Power amplification for parametric loudspeaker

• US 20040047477A1
• Filed: 10/03/2003
• Published: 03/11/2004
• Est. Priority Date: 07/11/2001
• Status: Active Grant

• Current Assignee: Turtle Beach Corporation
• Original Assignee: American Technology Incorporated (Emerson Electric Company)
• Inventors: Bank, Jeevan, Croft lll, James
• Granted Patent: US 7,319,763 B2
• Time in Patent Office: Days
• US Class Current: 381/120
• CPC Class Codes: H03F 2200/541 Transformer coupled at the output of an amplifier
• CPC Class Codes: H03F 3/181 Low-frequency amplifiers, e.g. audio preamplifiers
• CPC Class Codes: H03F 3/2171 with field-effect devices H03F3/2173 - H03F3/2178 take precedence
• CPC Class Codes: H03F 3/2173 of the bridge type
• CPC Class Codes: H03F 3/2178 using more than one switch or switching amplifier in parallel or in series H03F3/2173, H03F3/2175 take precedence

Abstract

A power amplifier for a parametric loudspeaker system which utilizes switch-mode power conversion to increase efficiency. The power amplifier is configured to coordinate the switching frequency of the amplifier with the carrier frequency of the parametric loudspeaker system, so a lower switching frequency may be used even though the power amplifier must amplify ultrasonic signals. The amplifier can be further optimized to counteract the reactance of the transducer load at the carrier frequency.

Claims

1. A parametric loudspeaker system to provide improved power efficiency in a parametric power amplifier, comprising:

(a) a switching power stage in the power amplifier;

(b) a carrier frequency amplified by the switching power stage;

(c) an audio frequency range having corresponding sideband frequencies divergent from the carrier frequency, wherein the sideband frequencies are amplified by the switching power stage;

(d) at least one transducer, electrically coupled to the power amplifier; and

(e) at least one reactive circuitry element coupled between the switching power stage and the at least one transducer.

2. A parametric loudspeaker system as in claim 1, wherein the switching power stage utilizes pulse width modulation.

3. A parametric loudspeaker system as in claim 1, wherein the switching power stage operates as a Class D amplifier.

4. A parametric loudspeaker system as in claim 1, wherein the switching power stage has a switching frequency which corresponds to the carrier frequency of the parametric loudspeaker system.

5. A parametric loudspeaker system as in claim 4, wherein the switching frequency is substantially an integer multiple of a carrier frequency of the parametric loudspeaker system.

6. A parametric loudspeaker system as in claim 5, wherein the power amplifier operates in a three-state mode and the switching frequency of the switching power stage is substantially an even integer multiple of a carrier frequency of the parametric loudspeaker system.

7. A parametric loudspeaker system as in claim 6, wherein the switching frequency is a frequency of the parametric loudspeaker system selected from the group consisting of:

at least 2 times a carrier frequency, at least 4 times a carrier frequency, at least 6 times a carrier frequency.

8. A parametric loudspeaker system as in claim 6, wherein the switching frequency is a frequency at least 8 times a carrier frequency.

9. A parametric loudspeaker system as in claim 5, wherein the power amplifier operates in a two-state mode and the switching frequency of the switching power stage is substantially an odd integer multiple of a carrier frequency of the parametric loudspeaker system.

10. A parametric loudspeaker system as in claims 9, wherein the switching frequency is a frequency of the parametric loudspeaker system selected from the group consisting of:

at least 1 times a carrier frequency, at least 3 times a carrier frequency, at least 5 times a carrier frequency, and at least 7 times a carrier frequency.

11. A parametric loudspeaker system as in claim 9, wherein the switching frequency is a frequency at least 9 times a carrier frequency.

12. A parametric loudspeaker system as in claim 5 wherein the switching frequency of the switching power stage corresponds substantially to a multiple of a carrier frequency of the parametric loudspeaker system within a frequency tolerance limit corresponding to a lowest audible frequency limit of the parametric loudspeaker system.

13. A parametric loudspeaker system as in claim 12, wherein the lowest audible frequency limit of the parametric loudspeaker system is approximately 300 Hz and the frequency tolerance limit is less than 300 Hz.

14. A parametric loudspeaker system as in claim 12, wherein the frequency tolerance limit is less than the lowest audible frequency limit.

15. A parametric loudspeaker system as in claim 12, wherein the frequency tolerance limit is less than or equal to a multiple of the carrier times the lowest audible frequency limit.

16. A parametric loudspeaker system as in claim 12, wherein the frequency tolerance limit is determined by:

T_L<

(xC)*LFL

wherein

TL is the frequency tolerance limit;

(xC) is the multiple of the carrier being used;

LFL is the lowest frequency tolerance limit.

17. The parametric loudspeaker system as in claim 1, wherein one or more of the at least one reactive circuitry element is adapted to counteract a reactive load of the transducer at a frequency corresponding to the carrier frequency.

