System and method for digital memorized predistortion for wireless communication

1. A power amplifier system comprising:

an input operable to receive a signal that reflects information to be communicated;

an address data former operable to generate a digital lookup table key;

a predistortion lookup table coupled to the address data former;

a power amplifier having an output and an input, wherein the input to the power amplifier is coupled to the predistortion lookup table;

a feedback signal representing the output of the power amplifier; and

a switch coupled to the feedback signal and the predistortion lookup table, wherein the switch is configured to disconnect the feedback signal from the predistortion lookup table.

2. The power amplifier system of claim 1 , wherein the power amplifier system is a component of a mobile device.

3. The power amplifier system of claim 1 , wherein the power amplifier system is a component of a base station.

4. The power amplifier system of claim 1 , wherein the switch couples the feedback signal and the predistortion lookup table during a training phase, and wherein the switch decouples the feedback signal and the predistortion lookup table during an operating phase.

5. A predistorter, comprising:

an address data former;

a linearity and time-delay lookup table coupled to the address data former;

a predistortion lookup table coupled to the address data former;

a vector multiplier coupled to an output of the predistortion lookup table;

an error comparator coupled to an output of the linearity and time-delay lookup table and an input of the predistortion lookup table;

a status switch; and

an on/off switch.

6. The predistorter of claim 5 , wherein the address data former is configured to accept coded in-phase and quadrature symbols, wherein the coded in-phase and quadrature symbols represent information that is to be communicated.

7. The predistorter of claim 5 , wherein the address data former is configured to provide an address to both the linearity and time-delay lookup table and the predistortion lookup table.

8. The predistorter of claim 5 , wherein the linearity and time-delay lookup table is used to store linearity characteristics of a power amplifier and time-delay characteristics of a channel from an output of the power amplifier to the error comparator.

9. The predistorter of claim 5 , wherein the predistortion lookup table is used to store predistortion signals to linearize a power amplifier.

10. The predistorter of claim 9 , wherein the predistortion signals are obtained by comparing signals from the linearity and time-delay lookup table and feedback signals representing the output of the power amplifier.

11. The predistorter of claim 5 , wherein the on/off switch couples the error comparator and the predistortion lookup table during a training phase.

12. The predistorter of claim 5 , wherein the status switch enables the linearity and time-delay lookup table and the predistortion lookup table to be adaptively updated during a training phase.

13. A method for operating a power amplifier, the method comprising:

initializing the power amplifier, wherein initializing includes setting a switch to connect an output of the power amplifier to a training circuit; and

executing a training procedure, wherein the training procedure includes:

determining a pre-computed distortion contribution associated with a feedback signal representative of an output of the power amplifier, wherein the feedback signal includes a nonlinear distortion component; and

storing the pre-computed distortion contribution in a lookup table.

14. The method of claim 13 , further comprising:

executing an operating phase, wherein the operating phase includes:

setting the switch to disconnect the output of the power amplifier from the training circuit;

accepting an original value that reflects information to be communicated;

generating a digital lookup table key using the original value;

retrieving, using the digital lookup table key, a pre-computed distortion contribution from the lookup table, wherein the pre-computed distortion contribution corresponds to the original value;

distorting the original value using the pre-computed distortion contribution to obtain a distorted value; wherein distorting the original value pre-compensates for nonlinear characteristics of the power amplifier;

generating a pre-distorted signal using the original value and the distorted value; and

wirelessly transmitting a pre-distorted signal.

15. The method of claim 14 , wherein the power amplifier is a component of a mobile device.

16. The method of claim 15 , wherein the operating phase lasts for at least one entire telephone conversation.

17. The method of claim 14 , wherein the power amplifier is a component of a base station.

18. The method of claim 13 , wherein determining a pre-computed distortion contribution includes:

determining reference information, wherein the reference information is determined by training, wherein the training uses reference training feedback signals, wherein the reference training feedback signals are representative of the output of the power amplifier; and

storing the reference information in a reference table.

19. The method of claim 18 , wherein determining a pre-computed distortion contribution includes:

squaring an in-phase component of the feedback signal to produce a squared in-phase output value;

squaring a quadrature component of the feedback signal to produce a squared quadrature output value;

squaring an in-phase component of a reference signal to produce a squared in-phase reference value, wherein the reference signal is derived from the reference information;

squaring a quadrature component of the reference signal to produce a squared quadrature reference value;

determining an in-phase difference between the squared in-phase reference value and the squared in-phase output value;

determining a quadrature difference between the squared quadrature reference value and the squared quadrature output value; and

determining the pre-computed distortion contribution based on the in-phase difference and the quadrature difference.

20. The method of claim 18 , wherein the reference information represents linearity characteristics of the power amplifier and time-delay parameters of the feedback signals.