Method of power amplifier calibration for an envelope tracking system

1. A method for power amplifier (PA) calibration for an envelope tracking system of a wireless device comprising:

measuring an output power of a PA that is a part under test (PUT) at a predetermined input power;

calculating a gain equal to the output power of the PA divided by the predetermined input power;

calculating a gain correction by subtracting the calculated gain from a desired gain;

determining an expected supply voltage for the PA at the desired gain using the gain correction applied to a nominal curve of gain versus PA supply voltage;

determining a first difference between a measured PA supply voltage and a nominal PA supply voltage value for a first input power;

determining a second difference between a measured PA supply voltage and a nominal PA supply voltage value for a second input power;

calculating a slope and an intercept for a line that that yields calibration values as a function of PA supply voltage using the first difference, the second difference, the first input power, and the second input power; and

storing the calibration values for PA supply voltage versus input power in a look up table memory that is accessible by the wireless device.

2. The method of claim 1 further including steps comprising:

determining a third difference between a measured PA supply voltage and a nominal PA supply voltage value for a third input power;

calculating a second slope and a second intercept for a second line that that yields calibration values as a function of PA supply voltage using the second difference, the third difference, the second input power, and the third input power; and

storing the calibration values for PA supply voltage versus input power in a look up table memory that is accessible by the wireless device.

3. The method of claim 1 wherein calculating the slope is performed by a calibration system having a processor that divides the second difference minus the first difference by the second input power minus the first input power.

4. The method of claim 1 wherein the intercept is equal to the first difference.

5. The method of claim 2 wherein calculating the second slope is performed by a calibration system having a processor that divides the third difference minus the second difference by the third input power minus the second input power.

6. The method of claim 2 wherein the intercept is equal to the second difference.

7. A calibration system for calibrating a PA for an envelope tracking system of a wireless device comprising:

a memory to store an expected supply voltage of the PA;

a processor programmed to:

measure an output power of a PA that is a part under test (PUT) at a predetermined input power;

calculate a gain equal to the output power of the PA divided by the predetermined input power;

calculate a gain correction by subtracting the calculated gain from a desired gain; and

determine an expected supply voltage for the PA at the desired gain using the gain correction applied to a nominal curve of gain versus PA supply voltage;

determine a first difference between a measured PA supply voltage and a nominal PA supply voltage value for a first input power;

determine a second difference between a measured PA supply voltage and a nominal PA supply voltage value for a second input power;

calculate a slope and an intercept for a line that that yields calibration values as a function of PA supply voltage using the first difference, the second difference, the first input power, and the second input power; and

store the calibration values for PA supply voltage versus input power in a look up table memory that is accessible by the wireless device.

8. The calibration system of claim 7 wherein the processor of the calibration system is further programmed to:

determine a third difference between a measured PA supply voltage and a nominal PA supply voltage value for a third input power;

calculate a second slope and a second intercept for a second line that that yields calibration values as a function of PA supply voltage using the second difference, the third difference, the second input power, and the third input power; and

store the calibration values for PA supply voltage versus input power in a look up table memory that is accessible by the wireless device.

9. The calibration system of claim 7 wherein calculating the slope is performed by the processor that is programmed to divide the second difference minus the first difference by the second input power minus the first input power.

10. The calibration system of claim 7 wherein the intercept is equal to the first difference.

11. The calibration system of claim 8 wherein calculating the second slope is performed by the processor that is programmed to divide the third difference minus the second difference by the third input power minus the second input power.

12. The calibration system of claim 8 wherein the intercept is equal to the second difference.

13. A method for power amplifier (PA) calibration for an envelope tracking system of a wireless device comprising:

measuring an output power of a PA that is a part under test (PUT) at a predetermined input power;

calculating a gain equal to the output power of the PA divided by the predetermined input power;

calculating a gain correction by subtracting the calculated gain from a desired gain;

determining an expected supply voltage for the PA at the desired gain using the gain correction applied to a nominal curve of gain versus PA supply voltage;

storing the expected supply voltage for the PA versus input power in memory;

repeating the method steps until N expected supply voltages for the PA are stored;

determining an N difference between an expected PA supply voltage and a nominal PA supply voltage value for an N input power;

determining an N+1 difference between a measured PA supply voltage and a nominal PA supply voltage value for an N+1 input power;

calculating a slope and an intercept for a line that that yields calibration values as a function of PA supply voltage using the N difference, the N+1 difference, the N input power, the N+1 input power, and a nominal PA supply voltage for the N input power; and

storing the calibration values for PA supply voltage versus input power in a look up table memory that is accessible by the wireless device.

14. The method of claim 13 wherein the slope is calculated by dividing the N+1 difference minus the N difference by the N+1 input power minus the N input power.

15. The method of claim 14 wherein the intercept is equal to the N difference.

16. The method of claim 13 wherein the expected supply voltages are interpolated between the N input power and the N+1 input power.

17. The method of claim 13 wherein the expected supply voltages are extrapolated beyond the N input power and the N+1 input power.