Calibration of I-Q balance in transceivers

• US 20030223480A1
• Filed: 03/04/2003
• Published: 12/04/2003
• Est. Priority Date: 03/04/2002
• Status: Active Grant

• Current Assignee: Red Rock Analytics, LLC
• Original Assignee: John H. Cafarella
• Inventors: Cafarella, John H.
• Granted Patent: US 7,346,313 B2
• Time in Patent Office: Days
• US Class Current: 375/219
• CPC Class Codes: H04B 1/30 for homodyne or synchrodyne receivers demodulator circuits H03D1/22
• CPC Class Codes: H04L 2027/0016 Stabilisation of local oscillators
• CPC Class Codes: H04L 2027/0022 using the carrier of the associated receiver of a transceiver
• CPC Class Codes: H04L 27/364 Arrangements for overcoming imperfections in the modulator, e.g. quadrature error or unbalanced I and Q levels
• CPC Class Codes: H04L 27/3863 Compensation for quadrature error in the received signal
• CPC Class Codes: H04L 5/16 Half-duplex systems; Simplex/duplex switching; Transmission of break signals non-automatically inverting the direction of transmission

Abstract

Transceivers using direct conversion between baseband and RF have become popular for low-cost designs. Bandwidth-efficient modulations employ information on both phases of the carrier, and for high-order signaling alphabets, it becomes problematic to realize Direct-Conversion transceivers for which adequate gain balance between I and Q channels throughout the transmit and receive chains. For heterodyne transceivers I-Q balance is often less of an issue, by contrast, because most of the required gain operates at an Intermediate Frequency. In both cases, the trend toward lower supply voltages further exacerbates this problem because of the poorer control of analog parameters at low voltage. The present invention addresses this difficulty via a calibration method and system in which a calibration signal is generated in the transmit stage and injected into the receive stage so that any mismatches in gain can be observed and corrected.

Claims

1. A transceiver system for transmitting and receiving data using both I and Q channels, comprising:

a transmit chain;

a receive chain; and

a calibration subsystem comprising a signal path for injecting the a calibration signal, generated in response to and as a function of a signal generated through the transmit chain, into the receive chain of the transceiver in order to independently calibrate the I-Q gain balance of the both transmit and receive chains in their entirety

2. A transceiver system according to claim 1, wherein the calibration signal originates at baseband in the transmit channel, and is observed at baseband in the receive channel.

3. A transceiver system according to claim 1, wherein the transceiver is a direct-conversion transceiver.

4. A transceiver system according to claim 1, wherein the transceiver is a heterodyne-conversion transceiver.

5. A transceiver system according to claim 1, further including a channel gain adjuster for varying the differential I-Q gain in the transmit and receive chains independently in response to the calibration signal being injected into the receiver chain.

6. A transceiver system according to claim 1, further including a channel gain adjuster for varying the differential I-Q gain in the imbalanced chain in response to the calibration signal being injected into the receiver chain.

7. A transceiver system comprising:

A. a transmit chain including;

a signal generator for generating a baseband transmit signal;

baseband I-Q amplification subsystem for providing baseband amplification of the baseband transmit signal;

a direct-conversion subsystem for converting the baseband transmit signal to an RF transmit signal, and an RF transmit signal port;

B. a receive chain including;

an RF receive port for receiving an RF receive signal;

a direct-conversion subsystem for converting the RF receive signal to a baseband receive signal;

a baseband I-Q amplification subsystem for providing amplification of the baseband receive signal;

a processor for processing of the baseband receive signal as required for the normal function of the transceiver, and

C. a calibration subsystem including;

a calibration RF signal generator for generating a calibration RF signal as a baseband transmit signal;

a signal path for injecting the calibration RF signal from the RF transmit signal port to the RF receive signal port;

a processor for processing the baseband receive calibration RF signal to form an observable indicator of I-Q imbalance; and

a channel gain adjuster for varying the differential I-Q gain in the transmit and receive chains independently.

8. A transceiver system according to claim 7, further including means for preventing the signal path for injecting the calibration RF signal from permanently imparting an unfavorable net phase shift from baseband transmit to baseband receive.

9. A transceiver system according to claim 8, wherein the means for preventing the signal path for injecting the calibration RF signal from permanently imparting an unfavorable net phase shift from baseband transmit to baseband receive includes a phase-calibration cycling subsystem.

10. A transceiver system according to claim 8, wherein the means for preventing the signal path for injecting the calibration RF signal from permanently imparting an unfavorable net phase shift from baseband transmit to baseband receive includes a slowly time-varying phase modulation subsystem.

11. A transceiver system according to claim 7, wherein the calibration RF signal includes a sequence of pulses taking on purely real or imaginary values at any instant.

12. A transceiver system according to claim 7, wherein the calibration RF signal includes a sampled phasor.

13. A transceiver system according to claim 7, wherein the calibration RF signal includes a discrete phasor.

14. A transceiver system according to claim 7, wherein the calibration RF signal includes a discrete phasor comprising jⁿ or j⁻

n.

