Microwave doherty amplifier

• US 5,420,541 A
• Filed: 06/04/1993
• Issued: 05/30/1995
• Est. Priority Date: 06/04/1993
• Status: Expired due to Term

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: McMorrow, Robert J., Upton, David M.
• Primary Examiner(s): Mottola, Steven
• Assistant Examiner(s): NGUYEN, TIEP HUU
• Application Number:
  US08/072,267
• Time in Patent Office: 725 Days
• Field of Search: 330/295, 330/286, 330/53, 330/54, 330/124 R
• US Class Current: 330/286
• CPC Class Codes: H03F 1/0288 using a main and one or several auxiliary peaking amplifiers whereby the load is connected to the main amplifier using an impedance inverter, e.g. Doherty amplifiers
• CPC Class Codes: H03F 3/602 Combinations of several amplifiers

Abstract

An improved Doherty amplifier for operation at microwave frequencies using microstrip circuit technology and gallium arsenide devices to achieve greater efficiency and linearity. The circuit divides the input power equally between a carrier amplifier and peak amplifier with a quarter-wave delay at the input to the peak amplifier insuring that the output power of the two amplifiers will be in phase at the load. A three-port network combines the phase-delayed carrier amplifier output with the output of the peak amplifier. The outputs of the two amplifiers are connected together by a quarter wave transmission line of impedance R. A load of one-half the optimum load (R/2) is attached to the output of the peak amplifier. A quarter-wave line section provides the transition from R/2 to the desired impedance, R. When the peak amplifier is off, its output impedance is infinite and the output power of the carrier amplifier is delivered entirely to the load. As the peak amplifier becomes more active, it delivers more of its output power to the load while its output current gradually reduces the effective load impedance seen by the carrier amplifier thus allowing it to deliver more power. In this way the microwave Doherty amplifier allows 6 dB of linear power amplification beyond the point where a normal Class "B" amplifier begins to saturate and the microwave amplifier efficiency remains close to the maximum attainable linear efficiency.

Claims

1. A microwave frequency amplifier comprising:

phase quadrature producing means coupled to an input signal for producing a phase quadrature relationship over a broad-band between a first output signal and a second output signal from said phase quadrature producing means;

carrier amplifier means for amplifying said first output signal from said phase quadrature producing means;

peak amplifier means for amplifying said second output signal from said phase quadrature producing means;

distributed line means coupled between an output of said carrier amplifier means and an output of said peak amplifier means for controlling a phase of said output of said carrier amplifier means relative to the output of said peak amplifier means whereby said carrier amplifier means output and said peak amplifier means output combine in additive phase, and said distributed line means further provides impedance transforming action to an apparent load presented to said carrier amplifier means as a function of a degree of conduction of said peak amplifying means;

predetermined output impedance producing means coupled to said distributed line means and said output of said peak amplifier means for producing a predetermined output impedance of said microwave frequency amplifier;

said predetermined output impedance producing means comprises means for providing an operational voltage source for said carrier amplifier means and said peak amplifier means; and

said microwave frequency amplifier operates over a plurality of microwave frequencies including 1300 MHz.

2. The microwave frequency amplifier as recited in claim 1 wherein:

said input signal comprises multi-carrier signals.

3. The microwave frequency amplifier as recited in claim 1 wherein:

said input signal comprises a continuous single carrier that varies in amplitude.

4. The microwave frequency amplifier as recited in claim 1 wherein:

said input signal comprises a multi-carrier signal with each carrier signal varying in amplitude.

5. The microwave frequency amplifier as recited in claim 1 wherein:

said carrier amplifier means comprises a gallium arsenide semiconductor device.

6. The microwave frequency amplifier as recited in claim 1 wherein:

said peak amplifier means comprises a gallium arsenide semiconductor device.

7. The microwave frequency amplifier as recited in claim 1 wherein:

said distributed line means comprises a quarter-wave transformer.

8. The microwave frequency amplifier as recited in claim 1 wherein:

said degree of conduction of said peak amplifier means is determined by an input drive level of said second output signal from said phase quadrature producing means relative to a predetermined control input applied to said peak amplifier means.

