Power amplification using a direct-upconverting quadrature mixer topology

• US 6,307,894 B2
• Filed: 05/25/1999
• Issued: 10/23/2001
• Est. Priority Date: 05/25/1999
• Status: Expired due to Term

• Current Assignee: Skyworks Solutions Incorporated
• Original Assignee: Conexant Systems Incorporated (Synaptics Incorporated)
• Inventors: Eidson, Donald Brian, Grange, Robert Edmund
• Primary Examiner(s): Pham, Chi
• Assistant Examiner(s): PHU, PHUONG M
• Application Number:
  US09/318,482
• Publication Number:
  US 20010016016A1
• Time in Patent Office: 882 Days
• Field of Search: 375/297, 375/295, 375/302, 375/298, 455/118, 455/333, 455/127, 455/103, 455/110, 455/112, 327/355, 327/357, 327/359, 327/556, 327/113, 327/116
• US Class Current: 375/297
• CPC Class Codes: H03C 3/40 using two signal paths the outputs of which have a predetermined phase difference and at least one output being amplitude-modulated
• CPC Class Codes: H03D 2200/0007 Dual gate field effect transistors
• CPC Class Codes: H03D 7/1433 using bipolar transistors H03D7/145 takes precedence
• CPC Class Codes: H03D 7/1441 using field-effect transistors H03D7/145 takes precedence
• CPC Class Codes: H03D 7/1458 Double balanced arrangements, i.e. where both input signals are differential
• CPC Class Codes: H03D 7/165 at least two frequency changers being located in different paths, e.g. in two paths with carriers in quadrature combined with amplitude demodulation H03D1/2245, combined with angle demodulation H03D3/007; N-path filters H03H19/002
• CPC Class Codes: H03F 3/211 using a combination of several amplifiers H03F3/60 takes precedence
• CPC Class Codes: H04L 27/2071 in which the data are represented by the carrier phase, e.g. systems with differential coding

Abstract

A power amplifier for use in a wireless communication system operates like a quadrature mixer with conversion gain. The amplifier includes a local oscillator that generates two reference signals 90° out of phase with respect to each other. Four quadrature mixer elements receive signals representing the in-phase and quadrature components of a baseband signal. Each quadrature mixer amplifies the in-phase or the quadrature component of the baseband signal while upconverting with the corresponding reference signal.

Claims

1. A power amplifier comprising:

(a) an oscillator circuit configured to generate reference signals that are 90°

out of phase with respect to each other; and

(b) a quadrature mixer having;

(1) a plurality of mixer elements forming a final gain stage of the power amplifier, each connected by predetermined low impedance inputs with the oscillator circuit to receive one of the reference signals at an RF frequency, and each configured to;

(A) receive a signal at a baseband centered frequency through relatively high impedance inputs, the signal containing either an in-phase (I) component or a quadrature (Q) component of a baseband signal to be transmitted; and

(B) use one of the reference signals to simultaneously upconvert and amplify the in-phase or the quadrature component of the baseband signal; and

(2) combining circuitry configured to combine the upconverted and amplified I and Q components received from the mixer elements to form an output signal.

2. The power amplifier of claim 1, wherein the reference signals have power levels much greater than the power levels of the I and Q components of the baseband signal.

3. The power amplifier of claim 1, wherein at least one of the mixer elements includes a power transistor that receives one of the reference signals as input.

4. The power amplifier of claim 1, wherein the quadrature mixer includes a Gilbert cell optimized for power-handling capabilities.

5. The power amplifier of claim 3, wherein the power transistor includes a dual-gate FET.

6. The power amplifier of claim 3, wherein at least one of the mixer elements has a modulating port driven by the reference signal and a reference port driven by the in-phase or quadrature component of the baseband signal.

7. The power amplifier of claim 6, wherein the reference port is biased to act as an ON/OFF switch.

8. The power amplifier of claim 1, wherein the predetermined low impedance inputs are 50 ohms of impedance and the relatively high impedance inputs are much greater than the predetermined low impedance inputs.

9. The power amplifier of claim 7, wherein the modulating port is biased to act as a current source.

10. The power amplifier of claim 1, wherein each of the mixer elements is configured to operate as a controlled current source coupled to an ON/OFF switch.

