Power IQ modulation systems and methods

• US 6,181,199 B1
• Filed: 01/07/1999
• Issued: 01/30/2001
• Est. Priority Date: 01/07/1999
• Status: Expired due to Term

• Current Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Original Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Inventors: Camp, William O. Jr., Dent, Paul W., Holden, Alan R.
• Primary Examiner(s): Pascal, Robert
• Assistant Examiner(s): NGUYEN, KHANH V
• Application Number:
  US09/226,478
• Time in Patent Office: 754 Days
• Field of Search: 330/10, 330/51, 330/124 R, 330/149
• US Class Current: 330/10
• CPC Class Codes: H03C 3/38 by converting amplitude modulation to angle modulation
• CPC Class Codes: H03F 1/3241 using predistortion circuits H03F1/3211, H03F1/3217 take precedence
• CPC Class Codes: H03F 2200/331 Sigma delta modulation being used in an amplifying circuit
• CPC Class Codes: H04L 27/362 Modulation using more than one carrier, e.g. with quadrature carriers, separately amplitude modulated H04L27/366 takes precedence
• CPC Class Codes: H04L 27/367 using predistortion

Abstract

Power IQ modulation systems and methods include first and second power amplifiers, each including a signal input, a supply input and a power input. The first and second power amplifiers are preferably class-C power amplifiers. A source of first, second, third and fourth reference frequency signals is also provided. The first and second reference frequency signals are inverted relative to one another, and the third and fourth reference frequency signals are inverted relative to one another. Preferably, the first, second, third and fourth reference frequency signals are 0°, 180°, 90° and 270° phase shifted reference frequency signals, respectively. A switching system is also provided that selectively applies one of the first and second reference frequency signals to the signal input of the first power amplifier as a function of the polarity of one of the I and Q input signals. The switching system also selectively applies one of the third and fourth reference frequency signals to the signal input of the second power amplifier as a function of the polarity of the other of the I and Q input signals. A third amplifier, preferably a class-D amplifier, is responsive to the one of the I and Q input signals to supply a first variable supply voltage to the supply input of the first amplifier. A fourth amplifier, also preferably a class-D amplifier, is responsive to the other of I and Q input signals to supply a second variable supply voltage to the supply input of the second amplifier. A coupler couples the power outputs of the first and second power amplifiers to a load such as a radiotelephone antenna. Accordingly, power IQ modulation is provided that can use class-C and class-D amplifiers that are highly efficient.

Claims

1. A power modulation system that modulates and amplifies in-phase (I) and quadrature-phase (Q) input signals, the power modulation system comprising:

first and second power amplifiers, each including a signal input, a supply input and a power output;

a source of first, second, third and fourth reference frequency signals, the first and second reference frequency signals being inverted relative to one another and the third and fourth reference frequency signals being inverted relative to one another;

a switching system that selectively applies one of the first and second reference frequency signals to the signal input of the first power amplifier as a function of the polarity of one of the I and Q input signals, and that selectively applies one of the third and fourth reference frequency signals to the signal input of the second power amplifier as a function of the polarity of the other of the I and Q input signals;

a third amplifier that is responsive to the one of the I and Q input signals to supply a first variable supply voltage to the supply input of the first power amplifier;

a fourth amplifier that is responsive to the other of the I and Q input signals to supply a second variable supply voltage to the supply input of the second power amplifier; and

a coupler that couples the power outputs of the first and second power amplifiers to a load.

2. A power modulation system according to claim 1 wherein the first and second power amplifiers comprise class-C power amplifiers and wherein the third and fourth amplifiers comprise class-D power amplifiers.

3. A power modulation system according to claim 1 wherein the first, second, third and fourth reference frequency signals are 0°

, 180°

, 90° and

270°

phase shifted reference frequency signals, respectively.