18. The parametric loudspeaker system as in claim 1, wherein the transducer further comprises a resonant frequency and the at least one reactive circuitry element is adapted to counteract a reactive load of the transducer at a frequency corresponding to the resonant frequency.

19. A parametric loudspeaker system as in claim 1, wherein the transducer further comprises a resonant frequency and the at least one reactive circuitry element is adapted to counteract a reactive load of the transducer at a frequency corresponding to an off-resonant frequency within an ultrasonic frequency range of the parametric loudspeaker system.

20. A parametric loudspeaker system to provide improved power efficiency in a parametric power amplifier, comprising:

(a) a switching power stage in the power amplifier;

(b) an ultrasonic carrier frequency amplified by the switching power stage;

(c) an audio frequency range having corresponding sideband frequencies divergent from the carrier frequency; and

(d) at least one transducer, electrically coupled to the power amplifier.

21. A parametric loudspeaker system as in claim 20, wherein the switching power stage has multiple power levels and uses switched amplitude power levels to provide power to a linear output stage.

22. A parametric loudspeaker system as in claim 21, wherein the switching power stage has at least two switched amplitude power levels.

23. A parametric loudspeaker system as in claim 20, further comprising an output coupling transformer including a lower level voltage tap and a higher level voltage tap at a first polarity and a lower level voltage tap and a higher level voltage tap at a second polarity that is opposite to the first polarity.

24. A parametric loudspeaker system as in claim 21, wherein the multiple power levels are provided by at least two positive transformer taps and at least two negative transformer taps.

25. A parametric loudspeaker system as in claim 21, wherein the multiple power levels include at least two positive and two negative power supply levels.

26. A parametric loudspeaker system to provide improved power efficiency in a parametric power amplifier, comprising:

(a) a switching power stage in the power amplifier;

(b) a carrier frequency amplified by the switching power stage;

(c) an audio frequency range having corresponding sideband frequencies divergent from the carrier frequency;

(d) at least one transducer, electrically coupled to the switching power stage, exhibiting a reactive load; and

(e) at least one reactive circuitry element, coupled between the switching power stage and the at least one transducer, configured to substantially counteract the reactive load of the transducer at a frequency corresponding to the carrier frequency.

27. The parametric loudspeaker system as in claim 26, wherein

the transducer exhibits a dominant capacitive reactance at a frequency which includes the carrier frequency;

and

the at least one reactive circuitry element further comprises an inductance.

28. The parametric loudspeaker system as in claim 26, wherein

the transducer exhibits a dominant inductive reactance at a frequency which includes the carrier frequency, and

the at least one reactive circuitry element further comprises a capacitance.

29. A parametric loudspeaker system to provide improved power efficiency when used in with a parametric power amplifier that amplifies a carrier frequency, comprising:

a transducer exhibiting a reactive load and at least one resonant frequency; and

reactive circuitry coupled between the power amplifier and the transducer to substantially counteract the reactive load of the transducer at a selected off-resonant frequency.

30. A parametric loudspeaker system as in claim 29, wherein

the transducer exhibits a dominant capacitive reactance at the off-resonant frequency;

and

the reactive circuitry further comprises at least one inductance.

31. A parametric loudspeaker system as in claim 30, wherein the reactive circuitry further comprises at least one capacitance.

32. A parametric loudspeaker system as in claim 29, wherein the reactive circuitry has a variable reactive value.

33. A parametric loudspeaker system as in claim 29, wherein the reactive circuitry is adapted to be varied in response to a change in a parameter of the transducer.

34. A parametric loudspeaker system as in claim 29, wherein the reactive circuitry is adapted to be varied in response to a change in the carrier frequency.

35. A parametric loudspeaker system as in claim 29, wherein the adjustable reactive circuitry is adapted to be varied in response to a change in the transducer resonant frequency.

36. A parametric loudspeaker system as in claim 29, wherein the reactive circuitry includes an inductance embodied in a saturable inductor.

37. A parametric loudspeaker system as in claim 29, wherein the carrier frequency is varied to accommodate changes in the at least one resonant frequency of the transducer related to changes in barometric pressure and altitude.

38. A parametric loudspeaker system to provide improved power efficiency when used with a parametric power amplifier that amplifies an ultrasonic carrier frequency, comprising:

a transducer exhibiting a reactive load; and

reactive circuitry, including at least one inductance and at least one capacitance, coupled between the power amplifier and the transducer to substantially counteract the reactive load of the transducer at a selected frequency.

39. A parametric loudspeaker system as in claim 38, wherein the at least one inductance is contained in the transducer.

40. A parametric loudspeaker system as in claim 39, wherein the selected frequency is the carrier frequency.

41. A parametric loudspeaker system as in claim 39, wherein the selected frequency is a resonant frequency of the transducer.

42. A parametric loudspeaker system as in claim 39, wherein the selected frequency is an off-resonant frequency of the transducer.