15. A transceiver system according to claim 7, wherein the calibration RF signal includes a calibration cycle, and the calibration cycle determines the transmitter I-Q gain settings which minimize the observable indicator while holding the receive I-Q gain settings constant, and which in turn determines the receiver I-Q gain settings which minimizes the observable indicator while holding the transmit I-Q gain settings constant.

16. A transceiver system according to claim 7, wherein the calibration RF signal includes successive calibration cycles, and successive calibration cycles are used to refine or maintain I-Q balance.

17. A transceiver system comprising:

A. a transmit chain including;

a signal generator for generating a baseband transmit signal;

baseband I-Q amplification subsystem for providing baseband amplification of the baseband transmit signal;

direct-conversion subsystem for converting the baseband transmit signal to an RF transmit signal, and including an RF transmit signal port;

B. a receive chain including;

an RF receive port for receiving an RF receive signal;

direct-conversion subsystem for converting the RF receive signal to a baseband receive signal;

baseband I-Q amplification subsystem for providing amplification of the baseband receive signal;

processing of the baseband receive signal as required for the normal function of the transceiver, and

C. a calibration subsystem including;

a calibration RF signal generator for generating a calibration RF signal as a baseband transmit signal;

a signal path for injecting the calibration RF signal from the RF transmit signal port to the RF receive signal port;

a processor for processing the baseband receive calibration RF signal to form an observable indicator of I-Q imbalance; and

, channel gain adjuster for varying the differential I-Q gain in the imbalanced chain.

18. A transceiver system according to claim 17, wherein the calibration RF signal includes a sequence of pulses taking on purely real or imaginary values at any instant.

19. A transceiver system according to claim 17, wherein the calibration RF signal includes a sampled phasor.

20. A transceiver system according to claim 17, wherein the calibration RF signal includes a discrete phasor.

21. A transceiver system according to claim 17, wherein the calibration RF signal includes a discrete phasor comprising jⁿ or j⁻

n.

22. A transceiver system according to claim 17, wherein successive calibration cycles are used to refine or maintain I-Q balance.

23. A transceiver system comprising:

A. a transmit chain including;

a signal generator for generating a baseband transmit signal;

a baseband I-Q amplification subsystem for providing baseband amplification of the baseband transmit signal;

at least one stage of frequency conversion of the baseband transmit signal to an intermediate frequency;

conversion subsystem for converting the baseband transmit signal at the intermediate frequency to an RF transmit signal, and including an RF transmit signal port;

B. a receive chain including;

an RF receiving port for receiving an RF receive signal;

at least one stage of frequency conversion of the receive signal to an intermediate frequency;

a conversion subsystem for converting the RF receive signal to a baseband receive signal;

baseband I-Q amplification subsystem for providing amplification of the baseband receive signal;

processing of the baseband receive signal as required for the normal function of the transceiver, and

C. a calibration subsystem including;

a calibration RF signal generator for generating a calibration RF signal as a baseband transmit signal;

a signal path for injecting the calibration RF signal from the RF transmit signal port to the RF receive signal port;

a processor for processing the baseband receive calibration RF signal to form an observable indicator of I-Q imbalance; and

,

channel gain adjuster for varying the differential I-Q gain in the transmit and receive chains independently.

24. A transceiver system according to claim 23, further including means for preventing the signal path for injecting the calibration RF signal from permanently imparting an unfavorable net phase shift from baseband transmit to baseband receive.

25. A transceiver system according to claim 24, wherein the means for preventing the signal path for injecting the calibration RF signal from permanently imparting an unfavorable net phase shift from baseband transmit to baseband receive includes a phase-calibration cycling subsystem.

26. A transceiver system according to claim 24, wherein the means for preventing the signal path for injecting the calibration RF signal from permanently imparting an unfavorable net phase shift from baseband transmit to baseband receive includes a slowly time-varying phase modulation subsystem.

27. A transceiver system according to claim 23, wherein the calibration RF signal includes a sequence of pulses taking on purely real or imaginary values at any instant.

28. A transceiver system according to claim 23, wherein the calibration RF signal includes a sampled phasor.

29. A transceiver system according to claim 23, wherein the calibration RF signal includes a discrete phasor.

30. A transceiver system according to claim 23, wherein the calibration RF signal includes a discrete phasor comprising jⁿ or j⁻

n.

31. A transceiver system according to claim 23, wherein the calibration RF signal includes a calibration cycle, and the calibration cycle determines the transmitter I-Q gain settings which minimize the observable indicator while holding the receive I-Q gain settings constant, and which in turn determines the receiver I-Q gain settings which minimizes the observable indicator while holding the transmit I-Q gain settings constant.

32. A transceiver system according to claim 23, wherein the calibration RF signal includes successive calibration cycles, and successive calibration cycles are used to refine or maintain I-Q balance.