9. A microwave frequency amplifier comprising:

phase quadrature producing means coupled to an input signal for producing a phase quadrature relationship over a broad-band between a first output signal and a second output signal from said phase quadrature producing means;

means for amplifying said first output signal;

first matching means coupled between said first output signal and said first output signal amplifying means for matching an impedance at an input of said first output signal amplifying means to an output impedance of said first output signal, said first matching means providing a low DC resistance and low reactance path at a frequency of a modulation envelope at baseband and providing sufficient RF signal isolation at a carrier frequency in order to bias said first output signal amplifying means;

means for amplifying said second output signal;

second matching means coupled between said second output signal and said second output signal amplifying means for matching an impedance at an input of said second output signal amplifying means to an output impedance of said second output signal, said second matching means providing a low DC resistance and low reactance path at the frequence of the modulation envelope at baseband and providing sufficient RF signal isolation at the carrier frequency in order to bias said second output signal amplifying means;

a first biasing means coupled to said first matching means for providing a bias to a control input of said first output signal amplifying means;

a second biasing means coupled to said second matching means for providing a bias to a control input of said second output signal amplifying means;

distributed line means coupled between an output of said first output signal amplifying means and an output of said second output signal amplifying means for controlling a phase of said output of said first output signal amplifying means relative to said output of said second output signal amplifying means whereby said first output signal amplifying means output and said second output signal amplifying means output combine in additive phase, and said distributed line means further provides impedance transforming action to an apparent load presented to said first output signal amplifying means as a function of a degree of conduction of said second output signal amplifying means;

predetermined output impedence producing means coupled to said distributed line means and said output of said second output signal amplifying means for producing a predetermined output impedance of said microwave frequency amplifier; and

said predetermined output impedance producing means comprises means for providing an operational voltage source for said first output signal amplifying means and said second output signal amplifying means.

10. The microwave frequency amplifier as recited in claim 9 wherein:

said microwave frequency amplifier operates over a plurality of microwave frequencies including 1300 MHz.

11. The microwave frequency amplifier as recited in claim 10 wherein:

said degree of conduction of said second output signal amplifying means is determined by an input drive level relative to a predetermined control input applied to said second output signal amplifying means.

12. The microwave frequency amplifier as recited in claim 10 wherein said first matching means and said second matching means each comprises a band-pass network.

13. The microwave frequency amplifier as recited in claim 10 wherein each of said first and second biasing means comprises a bias voltage.

14. The microwave frequency amplifier as recited in claim 10 wherein:

a voltage source for a first output signal amplifying means is coupled to said first reactive network means.

15. The microwave frequency amplifier as recited in claim 10 wherein:

a voltage source for a second output signal amplifying means is coupled to said second reactive network means.

16. The microwave frequency amplifier as recited in claim 9 wherein:

said input signal comprises multi-carrier signals.

17. The microwave frequency amplifier as recited in claim 9 wherein:

said input signal comprises a continuous single carrier that varies in amplitude.

18. The microwave frequency amplifier as recited in claim 9 wherein:

said input signal comprises a multi-carrier signal with each carrier signal varying in amplitude.

19. The microwave frequency amplifier as recited in claim 9 wherein:

said first output signal amplifying means comprises a gallium arsenide semiconductor device.

20. The microwave frequency amplifier as recited in claim 9 wherein:

said second output signal amplifying means comprises a gallium arsenide semiconductor device.

21. The microwave frequency amplifier as recited in claim 9 wherein:

said distributed line means comprises a quarter-wave transformer.

22. The microwave frequency amplifier as recited in claim 9 wherein:

said predetermined output impedance producing means comprises a transmission line connected to the distributed line means.

23. The microwave frequency amplifier as recited in claim 9 wherein:

said degree of conduction of said second output signal amplifying means is determined by an input drive level relative to said control input applied to said second output signal amplifying means.

24. The microwave frequency amplifier as recited in claim 9 wherein said first matching means and said second matching means each comprises a transmission line.

25. The microwave frequency amplifier as recited in claim 9 wherein each of said first and second bias means comprises a bias tee.

26. The microwave frequency amplifier as recited in claim 9 wherein:

said second output signal amplifying means comprises a gallium arsenide semiconductor device.

