Technique for Generating a Radio Frequency Signal Based on a Peak or an Offset Compensation Signal

• US 20140016723A1
• Filed: 07/11/2013
• Published: 01/16/2014
• Est. Priority Date: 07/11/2012
• Status: Abandoned Application

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Mu, Fenghao, Sundstrm, Lars
• Application Number:
  US13/939,795
• Publication Number:
  US 20140016723A1
• Time in Patent Office: Days
• US Class Current: 375/296
• CPC Class Codes: H04B 1/62 for providing a predistortion of the signal in the transmitter and corresponding correction in the receiver, e.g. for improving the signal/noise ratio
• CPC Class Codes: H04L 27/3411 reducing the peak to average power ratio or the mean power of the constellation; Arrangements for increasing the shape gain of a signal set
• CPC Class Codes: H04L 27/361 Modulation using a single or unspecified number of carriers, e.g. with separate stages of phase and amplitude modulation
• CPC Class Codes: H04L 27/364 Arrangements for overcoming imperfections in the modulator, e.g. quadrature error or unbalanced I and Q levels
• CPC Class Codes: H04W 52/52 using AGC [Automatic Gain Control] circuits or amplifiers

Abstract

A technique for generating a radio frequency signal (302) based on a baseband signal (304) is provided. As to a method aspect of the technique, an amplitude signal (r) and a phase signal (φ) depending on the baseband signal (304) are provided. The phase signal is modulated to a carrier frequency. As to another method aspect of the technique, a baseband signal (304) is modified by adding an offset signal to the baseband signal (304). The offset signal prevents the modified baseband signal (316) from entering a first signal region. An amplitude signal (r) and a phase signal (φ) is provided based on the modified baseband signal (316). The phase signal (φ) is modulated to a carrier frequency (ω_c). The modulated phase signal (φ) is amplified according to the amplitude signal (r) to generate a preliminary radio frequency signal (318). A peak compensation signal (321), which depends on the baseband signal (304), or an offset compensation signal (320) derived from the offset signal (314), is fed into the preliminary radio frequency signal (318) to generate the radio frequency signal (302).

Claims

1. A method of generating a radio frequency signal based on a baseband signal, the method comprising:

modifying the baseband signal by adding an offset signal to the baseband signal, the offset signal being configured to prevent the modified baseband signal from entering a first signal region;

providing an amplitude signal and a phase signal based on the modified baseband signal;

modulating the phase signal to a carrier frequency and amplifying the modulated phase signal according to the amplitude signal to generate a preliminary radio frequency signal; and

feeding an offset compensation signal derived from the offset signal into the preliminary radio frequency signal to generate the radio frequency signal, wherein the offset compensation signal is configured to at least essentially cancel a distortion component, which corresponds to the offset signal, in the preliminary radio frequency signal.

2. The method of claim 1, wherein the modification step is performed and the offset compensation signal is derived from the offset signal, if the baseband signal is in a second signal region, wherein a minimum amplitude defines an upper limit of the first signal region and an activation amplitude defines an upper limit of the second signal region.

3. The method of claim 1, wherein at least one of the first signal region and the second signal region changes depending on an output signal level of the radio frequency signal and/or a modulation scheme applied for the baseband signal.

4. The method of claim 1, wherein at least one of the modulation and the amplification is performed by operating a component in a non-linear mode or in a switched mode.

5. The method of claim 4, wherein the amplitude signal depends on the baseband signal such that the radio frequency signal is at least essentially a linear frequency translation of the baseband signal.

6. The method of claim 1, wherein essentially no offset signal is added, if the baseband signal is in a third signal region.

7. The method of claim 1, further comprising:

feeding a peak compensation signal derived from the baseband signal into the preliminary radio frequency signal, wherein the peak compensation signal at least essentially compensates for a saturation in the amplification, if the baseband signal is in a fourth signal region or a fifth signal region.

8. The method of claim 7, wherein feeding the peak compensation signal into the preliminary radio frequency signal further includes a weighted combination of the peak compensation signal and the preliminary radio frequency signal.

9. The method of claim 8, further comprising:

statically or dynamically calibrating one or more weight coefficients of the weighted combination.

