Power supply pre-distortion
There is disclosed a method of generating a supply voltage ( 230 ) for a power amplifier ( 114 ) arranged to amplify an input signal ( 228 ), comprising: generating ( 104 ) a target supply voltage tracking the input signal ( 228 ); predistorting ( 400 ) the target supply voltage to compensate for effects on a supply voltage in the amplifier ( 114 ); and generating ( 102 ) the supply voltage for the amplifier ( 114 ) in dependence on the predistorted target supply voltage ( 414 ).
1. A method of generating a supply voltage for a power amplifier arranged to amplify an input signal, comprising:
generating a target supply voltage tracking the input signal;
pre-distorting the target supply voltage to compensate for the effects applied to the supply voltage between an input terminal of the amplifier and a node of an active element of the amplifier to which the modulated supply voltage is applied; and
generating the supply voltage for the amplifier in dependence on the pre-distorted target supply voltage.
2. The method according to claim 1 wherein the step of pre-distorting compensates for the effects of at least one capacitor in the supply feed network of the amplifier.
3. The method according to claim 1 wherein the step of pre-distorting compensates for shunt capacitance presented by the active element of the amplifier.
4. The method of claim 1 wherein the step of generating the target supply voltage comprises generating an envelope signal representing the envelope of the signal to be amplified.
5. The method of claim 4 wherein the step of generating the target supply voltage comprises shaping the generated envelope signal.
6. The method of claim 4 wherein the step of generating the target supply voltage comprises modulating the generated envelope signal.
7. The method of claim 1 wherein the step of generating the supply voltage comprises modulating the pre-distorted target supply voltage.
8. A supply voltage stage for a power amplifier arranged to amplify an input signal, comprising:
a tracking voltage generator for generating a target supply voltage tracking the input signal;
a pre-distortion stage for pre-distorting the target supply voltage to compensate for effects on a supply voltage in the amplifier, wherein the supply voltage for the amplifier is connected at a supply voltage terminal of the amplifier, the pre-distortion stage being configured to compensate for any effect on the supply voltage in the amplifier path between the supply voltage terminal and an active element of the amplifier which provides the amplification of the input signal; and
a supply voltage generator for generating the supply voltage for the amplifier in dependence on the pre-distorted target supply voltage.
9. The supply voltage stage of claim 8 wherein the active element is a transistor, and the amplifier path is between the supply voltage terminal of the amplifier and a supply mode of the transistor.
10. The supply voltage stage of claim 9 wherein the amplifier path attenuates or delays the supply voltage delivered to the active element.