Correcting distortions at output of power amplifier

1. A method, comprising:

receiving a distorted time-varying supply voltage from a power supply;

determining at least one correction factor for a distortion on a radio frequency output signal of a power amplifier on the basis of estimated characteristics of the distorted time-varying supply voltage; and

applying the at least one correction factor to an input signal of the power amplifier.

2. The method according to claim 1 , wherein the characteristics of the distorted time-varying supply voltage comprise at least one of the following: a level of the supply voltage, a phase of the supply voltage and a frequency of the supply voltage.

3. The method according to claim 1 , further comprising:

sampling the distorted time-varying supply voltage for a number of predefined time periods at more than one time instant;

subtracting a nominal value of a supply voltage characteristic at each time period from the samples at the corresponding time period;

averaging the samples at corresponding time instants over more than one time period;

generating a model for the distortion introduced to the time-varying supply voltage by the power supply on the basis of the samples; and

estimating the characteristics of the distorted time-varying supply voltage on the basis of the model.

4. The method according to claim 1 , further comprising:

taking the amplitude of the input signal of the power amplifier into account when determining the at least one correction factor.

5. The method according to claim 1 , wherein the at least one correction factor is an inverse of the distortion on the radio frequency output signal of the power amplifier.

6. The method according to claim 1 , wherein the power supply is a switched mode power supply.

7. An apparatus, comprising:

a processor; and

a memory including computer program code, the memory and the computer program code configured to, with the processor, cause the apparatus at least to determine at least one correction factor for a distortion on a radio frequency output signal of a power amplifier on the basis of estimated characteristics of a distorted time-varying supply voltage received from a power supply, and

apply the at least one correction factor to an input signal of the power amplifier.

8. The apparatus according to claim 7 , wherein the characteristics of the distorted time-varying supply voltage comprise at least one of the following: a level of the supply voltage, a phase of the supply voltage and a frequency of the supply voltage.

9. The apparatus according to claim 7 , further comprising a sampling processor configured to:

sample the distorted time-varying supply voltage for a number of predefined time periods at more than one time instant;

subtract a nominal value of a supply voltage characteristic at each time period from the samples at the corresponding time period;

average the samples at corresponding time instants over more than one time period;

generate a model for the distortion introduced to the time-varying supply voltage by the power supply on the basis of the samples; and

estimate the characteristics of the distorted time-varying supply voltage on the basis of the model.

10. The apparatus according to claim 7 , wherein the memory and the computer program code are further configured to, with the processor, cause the apparatus at least to:

take the amplitude of the input signal of the power amplifier into account when determining the at least one correction factor.

11. The apparatus according to claim 7 , wherein the at least one correction factor is an inverse of the distortion on the radio frequency output signal of the power amplifier.

12. The apparatus according to claim 7 , wherein the power supply is a switched mode power supply.

13. A computer-readable storage medium encoded with instructions which, when executed by a computer, performs:

receiving a distorted time-varying supply voltage from a power supply;

determining at least one correction factor for a distortion on a radio frequency output signal of a power amplifier on the basis of estimated characteristics of the distorted time-varying supply voltage; and

applying the at least one correction factor to an input signal of the power amplifier.

14. A computer program product comprising program code encoded on a computer-readable storage medium which, when executed by a computer, performs:

receiving a distorted time-varying supply voltage from a power supply;

determining at least one correction factor for a distortion on a radio frequency output signal of a power amplifier on the basis of estimated characteristics of the distorted time-varying supply voltage; and

applying the at least one correction factor to an input signal of the power amplifier.

15. An apparatus, comprising:

determining means for determining at least one correction factor for a distortion on a radio frequency output signal of a power amplifier on the basis of estimated characteristics of a distorted time-varying supply voltage received from a power supply to a power amplifier; and

interface means for applying the at least one correction factor to an input signal of the power amplifier.

16. The apparatus according to claim 15 , further comprising:

processing means for:

sampling the distorted time-varying supply voltage for a number of predefined time periods at more than one time instant;

subtracting the level of the nominal supply voltage at each time period from the samples at the corresponding time period;

averaging the samples at corresponding time instants over more than one time period;

generating a model for the distortion introduced to the time-varying supply voltage by the power supply on the basis of the samples; and

estimating the characteristics of the distorted time-varying supply voltage on the basis of the model.