4. A power modulation system according to claim 1 wherein the source of first, second, third and fourth reference frequency signals comprises:

a controlled oscillator that produces the first reference frequency signal;

a first inverter that is responsive to the controlled oscillator to produce the second reference frequency signal;

a phase shifter that is responsive to the controlled oscillator to produce the third reference frequency signal; and

a second inverter that is responsive to the phase shifter to produce the fourth reference frequency signal.

5. A power modulation system according to claim 1 wherein the switching system comprises:

a first switch that is responsive to the one of the I and Q input signals being positive to couple the first reference frequency signal to the first power amplifier, and that is responsive to the one of the I and Q input signals being negative to couple the second reference frequency signal to the first power amplifier; and

a second switch that is responsive to the other of the I and Q input signals being positive to couple the third reference frequency signal to the second power amplifier, and that is responsive to the other of the I and Q input signals being negative to couple the fourth reference frequency signal to the second power amplifier.

6. A power modulation system according to claim 5 wherein the switching system further comprises:

a first polarity detector that is coupled between the one of the I and Q input signals and the first switch, to detect whether the one of the I and Q input signals is positive or negative; and

a second polarity detector that is coupled between the other of the I and Q input signals and the second switch, to detect whether the other of the I and Q input signals is positive or negative.

7. A power modulation system according to claim 1 further comprising:

a first analog-to-digital converter that is coupled between the one of the I and Q input signals and the third amplifier, such that the third amplifier is responsive to a digital representation of the one of the I and Q signals to supply a first variable supply voltage to the supply input of the first amplifier; and

a second analog-to-digital converter that is coupled between the other of the I and Q input signals and the fourth amplifier, such that the fourth amplifier is responsive to a digital representation of the other of the I and Q signals to supply a second variable supply voltage to the supply input of the second amplifier.

8. A power modulation system according to claim 7 wherein the first analog-to-digital converter comprises a first delta-sigma analog-to-digital converter and wherein the second analog-to-digital converter comprises a second delta-sigma analog-to-digital converter.

9. A power modulation system according to claim 1 wherein the coupler comprises a matching network that couples the first and second power amplifiers to a load.

10. A power modulation system according to claim 9 wherein the coupler further comprises a first quarter wavelength transmission line that couples the first power amplifier to the matching network and a second quarter wavelength transmission line that couples the second power amplifier to the matching network.

11. A power modulation system according to claim 9 wherein the coupler further comprises a first isolator that couples, the first power amplifier to the matching network and a second isolator that couples the second power amplifier to the matching network.

12. A power modulation system according to claim 1 wherein the first and second power amplifiers produce nonlinear distortion, the power modulation system further comprising:

a compensation system that is responsive to the I and Q input signals, to generate predistorted I and Q signals and to apply the predistorted I and Q signals to at least one of the switching system and to the third and fourth amplifiers, to thereby compensate for the nonlinear distortion.

13. A power modulation system according to claim 12 wherein the compensation system comprises:

a look-up table that is responsive to the I input signal to produce a first amplitude distortion compensating value and a first phase compensating value, and that is responsive to the Q input signal to produce a second amplitude distortion compensating value and a second phase compensating value; and

a summer that adds the first amplitude distortion compensating value and the second phase compensating value to produce the predistorted I signal, and that subtracts the first phase compensating value from the second amplitude distortion compensating value to produce the predistorted Q signal.

14. A power modulation system according to claim 13:

wherein the look-up table is a pair of look-up subtables, a respective one of which is responsive to a respective one of the I input signal and the Q input signal; and

wherein the summer comprises an adder that adds the first amplitude distortion compensating value and the second phase compensating value to produce the predistorted I signal, and a subtractor that subtracts the first phase compensating value from the second amplitude distortion compensating value to produce the predistorted Q signal.

15. A power modulation system according to claim 1 wherein the I and Q input signals are I and Q radiotelephone communication signals and wherein the load is a radiotelephone antenna.