27. A microwave frequency amplifier comprising:

phase quadrature producing means coupled to an input signal for producing a phase quadrature relationship over a broad-band between a first output signal and a second output signal from said phase quadrature producing means;

means for amplifying said first output signal;

first matching means coupled between said first output signal and said first output signal amplifying means for matching an impedance at an input of said first output signal amplifying means to an output impedance of said first output signal;

means for amplifying said second output signal;

second matching means coupled between said second output signal and said second output signal amplifying means for matching an impedance at an input of said second output signal amplifying means to an output impedance of said second output signal;

means coupled to said first matching means for providing a bias to a control input of said first output signal amplifying means;

means coupled to said second matching means for providing a bias to a control input of said second output signal amplifying means;

distributed line means coupled between an output of said first output signal amplifying means and an output of said second output signal amplifying means for controlling a phase of said output of said first output signal amplifying means relative to the output of said second output signal amplifying means whereby said first output signal amplifying means output and said second output signal amplifying means output combine in additive phase and said distributed line means further provides impedance transforming action to an apparent load presented to said first output signal amplifying means as a function of a degree of conduction of said second output signal amplifying means;

means coupled to said distributed line means and said output of said second output signal amplifying means for providing an output matching network;

first reactive network means coupled to said first output signal amplifying means output for canceling capacitance present at said first output signal amplifying means output; and

second reactive network means coupled to said second output signal amplifying means for canceling capacitance present at said second output signal amplifying means output.

28. The microwave frequency amplifier as recited in claim 27 wherein:

said microwave frequency amplifier operates over a plurality of microwave frequencies including 1300 MHz.

29. The microwave frequency amplifier as recited in claim 27 wherein:

said input signal comprises multi-carrier signals.

30. The microwave frequency amplifier as recited in claim 27 wherein:

said input signal comprises a continuous single carrier that varies in amplitude.

31. The microwave frequency amplifier as recited in claim 27 wherein:

said input signal comprises a multi-carrier signal with each carrier signal varying in amplitude.

32. The microwave frequency amplifier as recited in claim 27 wherein:

said first output signal amplifying means comprises a first gallium arsenide semiconductor device.

33. A microwave frequency amplifier comprising:

phase quadrature producing means coupled to an input signal for producing a phase quadrature relationship over a broad-band between a first output signal and a second output signal from said phase quadrature producing means;

means for amplifying said first output signal;

first matching means coupled between said first output signal and said first output signal amplifying means for matching an impedance at an input of said first output signal amplifying means to an output impedance of said first output signal;

means for amplifying said second output signal;

second matching means coupled between said second output signal and said second output signal amplifying means for matching an impedance at an input of said second output signal amplifying means to an output impedance of said second output signal;

means coupled to said first matching means for providing a bias to a control input of said first output signal amplifying means;

means coupled to said second matching means for providing a bias to a control input of said second output signal amplifying means;

distributed line means coupled between an output of said first output signal amplifying means and an output of said second output signal amplifying means for controlling a phase of said output of said first output signal amplifying means relative to an output of said second output signal amplifying means whereby said first output signal amplifying means output and said second output signal amplifying means output combine in additive phase and said distributed line means further provides impedance transforming action to an apparent load presented to said first output signal amplifying means as a function of a degree of conduction of said second output signal amplifying means;

means coupled to said distributed line means and said output of said second output signal amplifying means for providing an output matching network;

first reactive network means coupled to said first output signal amplifying means output for canceling capacitance present at said first output signal amplifying means output;

second reactive network means coupled to said second output signal amplifying means for canceling capacitance present at said second output signal amplifying means output;

means coupled to said first output signal amplifying means output for providing zero impedance to a second harmonic of a design frequency at said first output signal amplifying means output; and

means coupled to said second output signal amplifying means output for providing zero impedance to a second harmonic of a design frequency at said second output signal amplifying means output.

34. The microwave frequency amplifier as recited in claim 33 wherein:

said microwave frequency amplifier operates over a plurality of microwave frequencies including 1300 MHz.

35. The microwave frequency amplifier as recited in claim 33 wherein:

said input signal comprises multi-carrier signals.

36. The microwave frequency amplifier as recited in claim 33 wherein:

said input signal comprises a continuous single carrier that varies in amplitude.

37. The microwave frequency amplifier as recited in claim 33 wherein:

said input signal comprises a multi-carrier signal with each carrier signal varying in amplitude.