10. The method of claim 7, wherein a saturation amplitude is at least one of an upper limit of the third signal region and a lower limit of the fourth signal region.

11. The method of claim 7, wherein the peak compensation signal increases as a function of the baseband signal, if the baseband signal is in the fifth signal region.

12. The method of claim 7, wherein a clipping amplitude defines a lower limit of the fifth signal region.

13. The method of claim 7, wherein the peak compensation signal is further configured to modify the preliminary radio frequency signal so that an approach to the lower limit of the fifth signal region has a predefined transition time.

14. The method of claim 7, wherein the offset compensation signal and the peak compensation signal are generated by an auxiliary power amplifier and the phase signal is applied to the auxiliary power amplifier in at least one of the fourth signal region and the fifth signal region.

15. The method of claim 14, wherein the auxiliary power amplifier may be a polar-modulated auxiliary power amplifier or a quadrature-modulated auxiliary power amplifier.

16. The method of claim 1, wherein the deriving of the offset compensation signal includes aligning the offset compensation signal relative to the preliminary radio frequency signal according to an alignment setting, the method further comprising:

generating a calibration signal, which substitutes the offset signal and from which the offset compensation signal is derived according to the alignment setting;

detecting a component, which corresponds to the calibration signal, in the radio frequency signal; and

calibrating the alignment setting, wherein the calibration aims at reducing the detected component.

17. A method of generating a radio frequency signal based on a baseband signal, the method comprising:

providing an amplitude signal and a phase signal depending on the baseband signal;

modulating the phase signal to a carrier frequency and amplifying the modulated phase signal according to the amplitude signal to generate a preliminary radio frequency signal using a main modulating and amplifying circuit; and

feeding a peak compensation signal, which depends on the baseband signal, into the preliminary radio frequency signal to generate the radio frequency signal, the peak compensation signal being generated using an auxiliary modulating and amplifying circuit and configured to at least essentially compensate for a saturation in the main modulating and amplifying circuit, wherein the auxiliary modulating and amplifying circuit is further used for feeding an offset compensation signal into the preliminary radio frequency signal, when the baseband signal is modified to reduce a bandwidth expansion in at least one of the phase signal and the amplitude signal.

18. The method of claim 17, wherein the peak compensation signal increases as the amplitude signal increases, if the baseband signal is in at least one of a first signal region and a second signal region, so that an amplitude of the radio frequency signal is a linear function of an amplitude of the baseband signal.

19. The method of claim 18, further comprising:

determining whether the baseband signal is in the first signal region or the second signal region, or predicting whether the baseband signal enters into the first signal region or the second signal region based on the baseband signal stored in a transmitter.

20. The method of claim 18, wherein at least the feeding of the peak compensation signal is subject to the condition that the baseband signal is in the first signal region or the second signal region.

21. The method of claim 17, wherein the feeding of the peak compensation signal into the preliminary radio frequency signal further includes a calibrated combination of the peak compensation signal and the preliminary radio frequency signal.

22. The method of claim 21, wherein the calibrated combination is based on one or more weight coefficients, the method further comprising:

statically or dynamically calibrating one or all of the weight coefficients so that a signal amplitude provided by each of the auxiliary modulating and amplifying circuit and the main modulating and amplifying circuit is a smooth function of time.

23. The method of claim 18, wherein the peak compensation signal is further configured to modify the preliminary radio frequency signal so that the radio frequency signal approaches a first output signal region corresponding to the first signal region from a second output signal region corresponding to the second signal region with a transition time of the radio frequency signal that is longer than a transition time of the preliminary radio frequency signal.

24. The method of claim 17, further comprising:

determining or predicting whether the baseband signal is in a fourth signal region or enters into the fourth signal region.

25. The method of claim 24, further comprising, if the baseband signal is in the fourth signal region:

modifying the baseband signal by adding an offset signal to the baseband signal, the offset signal being configured to prevent the modified baseband signal from entering a fifth signal region; and

feeding an offset compensation signal derived from the offset signal into the preliminary radio frequency signal using the auxiliary modulating and amplifying circuit, wherein the offset compensation signal is configured to at least essentially cancel a distortion component, which corresponds to the offset signal.