16. A power modulation system that modulates and amplifies in-phase (I) and quadrature-phase (Q) input signals, the power modulation system comprising:

first and second means for power amplifying a signal input to produce a power output in response to a supply input;

means for providing first, second, third and fourth reference frequency signals, the first and second reference frequency signals being inverted relative to one another and the third and fourth reference frequency signals being inverted relative to one another;

means for selectively applying one of the first and second reference frequency signals to the signal input of the first means for power amplifying as a function of the polarity of one of the I and Q input signals, and for selectively applying one of the third and fourth reference frequency signals to the signal input of the second means for power amplifying as a function of the polarity of the other of the I and Q input signals;

means for supplying a first variable supply voltage to the supply input of the first means for power amplifying in response to the one of the I and Q input signals;

means for supplying a second variable supply voltage to the supply input of the second means for power amplifying in response to the other of the I and Q input signals; and

means for coupling the power outputs of the first and second means for power amplifying to a load.

17. A power modulation system according to claim 16 wherein the first and second means for power amplifying comprise class-C power amplifiers and wherein the means for supplying comprise class-D power amplifiers.

18. A power modulation system according to claim 16 wherein the firsts second, third and fourth reference frequency signals are 0°

, 180°

, 90° and

270°

phase shifted reference frequency signals, respectively.

19. A power modulation system according to claim 16 wherein the means for providing first, second, third and fourth reference frequency signals comprises:

means for producing the first reference frequency signal;

means for inverting the first reference frequency signal to produce the second reference frequency signal;

means for phase shifting the first reference frequency signal to produce the third reference frequency signal; and

means for inverting the third reference frequency signal to produce the fourth reference frequency signal.

20. A power modulation system according to claim 16 wherein the means for selectively applying comprises:

first means for coupling the first reference frequency signal to the first power amplifying means in response to the one of the I and Q input signals being positive and for coupling the second reference frequency signal to the first power amplifying means in response to the one of the I and Q input signals being negative; and

second means for coupling the third reference frequency signal to the second power amplifying means in response to the other of the I and Q input signals being positive and for coupling the fourth reference frequency signal to the second power amplifying means in response to the other of the I and Q input signals being negative.

21. A power modulation system according to claim 20 wherein the means for selectively applying further comprises:

first means for detecting whether the one of the I and Q input signals is positive or negative, the first means for coupling being responsive to the first means for detecting; and

second means for detecting whether the other of the I and Q input signals is positive or negative, the second means for coupling being responsive to the second means for detecting.

22. A power modulation system according to claim 16 further comprising:

first means for converting the one of the I and Q input signals to digital, such that the means for supplying a first variable supply voltage is responsive to a digital representation of the one of the I and Q signals; and

second means for converting the other of the I and Q input signals to digital, such that the means for supplying a second variable supply voltage is responsive to a digital representation of the other of the I and Q signals.

23. A power modulation system according to claim 22 wherein the first means for converting comprises a first delta-sigma analog-to-digital converter and wherein the second means for converting comprises a second delta-sigma analog-to-digital converter.

24. A power modulation system according to claim 16 wherein the means for coupling comprises means for matching the first and second means for power amplifying to a load.

25. A power modulation system according to claim 24 wherein the means for coupling further comprises a first quarter wavelength transmission line that couples the first means for power amplifying to the means for matching and a second quarter wavelength transmission line that couples the second means for power amplifying to the means for matching.

26. A power modulation system according to claim 24 wherein the means for coupling further comprises means for isolating the first means for power amplifying and the second means for power amplifying from one another.

27. A power modulation system according to claim 24 wherein the means for matching comprises means for converting voltage to current.

28. A power modulation system according to claim 16 wherein the first and second means for power amplifying produce nonlinear distortion, the power modulation system further comprising:

means for generating predistorted I and Q signals from the I and Q input signals and for applying the predistorted I and Q signals to at least one of the means for selectively applying and the means for supplying, to thereby compensate for the nonlinear distortion.

