Amplifier pre-distortion processing based on composite look-up tables
View Patent ↗Current and previous input signal power measures are used to generate a combined index value that is applied to one or more composite look-up tables (e.g., an I LUT and a Q LUT) to retrieve one or more pre-distortion parameters (e.g., I and Q). In one embodiment, a combined index value is generated by concatenating current and previous power measures, where each composite LUT maps all possible combinations of the current and previous power measures to the corresponding pre distortion parameters values. By using a composite LUT for each of I and Q, the overall signal processing time of the pre-distortion processing can be greatly reduced relative to the prior art, resulting in a significantly smaller RF delay line used to delay the input signal and thereby providing a less costly and more efficient amplifier system.
1. A method for processing an input signal for application to an amplifier to generate an amplified output signal, the method comprising:
generating a measure characterizing previous power of the input signal;
generating a measure characterizing current power of the input signal;
generating a combined index value from the current and previous power measures;
applying the combined index value to one or more look-up tables (LUTs) to retrieve one or more pre-distortion parameters;
applying the one or more pre-distortion parameters to the input signal to generate a pre-distorted input signal for application to the amplifier.
2. The invention of claim 1 , further comprising amplifying the pre-distorted input signal using the amplifier to generate the amplified output signal.
3. The invention of claim 1 , wherein:
the current power measure is a measure of instantaneous envelope power of the input signal; and
the previous power measure is the measure of the instantaneous envelope power of the input signal from a previous processing cycle.
4. The invention of claim 1 , wherein the combined index value corresponds to a concatenation of the current and previous power measures.
5. The invention of claim 4 , wherein each LUT maps all possible combinations of the current and previous power measures.
6. The invention of claim 1 , wherein the combined index value corresponds to a concatenation of the current power measure and a difference between the current and previous power measures.
7. The invention of claim 6 , wherein each LUT maps all possible combinations of the current power measure and the power measure difference.
8. The invention of claim 1 , wherein each LUT is stored in a RAM where the combined index value is applied to each RAM to retrieve one of the one or more pre-distortion parameters.
9. The invention of claim 1 , wherein the one or more LUTs comprises a composite I LUT and a composite Q LUT.
10. The invention of claim 9 , wherein the pre-distorted input signal is generated by applying the input signal and I and Q pre-distortion parameters retrieved from the composite I and Q LUTs to a vector modulator.
11. An apparatus for processing an input signal for application to an amplifier to generate an amplified output signal, the apparatus comprising:
a power detector adapted to generate a measure characterizing power of the input signal;
one or more look-up tables (LUTs) adapted to provide one or more pre-distortion parameters, wherein each LUT is adapted to receive a combined index value generated based on a current input signal power measure and a previous input signal power measure; and
a modulator adapted to apply the one or more pre-distortion parameters to the input signal to generate a pre-distorted input signal for application to the amplifier.
12. The invention of claim 11 , further comprising the amplifier adapted to amplify the pre-distorted input signal to generate the amplified output signal.
13. The invention of claim 11 , wherein the power detector is adapted to measure instantaneous envelope power of the input signal.
14. The invention of claim 13 , further comprising an analog-to-digital converter (ADC) adapted to convert an analog power measure from the power detector into a digital power measure.
15. The invention of claim 14 , wherein the ADC is adapted to output a current digital power measure and a previous digital power measure at every operating cycle.
16. The invention of claim 11 , wherein the combined index value corresponds to a concatenation of the current and previous power measures.
17. The invention of claim 16 , wherein each LUT maps all possible combinations of the current and previous power measures.
18. The invention of claim 11 , wherein the combined index value corresponds to a concatenation of the current power measure and a difference between the current and previous power measures.
19. The invention of claim 18 , wherein each LUT maps all possible combinations of the current power measure and the power measure difference.
20. The invention of claim 11 , wherein each LUT is stored in a RAM where the combined index value is applied to each RAM to retrieve one of the one or more pre-distortion parameters.
21. The invention of claim 1 , wherein the one or more LUTs comprises a composite I LUT and a composite Q LUT.
22. The invention of claim 21 , wherein the modulator is a vector modulator adapted to apply I and Q pre-distortion parameters retrieved from the composite I and Q LUTs to the input signal to generate the pre-distorted input signal.
23. The invention of claim 11 , wherein:
the power detector is adapted to measure instantaneous envelope power of the input signal;
further comprising an analog-to-digital converter (ADC) adapted to convert an analog power measure from the power detector into a digital power measure, wherein the ADC is adapted to output a current digital power measure and a previous digital power measure at every operating cycle;
the combined index value corresponds to a concatenation of the current and previous power measures;
each LUT maps all possible combinations of the current and previous power measures;
each LUT is stored in a RAM where the combined index value is applied to each RAM to retrieve one of the one or more pre-distortion parameters;
the one or more LUTs comprises a composite I LUT and a composite Q LUT; and
the modulator is a vector modulator adapted to apply I and Q pre-distortion parameters retrieved from the composite I and Q LUTs to the input signal to generate the pre-distorted input signal.
24. The invention of claim 23 , further comprising the amplifier adapted to amplify the pre-distorted input signal to generate the amplified output signal.