High dynamic range AMAM predistortion

1. An apparatus to receive a plurality of input in-phase (I) and quadrature (Q) data words provided from respective I and Q data channels, the apparatus comprising:

a digital power amplifier configured to generate a radio-frequency (RF) analog signal in accordance with a sequence of predistorted digital I and Q data words generated from the respective input I and Q data words and configured to generate maximum current when an input data word provided thereto is a full scale value; and

a predistortion processor, comprising:

a multiplicative stage to evaluate a predetermined predistortion function with each of the input I and Q data words as arguments to generate computed I and Q data words;

an additive stage to respectively generate additive I and Q data words, wherein the additive stage comprises a lookup table stored in a memory and containing the additive I and Q data words indexed by the respective input I and Q data words; and

an adder to add the additive I and Q data words to the respective computed I and Q data words to produce corresponding predistorted I and Q data words that compose the sequence of predistorted digital I and Q words used to generate the RF analog signal.

2. The apparatus of claim 1 , wherein the multiplicative stage generates the computed I and Q data words to be substantially equal to the corresponding predistorted I and Q data words when the input I and Q data words are less than a predetermined threshold.

3. The apparatus of claim 2 , wherein the additive stage generates the additive I and Q data words as non-zero values when the respective values of the input I and Q data words are greater than the predetermined threshold.

4. The apparatus of claim 2 , wherein the multiplicative stage generates the computed I and Q data words to be less than the corresponding predistorted I and Q data words when the input I and Q data words are greater than the predetermined threshold.

5. The apparatus of claim 4 , wherein the additive stage generates the additive I and Q data words as respective differences between the computed I and Q data words and the respective predistorted I and Q data words when the respective values of the input I and Q data words are greater than the predetermined threshold.

6. The apparatus of claim 4 , wherein the multiplicative stage comprises a polynomial processor to generate the computed I and Q data words in accordance with a polynomial as the predistortion function.

7. The apparatus of claim 6 , wherein the polynomial implemented by the polynomial processor is of polynomial order no greater than five (5).

8. The apparatus of claim 1 , wherein the additive stage further comprises an interpolator to interpolate between the additive I and Q data words stored in the lookup table to generate an additive data word from neighboring additive data words.

9. A method comprising:

generating each of computed in-phase (I) and quadrature (Q) data words in accordance with a predetermined predistortion function evaluated with input I and Q data words as arguments;

generating additive I and Q data words, wherein generating the additive I and Q data words comprises retrieving the additive I and Q data words from a lookup table stored in a memory at indexes corresponding to the respective input I and Q data words;

adding the additive I and Q data words to the respective computed I and Q data words to produce corresponding predistorted I and Q data words; and

providing a sequence of the predistorted I and Q data words to the digital power amplifier to generate a radio-frequency analog signal converted therefrom.

10. The method of claim 9 , wherein generating the computed I and Q data words comprises defining the predetermined predistortion function to evaluate substantially equal to the corresponding predistorted I and Q data words when the input I and Q data words are less than a predetermined threshold.

11. The method of claim 10 , wherein generating the additive I and Q data words comprises generating the additive I and Q data words as non-zero values when the respective values of the input I and Q data words are greater than the predetermined threshold.

12. The method of claim 10 , wherein generating the computed I and Q data words comprises defining the predetermined predistortion function to evaluate to less than the predistorted I and Q data words when the input I and Q data words used as arguments are greater than the predetermined threshold.

13. The method of claim 12 , wherein generating the additive I and Q data words comprises generating the additive I and Q data words as respective differences between the computed I and Q data words and the respective predistorted I and Q data words when the respective values of the input I and Q data words are greater than the predetermined threshold.

14. The method of claim 12 , wherein generating the computed I and Q data words comprises generating the computed I and Q data words in accordance with a polynomial.

15. A tangible non-transient computer readable medium having encoded thereon processor instructions that, when executed by a processor, configures the processor to:

generate each of computed in-phase (I) and quadrature (Q) data words in accordance with a predetermined predistortion function evaluated with input I and Q data words as arguments;

generate additive I and Q data words, by retrieving the additive I and Q data words from a lookup table stored in a memory at indexes corresponding to the respective input I and Q data words;

add the additive I and Q data words to the respective computed I and Q data words to produce corresponding predistorted I and Q data words; and

provide a sequence of the predistorted digital I and Q data words to the digital power amplifier to generate a radio-frequency analog signal converted therefrom.

16. The computer readable medium of claim 15 having instructions encoded thereon that configure the processor to generate the computed I and Q data words in accordance with a polynomial as the predetermined predistortion function.

17. The computer readable medium of claim 15 having instructions encoded thereon to configure the processor to store in the lookup table the additive I and Q data words as substantially equal to respective differences between the computed I and Q data words and the respective predistorted I and Q data words for values of the input I and Q data words that are greater than the predetermined threshold.