29. A power modulation system according to claim 28 wherein the means for generating comprises:

means for producing a first amplitude distortion compensating value and a first phase compensating value in response to the I input signal and for producing a second amplitude distortion compensating value and a second phase compensating value in response to the Q input signal; and

means for adding the first amplitude distortion compensating value and the second phase compensating value to produce the predistorted I signal, and for subtracting the first phase compensating value from the second amplitude distortion compensating value to produce the predistorted Q signal.

30. A power modulation system according to claim 16 wherein the I and Q input signals are I and Q radiotelephone communication signals and wherein the load is a radiotelephone antenna.

31. A method for modulating and amplifying in-phase (I) and quadrature-phase (Q) input signals, using first and second means for power amplifying a signal input to produce a power output in response to a supply input, the method comprising the steps of:

providing first, second, third and fourth reference frequency signals, the first and second reference frequency signals being inverted relative to one another and the third and fourth reference frequency signals being inverted relative to one another;

selectively applying one of the first and second reference frequency signals to the signal input of the first means for power amplifying, as a function of the polarity of one of the I and Q input signals;

selectively applying one of the third and fourth reference frequency signals to the signal input of the second means for power amplifying as a function of the polarity of the other of the I and Q input signals;

supplying a first variable supply voltage to the supply input of the first means for power amplifying in response to the one of the I and Q input signals;

supplying a second variable supply voltage to the supply input of the second means for power amplifying in response to the other of the I and Q input signals; and

coupling the power outputs of the first and second means for power amplifying to a load.

32. A method according to claim 31 wherein the first and second means for power amplifying comprise class-C power amplifiers and wherein the supplying steps use class-D power amplifiers.

33. A method according to claim 31 wherein the first, second, third and fourth reference frequency signals are 0°

, 180°

, 90° and

270°

phase shifted reference frequency signals, respectively.

34. A method according to claim 31 wherein the step of providing first, second, third and fourth reference frequency signals comprises the steps of:

producing the first reference frequency signal;

inverting the first reference frequency signal to produce the second reference frequency signal;

phase shifting the first reference frequency signal to produce the third reference frequency signal; and

inverting the third reference frequency signal to produce the fourth reference frequency signal.

35. A method according to claim 31 wherein the steps of selectively applying comprise the steps of:

coupling the first reference frequency signal to the first power amplifying means in response to the one of the I and Q input signals being positive;

coupling the second reference frequency signal to the first power amplifying means in response to the one of the I and Q input signals being negative;

coupling the third reference frequency signal to the second power amplifying means in response to the other of the I and Q input signals being positive; and

coupling the fourth reference frequency signal to the second power amplifying means in response to the other of the I and Q input signals being negative.

36. A method according to claim 35 wherein the steps of selectively applying further comprise the steps of:

detecting whether the one of the I and Q input signals is positive or negative; and

detecting whether the other of the I and Q input signals is positive or negative.

37. A method according to claim 31 further comprising the steps of:

converting the one of the I and Q input signals to digital, such that the step of supplying a first variable supply voltage is responsive to a digital representation of the one of the I and Q signals; and

converting the other of the I and Q input signals to digital, such that the step of supplying a second variable supply voltage is responsive to a digital representation of the other of the I and Q signals.

38. A method according to claim 37 wherein the steps of converting comprise the steps of delta-sigma converting.

39. A method according to claim 31 wherein the step of coupling comprises the step of matching the first and second means for power amplifying to a load.

40. A method according to claim 39 wherein the step of coupling comprises the step of quarter wavelength transmission line matching the first means for power amplifying and the second means for power amplifying.

41. A method according to claim 39 wherein the step of coupling comprises the step of isolating the first means for power amplifying and the second means for power amplifying from one another.

42. A method according to claim 39 wherein the step of matching further comprises the step of converting voltage to current.