38. The microwave frequency amplifier as recited in claim 33 wherein:

said first output signal amplifying means comprises a gallium arsenide semiconductor device.

39. The microwave frequency amplifier as recited in claim 33 wherein:

said second output signal amplifying means comprises a gallium arsenide semiconductor device.

40. The microwave frequency amplifier as recited in claim 33 wherein:

said degree of conduction of said second output signal amplifying means is determined by an input drive level relative to said control input applied to said second output signal amplifying means.

41. The microwave frequency amplifier as recited in claim 33 wherein said first matching means and said second matching means each comprises a band-pass network.

42. The microwave frequency amplifier as recited in claim 33 wherein said biasing means comprises a bias voltage.

43. The microwave frequency amplifier as recited in claim 33 wherein:

a voltage source for said first output signal amplifying means is coupled to said first reactive network means.

44. The microwave frequency amplifier as recited in claim 33 wherein:

a voltage source for said second output signal amplifying means is coupled to said second reactive network means.

45. A method of operating a high efficiency microwave frequency amplifier comprising the steps of:

providing a phase quadrature relationship over a broad-band between a first output signal and a second output signal from a phase quadrature producing means coupled to an input signal;

amplifying said first output signal from said phase quadrature producing means with a carrier amplifier means;

amplifying said second output signal from said phase quadrature producing means with a peak amplifier means;

controlling a phase of said output of said carrier amplifier means relative to the output of said peak amplifier means with a distributed line means coupled between an output of said carrier amplifier and an output of said peak amplifier whereby said carrier amplifier means output and said peak amplifier means output combine in additive phase, and said distributed line means further providing impedance transforming action to an apparent load presented to said carrier amplifier means as a function of a degree of conduction of said peak amplifier means;

producing a predetermined output impedance of said microwave frequency amplifier with means coupled to said distributed line means and said output of said peak amplifier means;

providing an operational voltage source for said carrier amplifier means and said peak amplifier means from said predetermined output impedance producing means; and

operating said microwave frequency amplifier over a plurality of microwave frequencies including 1300 MHz.

46. The method as recited in claim 45 wherein said step of providing a phase quadrature relationship comprises the step of said phase quadrature producing means being coupled to an input signal having multi-carrier signals.

47. The method as recited in claim 45 wherein said step of providing a phase quadrature relationship comprises the step of said phase quadrature producing means being coupled to an input signal having a continuous single carrier that varies in amplitude.

48. The method as recited in claim 45 wherein said step of providing a phase quadrature relationship comprises the step of said phase quadrature producing means being coupled to an input signal having a multi-carrier signal with each carrier signal varying in amplitude.

49. The method as recited in claim 45 wherein said step of amplifying said first output signal includes the step of operating a gallium arsenide semiconductor device.

50. The method as recited in claim 45 wherein said step of amplifying said second output signal includes the step of operating a gallium arsenide semiconductor device.

51. A method of operating a microwave frequency amplifier having improved efficiency and linearity comprising the steps of:

producing a phase quadrature relationship over a broad-band between a first output signal and a second output signal from a phase quadrature producing means coupled to an input signal;

amplifying said first output signal;

matching an impedance at an input of said first output signal amplifying means to an output impedance of said first output signal with a first matching means coupled between said first output signal and said first output signal amplifying means, said first matching means providing a low DC resistance and low reactance path at a frequency of a modulation envelope at baseband and providing sufficient RF signal isolation at a carrier frequency in order to bias said first output signal amplifying means;

amplifying said second output signal;

matching an impedance at an input of said second output signal amplifying means to an output impedance of said second output signal with a second matching means coupled between said second output signal and said second output signal amplifying means, said second matching means providing a low DC resistance and low reactance path at a frequency of a modulation envelope at baseband and providing sufficient RF signal isolation at a carrier frequency in order to bias said second output signal amplifying means;

biasing a control input of said first output signal amplifying means with a first biasing means coupled to said first matching means;

biasing a control input of said second output signal amplifying means with a second biasing means coupled to said second matching means;

controlling a phase of said output of said first output signal amplifying means relative to the output of said second output signal amplifying means with a distributed line means coupled between an output of said first output signal amplifying means and an output of said second output signal amplifying means, whereby said first output signal amplifying means output and said second output signal amplifying means output combine in additive phase, and said distributed line means further providing impedance transforming action to an apparent load presented to said first output signal amplifying means as a function of a degree of conduction of said second output signal amplifying means;

producing a predetermined output impedance of said microwave frequency amplifier with means coupled to said distributed line means and said output of said second output signal amplifying means; and

providing an operational voltage source for said first output signal amplifying means and said second output signal amplifying means from said predetermined output impedance producing means.

