providing the analog envelope signal on an analog interface;
generating a digital control signal in dependence on the digital envelope signal;
providing the digital control signal to a power supply switching stage on a digital interface;
connecting one of a plurality of power supply voltages to an output of the switching stage in dependence on the digital control signal;
combining the connected power supply voltage and an error signal to generate the supply voltage for the amplifier; and
amplifying the difference between the supply voltage for the amplifier and the analog envelope signal to generate the error signal.
8. The method of claim 7 further comprising delaying the input to the digital to analog converter.
9. The method of claim 7 further comprising providing a power supply to the power amplifier.
10. The method of claim 9 further comprising amplifying a signal from which the digital envelope signal is derived.