43. A method according to claim 31 wherein the first and second means for power amplifying produce nonlinear distortion, the power modulation method further comprising the step of:

generating predistorted I and Q signals from the I and Q input signals, at least one of the selectively applying steps and the supplying steps being responsive to the predistorted I and Q signals, to thereby compensate for the nonlinear distortion.

44. A method according to claim 43 wherein the generating step comprises the steps of:

producing a first amplitude distortion compensating value and a first phase compensating value in response to the I input signal;

producing a second amplitude distortion compensating value and a second phase compensating value in response to the Q input signal;

adding the first amplitude distortion compensating value and the second phase compensating value to produce the predistorted I signal; and

subtracting the first phase compensating value from the second amplitude distortion compensating value to produce the predistorted Q signal.

45. A power modulation method according to claim 31 wherein the I and Q input signals are I and Q radiotelephone communication signals and wherein the load is a radiotelephone antenna.

46. A system that amplifies in-phase (I) and quadrature-phase (Q) input signals, the system comprising:

first and second linear power amplifiers that also produce nonlinear distortion; and

a compensation system that is responsive to the I and Q input signals, to generate predistorted I and Q signals, to apply the predistorted I signal to the first linear power amplifier and to apply the predistorted Q signal to the second linear power amplifier, to thereby compensate for the nonlinear distortion that also is produced by the first and second linear power amplifiers.

47. A system according to claim 46 wherein the compensation system comprises:

a look-up table that is responsive to the I input signal to produce a first amplitude distortion compensating value and a first phase compensating value, and that is responsive to the Q input signal to produce a second amplitude distortion compensating value and a second phase compensating value; and

a summer that adds the first amplitude distortion compensating value and the second phase compensating value to produce the predistorted I signal, and that subtracts the first phase compensating value from the second amplitude distortion compensating value to produce the predistorted Q signal.

48. A system according to claim 47:

wherein the look-up table is a pair of look-up subtables, a respective one of which is responsive to a respective one of the I input signal and the Q input signal; and

wherein the summer comprises an adder that adds the first amplitude distortion compensating value and the second phase compensating value to produce the predistorted I signal, and a subtractor that subtracts the first phase compensating value from the second amplitude distortion compensating value to produce the predistorted Q signal.

49. A system that amplifies in-phase (I) and quadrature-phase (Q) input signals, the system comprising:

first and second means for linearly power amplifying that also produce nonlinear distortion; and

means for generating predistorted I and Q signals from the I and Q input signals, for applying the predistorted I signal to the first means for linearly power amplifying and for applying the predistorted Q signal to the second means for linearly power amplifying, to thereby compensate for the nonlinear distortion that also is produced by the first and second means for linearly power amplifying.

50. A power modulation system according to claim 49 wherein the means for generating comprises:

means for producing a first amplitude distortion compensating value and a first phase compensating value in response to the I input signal and for producing a second amplitude distortion compensating value and a second phase compensating value in response to the Q input signal; and

means for adding the first amplitude distortion compensating value and the second phase compensating value to produce the predistorted I signal, and for subtracting the first phase compensating value from the second amplitude distortion compensating value to produce the predistorted Q signal.

51. A method for amplifying in-phase (I) and quadrature-phase (Q) input signals, the method comprising the steps of:

generating predistorted I and Q signals from the I and Q input signals;

applying the predistorted I signal to a first linear power amplifier; and

applying the predistorted Q signal to a second linear power amplifier, to thereby compensate for nonlinear distortion that also is produced in the first and second linear power amplifier.

52. A method according to claim 51 wherein the generating step comprises the steps of:

producing a first amplitude distortion compensating value and a first phase compensating value in response to the I input signal;

producing a second amplitude distortion compensating value and a second phase compensating value in response to the Q input signal;

adding the first amplitude distortion compensating value and the second phase compensating value to produce the predistorted I signal; and

subtracting the first phase compensating value from the second amplitude distortion compensating value to produce the predistorted Q signal.