Predistortion linearizer for power amplifier

• US 6,337,599 B2
• Filed: 01/02/2001
• Issued: 01/08/2002
• Est. Priority Date: 12/30/1999
• Status: Expired due to Term

• Current Assignee: LG-Ericsson Company Limited (Telefonaktiebolaget LM Ericsson)
• Original Assignee: LG Electronics, Inc. (LG Corporation)
• Inventors: Lee, Jae Hyuk
• Primary Examiner(s): Pascal, Robert
• Assistant Examiner(s): NGUYEN, KHANH V
• Application Number:
  US09/750,908
• Publication Number:
  US 20010006354A1
• Time in Patent Office: 371 Days
• Field of Search: 330/149, 330/136, 330/2, 375/297, 375/296
• US Class Current: 330/149
• CPC Class Codes: H03F 1/3288 to compensate phase shift as a function of the amplitude

Abstract

The present invention relates to a predistortion linearizer for a power amplifier which is capable of improving nonlinear character of a high power amplifier. The predistortion linearizer for the power amplifier includes first and second envelope detectors, which separately detect an envelope of input signals and output signals, respectively, a DSP, which adjusts a tally of a work function by comparing the output signals of the first and the second envelope detector, and a work function generator, which generates a work function from an envelope of input signals to output gain and phase control voltage in accordance with work function tally inputted from the DSP. It also includes a vector modulator, which pre-distorts the input signal in accordance with the control voltages inputted from the work function generator to output a distortion compensation signal to the power amplifier.

Claims

1. A predistortion linearizer for a power amplifier, comprising:

first and second envelope detector circuits configured to detect an envelope of first and second signals, respectively;

a digital signal processor (DSP) coupled to compare output signals of the first and second envelope detector circuits to adjust a tally of a work function;

a work function generator coupled to receive the output signal of the first envelope detector circuit and the work function tally received from the DSP to generate a work function and output at least one control voltage; and

a vector modulator configured to distort the first signal in accordance with the at least one control voltage received from the work function generator and output a distortion compensation signal to a power amplifier.

2. The predistortion linearizer of claim 1, wherein the distortion compensation signal comprises third and fifth elements of −

bx³−

cx⁵.

3. The predistortion linearizer of claim 1, wherein the work function comprises a signal equal to bx²+cx⁴.

4. The predistortion linearizer of claim 1, wherein the first envelope detector circuit comprises a directional coupler configured to sample a portion of the first signal, a delay unit configured to delay the sampled first signal for a prescribed period of time, an envelope detector configured to detect an envelope of the delayed first signal, and a filter configured to pass only a prescribed frequency of the detected envelope as the output signal.

5. The predistortion linearizer of claim 4, wherein the first signal is an input signal to be amplified, and the filter comprises a low-pass filter.

6. The predistortion linearizer or claim 1, wherein the second envelope detector circuit comprises a directional coupler configured to sample a portion of the second signal, a variable attenuator configured to adjust an amplitude of the sampled second signal, an envelope detector configured to detect an envelope of the adjusted second signal, and a filter configured to pass only a prescribed frequency of the detected envelope as the output signal.

7. The predistortion linearizer of claim 6, wherein the second signal is an output signal of the power amplifier and the filter comprises a low-pass filter, and wherein the variable attenuator adjusts the amplitude of the second signal to match an amplitude of the first signal.

8. The predistortion linearizer of claim 1, wherein the DSP comprises a subtracter configured to subtract output signals of the first and second envelope detector circuits, a conjugator configured to change a sign of an imaginary component of the output signal of the first envelope detector, a multiplier coupled to multiply an output of the subtracter by an output of the conjugator, an inverter coupled to invert an output signal of the multiplier, and an integrator coupled to integrate an output of the inverter.

9. The predistortion linearizer of claim 1, wherein the work function generator comprises a first squaring circuit configured to square the output signal of the first envelope detector, a second squaring circuit, coupled to square an output of the first squaring circuit, a first control voltage generator configured to generate a first control voltage based on outputs of the first and second squaring circuits and the tally received from the DSP, and a second control voltage generator configured to generate a second control voltage based on outputs of the first and second squaring circuits and the tally received from the DSP.

10. The predistortion linearizer of claim 9, wherein the first control voltage controls a gain distortion and the second control voltage controls a phase distortion.

11. The predistortion linearizer of claim 9, wherein the first and second control voltage generator comprise a first multiplier configured to multiply the output of the first squaring circuit unit by the tally, a second multiplier configured to multiply the output of the second squaring unit by the tally, and an adder configured to add outputs of the first and second multiplier.

12. The predistortion linearizer of claim 1, wherein the first signal is an input signal to be amplified and the second signal is an output signal from the power amplifier.

13. A predistortion linearizer for a power amplifier, comprising:

first and second envelope detectors configured to detect an envelope of an input signal and an output signal, respectively;

a digital signal processor (DSP) coupled to receive an output of the first and second envelope detectors, adjust a tally of a work function by comparing the output signals, and generate the work function using an output of the first envelope detector and the work function tally to output a gain control voltage and a phase control voltage; and

a vector modulator coupled to receive the gain and phase control voltages and distort the input signal in accordance with the gain and phase control voltages to output a distortion compensation signal to a power amplifier.