11. The power amplifier of claim 10, wherein the ON/OFF switch is a power device.

12. The power amplifier of claim 1, comprising four mixer elements, each of which is configured to receive one of a group of signals representing the in-phase, negative in-phase, quadrature, and negative quadrature components of the baseband signal.

13. The power amplifier of claim 12, wherein the oscillator circuit is configured to produce four reference signals, three of which are 90°

, 180°

, and 270°

out of phase with respect to the other.

14. The power amplifier of claim 13, wherein the oscillator circuit includes a four-phase, ¼

-wavelength branch tap to generate the four reference signals.

39. The power amplifier of claim 1, wherein the combining circuitry is tuned to increase output power conversion efficiency of the quadrature mixer and reduce the appearance of amplifier output harmonics from the quadrature mixer.

15. A wireless transmitter for transmitting an amplified RF signal comprising:

(a) a baseband encoder that receives digital information and produces signals at a baseband centered frequency representing an in-phase (I) component and a quadrature (Q) component of a baseband signal to be transmitted;

(b) an oscillator circuit configured to generate reference signals at an RF frequency that are 90°

out of phase with respect to each other; and

(c) a quadrature mixer having;

(1) a plurality of mixer elements forming a final gain stage of the wireless transmitter, each connected to the oscillator circuit to receive one of the reference signals with inputs of predetermined low impedance and connected to the baseband encoder to receive one of the components of the baseband signal with inputs of relatively high impedance, each mixer element configured to operate as both a mixer and an amplifier using at least one of the reference signals to simultaneously modulate and impart conversion gain to the in-phase or the quadrature component of the baseband signal; and

(2) combining circuitry tuned to maximize the overall power conversion efficiency of the quadrature mixer, the combining circuitry configured to combine the modulated and amplified I and Q components to form the amplified RF signal.

16. The wireless transmitter of claim 15, wherein the reference signals have power levels much greater than the power levels of the I and Q components of the baseband signal.

17. The wireless transmitter of claim 15, wherein at least one of the mixer elements includes a power transistor that receives one of the reference signals as input.

18. The power amplifier of claim 15, wherein the quadrature mixer includes a Gilbert cell optimized for power-handling capabilities.

19. The wireless transmitter of claim 17, wherein the power transistor includes a dual-gate FET.

20. The wireless transmitter of claim 17, wherein at least one of the mixer elements has a modulating port driven by the reference signal and a reference port driven by the in-phase or quadrature component of the baseband signal.

21. The wireless transmitter of claim 20, wherein the reference port is biased to act as an ON/OFF switch.

22. The wireless transmitter of claim 21, wherein the modulating port is biased to act as a current source.

23. The wireless transmitter of claim 15, further comprising an element configured to produce four baseband signals representing the in-phase and inverted in-phase components and the quadrature and inverted quadrature components of the baseband signal.

24. The wireless transmitter of claim 23, comprising four mixer elements, each of which is configured to receive one of the four baseband signals.

25. The wireless transmitter of claim 23, wherein the oscillator circuit is configured to produce four reference signals, three of which are 90°

, 180°

, and 270°

out of phase with respect to the other.

26. The wireless transmitter of claim 25, wherein the oscillator circuit includes a four-phase, ¼

-wavelength branch tap to generate the four reference signals.

27. The wireless transmitter of claim 15, further comprising a low-loss combiner coupled to the quadrature mixer elements.

28. The wireless transmitter of claim 27, wherein the low-loss combiner includes a ceramic substrate.

29. A method for amplifying a baseband signal to be transmitted over a wireless network, the method comprising:

(a) providing amplified reference signals at an RF frequency that are 90°

out of phase with respect to each other to inputs of a quadrature mixer with predetermined low impedance;

(b) providing an in-phase (I) and quadrature (Q) component of the baseband signal at a baseband centered frequency to inputs of the quadrature mixer with relatively high impedance;

(c) operating the quadrature mixer as a both a final gain stage and a mixer such that at least one of the reference signals upconverts and at the same time amplifies the in-phase and the quadrature components of the baseband signal; and

(d) combining the upconverted and amplified I and Q components to form an output signal.

30. The method of claim 29, comprising providing at least one of the reference signals to a power transistor in the quadrature mixer.

31. The method of claim 30, wherein providing at least one of the reference signals to a power transistor includes providing the reference signal to a dual-gate FET.