43. A parametric loudspeaker system as in claim 38, wherein the selected frequency is the carrier frequency.

44. A parametric loudspeaker system as in claim 38, wherein the selected frequency is a resonant frequency of the transducer.

45. A method for improving power efficiency in a parametric loudspeaker power amplifier, comprising the steps of:

(a) generating a pulse width modulation (PWM) signal;

(b) amplifying a parametric signal having a carrier frequency and audio related sideband signals using the PWM signal;

(c) delivering the parametric signal to at least one transducer having a reactive load; and

(d) counteracting the reactive load in the transducer using at least one reactive circuitry element.

46. A method as in claim 45, wherein step (a) further comprises the step of generating the pulse width modulation (PWM) signal at a switching frequency that is a multiple of the carrier frequency.

47. A method as in claim 45, wherein step (a) further comprises the step of generating the pulse width modulation (PWM) signal at a switching frequency that is an even multiple of the carrier frequency.

48. A method as in claim 45, wherein step (a) further comprises the step of generating the pulse width modulation (PWM) signal at a switching frequency that is an odd multiple of the carrier frequency.

53. A method as in claim 48, further comprising the step of providing multiple power levels using a switching power stage to provide power to a linear output stage.

54. A method as in claim 53, wherein the step of providing multiple power levels further comprises the step of using at least two positive transformer taps and at least two negative transformer taps to provide multiple power levels.

49. A method for eliminating the need for an isolation power transformer in an amplifier with a power output stage to amplify a signal delivered to a parametric loudspeaker, comprising the steps of:

(a) isolating small signal input circuitry from input power circuitry in the amplifier using input isolation componentry;

(b) isolating the amplifier output circuitry using an output isolation transformer; and

(c) delivering power from the input power circuitry to the amplifier output stage with direct off-line rectification without a power isolation transformer.

50. A method as in claim 49, wherein step (a) further comprises the step of isolating the input power circuitry using an opto-isolator.

51. A method as in claim 49, wherein step (a) further comprises the step of isolating the input power circuitry using an isolation transformer.

52. A method as in claim 49, further comprising the step of providing multiple power levels by including an output coupling transformer having a lower level voltage tap and a higher level voltage tap at a first polarity and a lower level voltage tap and a higher level voltage tap at a second polarity that is opposite to the first polarity.

55. A method for minimizing the reactance of a reactive load transducer at a selected frequency in an amplifier with a power output stage for amplifying a signal, comprising the steps of:

(a) supplying a signal to the power output stage of the amplifier which includes at least one reactive component coupled to the amplifier; and

(b) counteracting transducer reactance at the selected frequency by interacting the signal with the at least one reactive component.

56. A method as in claim 55, wherein step (b) further comprises counteracting the transducer reactance at the carrier frequency by interacting the signal with the at least one reactive component.

57. A method as in claim 55, wherein step (b) further comprises counteracting the transducer reactance at a transducer=s resonant frequency by interacting the signal with the at least one reactive component.

58. A method as in claim 55, wherein step (b) further comprises counteracting the transducer reactance at a transducer'"'"'s off-resonant frequency by interacting the signal with the at least one reactive components.

59. A method as in claim 55, wherein step (b) further comprises counteracting the transducer reactance of a capacitive transducer load using at least one inductively reactive component.

60. A method as in claim 55, wherein step (b) further comprises counteracting the transducer reactance of an inductive transducer load using at least one capacitively reactive component.

61. A method for using a switch-mode power amplifier at high efficiency with a carrier frequency based parametric loudspeaker, comprising the steps of:

(a) establishing a parametric loudspeaker carrier frequency;

(b) producing a switching frequency through the switch-mode power amplifier, that is an integer multiple of the carrier frequency of the parametric loudspeaker.

62. A method as in claim 61, wherein step (b) further comprises producing a switching frequency through the switch-mode power amplifier that is an even integer multiple of a carrier frequency of the parametric loudspeaker.

63. A method as in claim 61, further comprising the step of producing the switching frequency at a frequency at least 1 times a carrier frequency of the parametric loudspeaker.

64. A method as in claim 61, further comprising the step of producing the switching frequency at a frequency at least 2 times a carrier frequency of the parametric loudspeaker.

65. A method as in claim 61, further comprising the step of producing the switching frequency at a frequency at least 4 times a carrier frequency of the parametric loudspeaker.

66. A method as in claim 61, further comprising the step of producing the switching frequency at a frequency at least 6 times a carrier frequency of the parametric loudspeaker.

67. A method as in claim 61, further comprising the step of producing the switching frequency at a frequency at least 8 times a carrier frequency of the parametric loudspeaker.

68. A method as in claim 61, wherein step (b) further comprises producing a switching frequency through the switch-mode power amplifier that is an odd multiple of a carrier frequency of the parametric loudspeaker.