26. The method of claim 24, wherein at least one of the fourth signal region and the fifth signal region changes depending on an output signal level of the radio frequency signal and/or a modulation scheme applied for the baseband signal.

27. The method of claim 24, wherein the offset compensation signal and the peak compensation signal are generated by an auxiliary power amplifier, and wherein the phase signal is applied to the auxiliary power amplifier in at least one of the first signal region and the second signal region for peak compensation, and a phase signal opposite to the offset signal is applied to the auxiliary power amplifier in at least one of the fourth signal region and the fifth signal region for offset compensation.

28. The method of claim 27, wherein the auxiliary power amplifier is a polar-modulated auxiliary power amplifier or a quadrature-modulated auxiliary power amplifier.

29. The method of claim 17, wherein at least one of the modulation and the amplification is performed by operating a component in a non-linear mode or in a switched mode.

30. The method of claim 17, wherein the deriving of the peak compensation signal includes aligning the peak compensation signal relative to the preliminary radio frequency signal according to an alignment setting.

31. The method of claim 17, wherein the peak compensation signal, the offset compensation signal or another compensation signal, which is generated by the auxiliary modulating and amplifying circuit, is configured to compensate a distortion in the preliminary radio frequency signal created by the main modulating and amplifying circuit or in a main power amplifier path including or downstream of the main modulating and amplifying circuit.

32. A device for generating a radio frequency signal based on a baseband signal, the device comprising:

a providing circuit adapted to provide an amplitude signal and a phase signal depending on the baseband signal;

a main modulating and amplifying circuit adapted to modulate the phase signal to a carrier frequency and to amplify the modulated phase signal according to the amplitude signal to generate a preliminary radio frequency signal; and

a feeding circuit adapted to feed a peak compensation signal, which depends on the baseband signal, into the preliminary radio frequency signal to generate the radio frequency signal, wherein the feeding circuit includes an auxiliary modulating and amplifying circuit adapted to generate the peak compensation signal configured to at least essentially compensate for a saturation in the main modulating and amplifying circuit, wherein the feeding circuit is further adapted to feed an offset compensation signal generated by the auxiliary modulating and amplifying circuit into the preliminary radio frequency signal, when the baseband signal is modified to reduce a bandwidth expansion in at least one of the phase signal and the amplitude signal.

33. A device for generating a radio frequency signal based on a baseband signal the device comprising:

a modifying circuit adapted to modify the baseband signal by adding an offset signal to the baseband signal, the offset signal being configured to prevent the modified baseband signal from entering a first signal region;

a providing circuit adapted to provide an amplitude signal and a phase signal based on the modified baseband signal;

a modulating and amplifying circuit adapted to modulate the phase signal to a carrier frequency and to amplify the modulated phase signal according to the amplitude signal to generate a preliminary radio frequency signal; and

a feeding circuit adapted to feed an offset compensation signal derived from the offset signal into the preliminary radio frequency signal to generate the radio frequency signal, wherein the offset compensation signal is configured to at least essentially cancel a distortion component, which corresponds to the offset signal, in the preliminary radio frequency signal.

34. The device of claim 33, wherein the modifying circuit is activated and/or the offset compensation signal is derived from the offset signal, if the baseband signal enters a second signal region.

35. The device of claim 33, wherein the feeding circuit is at least essentially deactivated, if the baseband signal is in a third signal region.

36. The device of claim 33, wherein the feeding circuit is further adapted to feed a peak compensation signal derived from the baseband signal into the preliminary radio frequency signal, wherein the peak compensation signal at least essentially compensates for a saturation in the amplification, if the baseband signal is in a fourth signal region or a fifth signal region.

37. The device of claim 33, wherein the feeding circuit includes an alignment circuit adapted to align the offset compensation signal relative to the preliminary radio frequency signal according to an alignment setting, the device further comprising:

a generating circuit adapted to generate a calibration signal, which substitutes the offset signal and from which the offset compensation signal is derived according to the alignment setting;

a detecting circuit adapted to detect a component, which corresponds to the calibration signal, in the radio frequency signal; and

a calibrating circuit adapted to calibrate the alignment setting, wherein the calibration aims at reducing the detected component.