32. The method of claim 30, further comprising driving a modulating port of the quadrature mixer with one of the reference signals and driving a reference port with either the in-phase or the quadrature component of the baseband signal.

33. The method of claim 32, further comprising biasing the reference port to act as an ON/OFF switch.

34. The method of claim 32, further comprising biasing the modulating port to act as a variable current source.

35. The method of claim 29, wherein the quadrature mixer includes four mixer elements.

36. The method of claim 35, comprising providing one of a group of signals to each of the mixer elements, where the group includes signals representing the in-phase and inverted in-phase components and the quadrature and inverted quadrature components of the baseband signal.

37. The method of claim 36, comprising providing one of four reference signals to each of the mixer elements, where three of the reference signals are 90°

, 180°

, and 270°

out of phase with respect to another of the reference signals.

38. The method of claim 37, further comprising using a four-phase, ¼

-wavelength branch tap to generate the reference signals.

40. The method of claim 29 further comprising the initial step of tuning combining circuitry within the quadrature mixer to increase output power conversion efficiency of the quadrature mixer and reduce the appearance of amplifier output harmonics from the quadrature mixer during the performance of (d).

41. A power mixer for generating an amplified signal from an in-phase (I) component and a quadrature (Q) component of a baseband signal, the power mixer comprising:

an oscillator circuit configured to generate a reference signal; and

a quadrature mixer electrically connected with the oscillator circuit, comprising;

a dual port transistor that receives the reference signal at an RF frequency with a predetermined low impedance input and the baseband signal at a baseband centered frequency with a relatively high impedance input, wherein the dual port transistor is operable as both a mixing stage and a final stage conversion gain to modulate and amplify versions of the in-phase (I) component and the quadrature (Q) component.

42. The power mixer of claim 41, further comprising a signal combiner electrically connected with the dual port transistor, the signal combiner being operable to combine the modulated and amplified versions of the in-phase (I) component and the quadrature (Q) component to form the amplified signal.

43. The power amplifier of claim 42, wherein the signal combiner is tuned to increase output power conversion efficiency of the quadrature mixer and reduce the appearance of amplifier output harmonics from the quadrature mixer.

44. The power mixer of claim 41, wherein the dual port transistors form a plurality of mixers.

45. The power mixer of claim 41, wherein the dual port transistors are field effect transistors.

46. The power mixer of claim 41, wherein the dual port transistors are bipolar transistors.

47. The power mixer of claim 41, wherein the dual port transistors are HEMTs.

48. The power mixer of claim 41, wherein the dual port transistors form a Gilbert cell scaled for power-handling capabilities.

49. The power mixer of claim 41, wherein the dual port transistors are preceded by a plurality of gain stages in a cascade configuration.

50. The power mixer of claim 41, wherein the versions of the in-phase (I) component and the quadrature (Q) component comprise direct versions of the in-phase (I) component and the quadrature (Q) component.

51. The power mixer of claim 41, wherein the versions of the in-phase (I) component and the quadrature (Q) component comprise direct and inverted versions of the in-phase (I) component and the quadrature (Q) component.

52. A method of amplifying a baseband signal for transmission as an amplified RF signal, the method comprising:

providing signals at a baseband centered frequency to a relatively high impedance input of a quadrature mixer that are versions of an in-phase (I) component and a quadrature (Q) component representing the baseband signal;

amplifying a reference signal;

providing the amplified reference signal at an RF frequency to a predetermined low impedance input of the quadrature mixer;

simultaneously performing a final stage of amplification and modulation of the versions of the in-phase (I) component and the quadrature (Q) component with the quadrature mixer using the amplified reference signal;

combining the modulated and amplified versions of the in-phase (I) component and the quadrature (Q) component to form the amplified RF signal; and

optimizing power conversion efficiency during the combination with a combining circuit.

53. The method of claim 52, further comprises the initial act of tuning the combining circuit to increase output power conversion efficiency and reduce the appearance of amplifier output harmonics.

54. The method of claim 52, further comprising providing gain to the reference signals prior to the final stage of modulation and amplification.

55. The method of claim 52, further comprising generating direct versions of the in-phase (I) component and the quadrature (Q) component.

56. The method of claim 52, further comprising generating direct and inverted versions of the in-phase (I), component and the quadrature (Q) component.