Envelope Tracking (ET) Closed-Loop On-the-Fly Calibration

• US 20160249300A1
• Filed: 02/19/2015
• Published: 08/25/2016
• Est. Priority Date: 02/19/2015
• Status: Active Grant

• Current Assignee: MediaTek, Inc.
• Original Assignee: MediaTek, Inc.
• Inventors: Tsai, Chiou-Wei, Peng, Chia-Sheng, Yan, Sheng-Hong
• Granted Patent: US 9,998,241 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: H03F 1/02 Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation
• CPC Class Codes: H03F 1/32 Modifications of amplifiers to reduce non-linear distortion by negative feedback H03F1/34
• CPC Class Codes: H04B 17/13 of power amplifiers, e.g. gain or non-linearity

Abstract

Apparatus and methods are provided to calibrate a closed-loop envelop tracking system for a power amplifier of a wireless transmitter using standardized modulation signals. In one novel aspect, a closed-loop adaptive method is used to track changes in PA nonlinearity due to environmental or circuitry changes during operating condition using standardized modulation signals. In one embodiment, the PA supply voltage compensation lookup table (LUT) and/or the phase compensation LUT is updated during normal operation to sustain good linearity and efficiency performance. In another novel aspect, the PA target response is adjusted in response to changes in PA-related system configuration, such as changes in PA bias settings, and/or indicators measured from the transmitter such as changes in impedance or temperature changes for the RF module or the PA module. The PA supply voltage compensation LUT and/or the phase LUT is updated accordingly upon adjustment of the PA target response.

Claims

1. A method comprising:

transmitting a wireless signal in a wireless system by a wireless transmitter with a radio frequency (RF) module utilizing an envelope tracking (ET) adapting a power amplifier (PA) supply voltage with a PA target response;

obtaining a reference signal on-the-fly, wherein the reference signal is a baseband digital signal of the transmitted wireless signal using a modulation signal specified by the wireless system;

obtaining a detection signal on-the-fly through a coupler, wherein the detection signal is a partial feedback from down-sampled PA outputs;

computing a difference between a measured response and the PA target response based on the reference signal and the detection signal; and

adjusting a PA supply voltage compensation look up table (LUT) based on the computed difference to maintain the linearity of the ET.

2. The method of claim 1, further comprising:

computing a difference between a measured phase response and a predefined target phase response based on the phase difference between the reference signal and the detection signal; and

adjusting an AM/PM phase compensation LUT based on the computed phase.

3. The method of claim 1, further comprising:

computing a difference between a measured amplitude response and a target amplitude response; and

adjusting an AM/AM compensation LUT for a digital predistortion process based on the computed amplitude difference.

4. The method of claim 1, further comprising:

monitoring one or more PA-related system configuration changes; and

adjusting the PA target response based on the one or more changes of PA-related system configuration.

5. The method of claim 4, further comprising:

updating the PA supply voltage compensation LUT based on the adjusted PA target response.

6. The method of claim 4, further comprising:

updating an AM/PM phase compensation LUT based on the adjusted PA target response.

7. The method of claim 4, further comprising:

updating an AM/AM compensation LUT for a digital predistortion process based on the adjusted PA target response.

8. The method of claim 4, wherein the PA-related system configuration is a PA gate bias setting.

9. The method of claim 1, wherein comprising:

monitoring one or more transmitter indicators measured from the transmitter; and

adjusting the PA target response based on the one or more transmitter indicators.

10. The method of claim 9, further comprising:

updating the PA supply voltage compensation LUT based on the adjusted PA target response.

11. The method of claim 9, further comprising:

updating an AM/PM phase compensation LUT based on the adjusted PA target response.

12. The method of claim 9, further comprising:

updating an AM/AM compensation LUT for a digital predistortion process based on the adjusted PA target response.

13. The method of claim 9, wherein the transmitter indicator is PA impedance.

14. The method of claim 9, wherein transmitter indicators are temperature measures of the PA or the RF module.

15. An apparatus, comprising:

a wireless radio frequency (RF) module that transmits a wireless signal specified in a wireless standard;

a closed-loop envelope tracking (ET) system with a PA target response for a supply voltage of a power amplifier (PA) for the wireless RF module;

an adaptive processing engine that adaptively maintains a linearity of the ET system under operating condition of the PA using modulation signal specified by the wireless standard by updating a PA supply voltage compensation look up table (LUT).

16. The apparatus of claim 15, wherein the adaptive processing engine comprising:

a reference signal detector that obtains a reference signal, wherein the reference signal is a baseband digital signal of the transmitted wireless signal;

a detection signal detector that obtains a detection signal through a coupler, wherein the detection signal is a partial feedback from down-sampled PA outputs;

a difference calculator that computes a difference between a measured response and the PA target response based on the reference signal and the detection signal; and

a PA supply voltage LUT module that adjusts the PA supply voltage compensation LUT based on the computed difference.

17. The apparatus of claim 16, wherein the adaptive processing engine further comprising:

a phase calculator that computes a difference between a measured phase and a predefined target phase based on the phase difference between the reference signal and the detection signal; and

a phase LUT module that adjusts an amplitude-modulation (AM)/phase-modulation (PM) phase compensation LUT based on the computed phase difference to maintain the linearity of the ET.

18. The apparatus of claim 16, further comprising a PA target response module that adjusts the PA target response for the ET system.

19. The apparatus of claim 18, wherein the adjusting the PA target response involves:

monitoring one or more PA-related system configuration changes; and

adjusting the PA target response based on the one or more changes of PA-related system configuration.

20. The apparatus of claim 19, wherein the adjusting the PA target response further involves:

updating the PA supply voltage compensation LUT based on the adjusted PA target response.

21. The apparatus of claim 19, wherein the adjusting the PA target response further involves:

updating an AM/PM phase compensation LUT based on the adjusted PA target response.

22. The apparatus of claim 19, wherein the adjusting the PA target response further involves:

updating an AM/AM compensation LUT for a digital predistortion process based on the adjusted PA target response.

23. The apparatus of claim 19, wherein the PA-related system configuration is a PA gate bias setting.

24. The apparatus of claim 18, wherein the adjusting the PA target response involves:

monitoring one or more transmitter indicators measured from the transmitter;

adjusting the PA target response based on the one or more transmitter indicators.

25. The apparatus of claim 24, wherein the adjusting the PA target response further involves:

updating the PA supply voltage compensation LUT based on the adjusted PA target response.

26. The apparatus of claim 24, wherein the adjusting the PA target response further involves:

updating an AM/PM phase compensation LUT based on the adjusted PA target response.

27. The apparatus of claim 24, wherein the adjusting the PA target response further involves:

updating an AM/AM compensation LUT for a digital predistortion process based on the adjusted PA target response.

28. The apparatus of claim 24, wherein the transmitter indicator is PA impedance.

29. The method of claim 24, wherein transmitter indicators are temperature measures of the PA or the RF module.