14. The predistortion linearizer of claim 13, wherein the DSP comprises a first squaring circuit coupled to square the output of the first envelope detector, a second squaring circuit coupled to square an output of the first squaring circuit, a first control voltage generator coupled to receive outputs of the first and second squaring circuits and the work function tally to generate the gain control voltage, and a second control voltage generator coupled to receive outputs of the first and second squaring circuits and the work function tally to generate the phase control voltage.

15. The predistortion linearizer of claim 14, wherein the distortion compensation signal comprises a signal having third and fifth elements of −

bx³−

cx⁵.

16. The predistortion linearizer of claim 14, wherein the work function WF is represented by the equation WF=bx²+cx⁴.

17. The predistortion linearizer of claim 14, wherein the first envelope detector comprises a directional coupler, which samples the input signal, a delay circuit, which delays the input signal for a prescribed period of time, an envelope detection device, which detects the envelope of the delayed input signal, and a low-pass filter, which passes a low frequency component of the output of the envelope detector.

18. The predistortion linearizer of claim 14, wherein the second envelope detector comprises a directional coupler, which samples the output signal, a variable attenuator, which adjusts an amplitude of the sampled output signal to equal an amplitude of the input signal, an envelope detection device, which detects the envelope of the adjusted output signal, and an low-pass filter, which passes a low frequency component of the output of the envelope detector.

19. The predistortion linearizer of claim 14, wherein the DSP further comprises a subtracter, which subtracts envelope signals detected by the first and second envelope detectors, a conjugator, which changes a sign of an imaginary component of the envelope signal detected by the first envelope detector, a multiplier, which multiplies an output of the subtracter by an output of the conjugator, an inverter, which inverts an output signal of the multiplier, and an integrator, which integrates an output of the inverter to provide the work function tally.

20. A predistortion linearizer for a power amplifier, comprising:

a first squaring circuit, which squares a first envelope signal;

a second squaring circuit, which squares an output of the first squaring circuit;

a first control voltage generator, which generates a first control voltage based on an output of the first squaring circuit, an output of the second squaring circuit, and a tally signal;

a second control voltage generator, which generates a second control voltage based on the output of the first squaring circuit, the output of the second squaring circuit, and the tally signal; and

a vector modulator, which distorts an input signal in accordance with the first and second control voltages to provide a distortion signal as an input to a power amplifier.

21. The predistortion linearizer of claim 20, wherein the distortion compensation signal comprises third and fifth order elements of −

bx³−

cx⁵.

22. The predistortion linearizer of claim 21, wherein the first and second control voltage generators each comprise a first multiplier to multiply the output of the first squaring circuit by the tally signal, a second multiplier to multiply the output of the second squaring circuit by the tally signal, and an adder to add outputs of the first and second multipliers.

23. The predistortion linearizer of claim 20, further comprising a digital signal processor (DSP), which adjusts a tally of a work function by comparing the first envelope signal to a second envelope signal, and outputs the tally signal.

24. The predistortion linearizer of claim 23, wherein the DSP comprises a subtracter to subtract the first envelope signal from the second envelope signal, a conjugator to reverses a sign of an imaginary part of the first envelope signal, a multiplier to multiply an output of the subtracter by an output of the conjugator, an inverter to reverse an output signal of the multiplier, and an integrator to integrate an output of the inverter.

25. The predistortion linearizer of claim 24, wherein the first envelope signal is an envelope of a signal to be amplified by the power amplifier, and the second envelope signal is an envelope of an output signal of the power amplifier.

26. The predistortion linearizer of claim 20, further comprising:

a first envelope detector configured to detect an envelope of an input signal and output the first envelope signal;

a second envelope detector configured to detect an envelope of an output signal of the power amplifier and output the second envelope signal; and

a digital signal processor, configured to receive the first and second envelope signals to generate the tally signal.

27. The predistortion linearizer of claim 26, wherein the input signal is a signal to be amplified by the power amplifier, and the output signal is an amplified input signal.

28. The predistortion linearizer of claim 20, wherein the first control voltage controls a gain distortion of the power amplifier, and the second control voltage controls a phase distortion of the power amplifier.

29. The predistortion linearizer of claim 20, wherein the tally signal comprises an integrated inverse signal, wherein the inverse signal comprises a negative of a product of a difference of the first envelope signal minus the second envelope signal multiplied by a conjugated first envelope signal.

30. A method of generating a predistortion signal for a power amplifier, comprising:

detecting an envelope of first and second signals;

comparing a first detected envelope with a second detected envelope to generate a tally of a work function;

generating a work function using the output of the first envelope detector and the work function tally;

generating first and second control voltages in accordance with the work function;

distorting the first signal by vector modulating the first signal with the first and second control voltages.

31. The method of claim 30, wherein the first control voltage controls a gain distortion of the power amplifier, and wherein the second control voltage controls a phase distortion of the power amplifier.

32. The method of claim 30, wherein the first signal is an input signal to be amplified by the power amplifier, and wherein the second signal is an amplified input signal.