52. The method as recited in claim 51 wherein said microwave frequency amplifier operates over a plurality of microwave frequencies including 1300 MHz.

53. The method as recited in claim 51 wherein said step of providing a phase quadrature relationship comprises the step of said phase quadrature producing means being coupled to an input signal having multi-carrier signals.

54. The method as recited in claim 51 wherein said step of providing a phase quadrature relationship comprises the step of said phase quadrature producing means being coupled to an input signal having a continuous single carrier that varies in amplitude.

55. The method as recited in claim 51 wherein said step of providing a phase quadrature relationship comprises the step of said phase quadrature producing means being coupled to an input signal having multi-carrier signals with each carrier signal varying in amplitude.

56. The method as recited in claim 51 wherein said step of amplifying said first output signal includes the step of operating a gallium arsenide semiconductor device.

57. The method as recited in claim 51 wherein said step of amplifying said second output signal includes the step of operating a gallium arsenide semiconductor device.

58. A method of operating a microwave frequency amplifier having improved efficiency and linearity comprising the steps of:

producing a phase quadrature relationship over a broad-band between a first output signal and a second output signal from a phase quadrature producing means coupled to an input signal;

amplifying said first output signal;

matching an impedance at an input of said first output signal amplifying means to an output impedance of said first output signal with a first matching means coupled between said first output signal and said first output signal amplifying means;

amplifying said second output signal;

matching an impedance at an input of said second output signal amplifying means to an output impedance of said second output signal with a second matching means coupled between said second output signal and said second output signal amplifying means;

biasing a control input of said first output signal amplifying means with a first biasing means coupled to said first matching means;

biasing a control input of said second output signal amplifying means with a second biasing means coupled to said second matching means;

controlling a phase of said output of said first output signal amplifying means relative to an output of said second output signal amplifying means with a distributed line means coupled between an output of said first output signal amplifying means and an output of said second output signal amplifying means, whereby said first output signal amplifying means output and said second output signal amplifying means output combine in additive phase, and said distributed line means further providing impedance transforming action to an apparent load presented to said first output signal amplifying means as a function of a degree of conduction of said second output signal amplifying means;

producing a predetermined output impedance of said microwave frequency amplifier with means coupled to said distributed line means and said output of said second output signal amplifying means;

canceling capacitance present at said first output signal amplifying means output with a first reactive network means coupled to said first output signal amplifying means output;

canceling capacitance present at said second output signal amplifying means output with a second reactive network means coupled to said second output signal amplifying means;

providing zero impedance to a second harmonic of a design frequency at said first output signal amplifying means output with means coupled to said first output signal amplifying means output; and

providing zero impedance to a second harmonic of a design frequency at said second output signal amplifying means output with means coupled to said second output signal amplifying means output.

60. The method as recited in claim 58 wherein said step of providing a phase quadrature relationship comprises the step of said phase quadrature producing means being coupled to an input signal having multi-carrier signals.

61. The method as recited in claim 58 wherein said step of providing a phase quadrature relationship comprises the step of said phase quadrature producing means being coupled to an input signal having a continuous single carrier that varies in amplitude.

62. The method as recited in claim 58 wherein said step of providing a phase quadrature relationship comprises the step of said phase quadrature producing means being coupled to an input signal having a multi-carrier signal with each carrier signal varying in amplitude.

63. The method as recited in claim 58 wherein said step of amplifying said first output signal includes the step of operating a gallium arsenide semiconductor device.

64. The method as recited in claim 58 wherein said step of amplifying said second output signal includes the step of operating a gallium arsenide semiconductor device.

59. The method as recited in claim 59 wherein said microwave frequency amplifier operates over a plurality of microwave frequencies including 1300 MHz.