Time alignment for an amplification stage

1. A method of calibrating a polar amplification stage including a main signal path and a magnitude signal path, the method comprising:

generating signals for the main signal path and the magnitude signal path for operating an amplifier between a linear mode of operation and a saturated mode of operation;

detecting first and second peaks in a signal at an output of the amplifier representing transitions between the linear and saturated modes of operation; and

adjusting a timing in one of the main signal path and the magnitude signal path in dependence on a relative difference between the size of the detected first and second peaks.

2. The method of claim 1 wherein operating the amplifier between the linear and saturated modes of operation comprises switching the operating mode of the amplifier from the linear or saturated mode to the saturation or linear mode respectively, and back.

3. The method of claim 1 wherein generating the signals for the main signal path and the magnitude signal path comprises:

generating an input signal for the main signal path to the amplifier having rising and falling slopes; and

generating an input signal for the magnitude signal path to the amplifier having opposite slopes to the signal in the main signal path.

4. The method of claim 3 wherein the input signal in the main signal path includes a rising slope followed by a falling slope, the first peak in the output signal corresponding to a condition where the amplifier transitions from the linear mode of operation to the saturated mode of operation, and the second peak in the output signal corresponding to a condition where the amplifier transitions from the saturated mode of operation to the linear mode of operation.

5. The method of claim 1 wherein if the first peak is determined to be larger than the second peak, the timing of the magnitude signal path is delayed relative to the timing of the main signal path.

6. The method of claim 1 wherein if the first peak is determined to be smaller than the second peak, the timing of the main signal path is delayed relative to the timing of the magnitude signal path.

7. The method of claim 1 wherein the signals are periodic, and the generating, the detecting, and the adjusting are repeated for each period.

8. The method of claim 1 wherein the generating, the detecting, and the adjusting are performed for a calibration phase of operation and wherein the timing is adjusted prior to a normal phase of operation.

9. The method of claim 1 wherein the polar amplification stage is an envelope tracking modulator, the magnitude signal path comprising an envelope signal path and the main signal path comprising a path of a signal to be amplified.

10. The method of claim 1 wherein the amplification stage is an RF amplification stage.

11. A polar amplification stage including a main signal path to an amplifier input and a magnitude signal path to a supply of an amplifier, the polar amplification stage further comprising:

a signal generator for generating signals for the main signal path and the magnitude signal path arranged to operate the amplifier between a linear mode of operation and a saturated mode of operation;

a detector for detecting first and second peaks in a signal at an output of the amplifier representing transitions between the linear and saturated modes of operation; and

a delay adjustment block for adjusting a timing in one of the main signal path and the magnitude signal path in dependence on a relative difference between the size of the detected first and second peaks.

12. The polar amplification stage of claim 11 wherein the signal generator is arranged to generate the signals to operate the amplifier between the linear and saturated modes of operation by switching the operating mode of the amplifier from the linear or saturated mode to the saturation or linear mode respectively, and back.

13. The polar amplification stage of claim 11 wherein the signal generator is arranged to:

generate an input signal for the main signal path to the amplifier having rising and falling slopes; and

generate an input signal for the magnitude signal path to the amplifier having opposite slopes to the signal in the main signal path.

14. The polar amplification stage of claim 13 wherein the signal generator is arranged to generate the signals such that the input signal in the main signal path includes a rising slope followed by a falling slope, the first peak in the output signal corresponding to a condition where the amplifier transitions from the linear mode of operation to the saturated mode of operation, and the second peak in the output signal corresponding to a condition where the amplifier transitions from the saturated mode of operation to the linear mode of operation.

15. The polar amplification stage of claim 11 wherein the adjustment bock is arranged such that if the first peak is determined to be larger than the second peak, the timing of the magnitude signal path is delayed relative to the timing of the main signal path.

16. The polar amplification stage of claim 11 wherein the adjustment block is arranged such that if the first peak is determined to be smaller than the second peak, the timing of the main signal path is delayed relative to the timing of the magnitude signal path.

17. The polar amplification stage of claim 11 wherein the signal generator is arranged to generate periodic input signals.

18. The polar amplification stage of claim 11 wherein the adjustment block is arranged to adjust the timing prior to a normal phase of operation.

19. The polar amplification stage of claim 11 wherein the polar amplification stage is an envelope tracking modulator, the magnitude signal path comprising an envelope signal path and the main signal path comprising a path of a signal to be amplified.

20. The polar amplification stage of claim 11 wherein the amplification stage is an RF amplification stage.