33. A transceiver system according to claim 23, wherein the at least one stage of frequency conversion includes amplification means for amplifying the transmit signal at the intermediate frequency.

34. A transceiver system comprising:

A. a transmit chain including;

a signal generator for generating a baseband transmit signal;

a baseband I-Q amplification subsystem for providing baseband amplification of the baseband transmit signal;

at least one stage of frequency conversion of the baseband transmit signal to an intermediate frequency;

a conversion subsystem for converting the baseband transmit signal at the intermediate frequency to an RF transmit signal, and including an RF transmit signal port;

B. a receive chain including;

an RF receiving port for receiving an RF receive signal;

at least one stage of frequency conversion of the receive signal to an intermediate frequency;

a conversion subsystem for converting the RF receive signal to a baseband receive signal;

baseband I-Q amplification subsystem for providing amplification of the baseband receive signal;

processing of the baseband receive signal as required for the normal function of the transceiver, and

C. a calibration subsystem including;

a calibration RF signal generator for generating a calibration RF signal as a baseband transmit signal;

a signal path for injecting the calibration RF signal from the RF transmit signal port to the RF receive signal port;

a processor for processing the baseband receive calibration RF signal to form an observable indicator of I-Q imbalance; and

,

channel gain adjuster for varying the differential I-Q gain in the imbalanced chain.

35. A transceiver system according to claim 34, wherein the calibration RF signal includes a sequence of pulses taking on purely real or imaginary values at any instant.

36. A transceiver system according to claim 34, wherein the calibration RF signal includes a sampled phasor.

37. A transceiver system according to claim 34, wherein the calibration RF signal includes a discrete phasor.

38. A transceiver system according to claim 34, wherein the calibration RF signal includes a discrete phasor comprising j nor j n.

39. A transceiver system according to claim 34, wherein successive calibration cycles are used to refine or maintain I-Q balance.

40. A method of calibrating a transceiver system for transmitting and receiving data using both I and Q channels and including a transmit chain and a receive chain;

the method comprising;

injecting a calibration RF signal, generated in response to and as a function of a signal generated through the transmit chain, into the receive chain of the transceiver in order to independently calibrate the I-Q gain balance of the both transmit and receive chains in their entirety

41. A method according to claim 40, wherein the calibration RF signal originates at baseband in the transmit channel, and is observed at baseband in the receive channel.

42. A method according to claim 40, wherein the transceiver is a direct-conversion transceiver.

43. A method according to claim 40, wherein the transceiver is a heterodyne-conversion transceiver.

44. A method according to claim 40, further including adjusting the channel gain so as to vary the differential I-Q gain in the transmit and receive chains independently in response to the calibration RF signal being injected into the receiver chain.

45. A method according to claim 40, further including adjusting the channel gain so as to vary the differential I-Q gain in the imbalanced chain in response to the calibration RF signal being injected into the receiver chain.

46. A method of calibrating a transceiver system for transmitting and receiving data using both I and Q channels and comprising (a) a transmit chain including a signal generator for generating a baseband transmit signal;

baseband I-Q amplification subsystem for providing baseband amplification of the baseband transmit signal;

direct-conversion subsystem for converting the baseband transmit signal to an RF transmit signal, and including an RF transmit signal port; and

(b) a receive chain including an RF receive port for receiving an RF receive signal;

direct-conversion subsystem for converting the RF receive signal to a baseband receive signal;

baseband I-Q amplification subsystem for providing amplification of the baseband receive signal;

a processor for processing of the baseband receive signal as required for the normal function of the transceiver, the method comprising;

generating a calibration RF signal as a baseband transmit signal; and

injecting the calibration RF signal from the RF transmit signal port to the RF receive signal port;

processing the baseband receive calibration RF signal to form an observable indicator of I-Q imbalance; and

varying the differential I-Q gain in the transmit and receive chains independently.

47. A method according to claim 46, further including preventing the injection of the calibration RF signal from permanently imparting an unfavorable net phase shift from baseband transmit to baseband receive.

48. A method according to claim 47, wherein preventing the injection of the calibration RF signal from permanently imparting an unfavorable net phase shift from baseband transmit to baseband receive includes phase-calibration cycling.

49. A method according to claim 47, wherein preventing the injection of the calibration RF signal from permanently imparting an unfavorable net phase shift from baseband transmit to baseband receive includes slowly time-varying phase modulating.

50. A method according to claim 46, wherein generating the calibration RF signal includes generating a sequence of pulses taking on purely real or imaginary values at any instant.

51. A method according to claim 46, wherein the calibration RF signal includes a sampled phasor.

52. A method according to claim 46, wherein the calibration RF signal includes a discrete phasor.

53. A method according to claim 46, wherein the calibration RF signal includes a discrete phasor comprising jⁿ or j⁻

n.

54. A method according to claim 46, wherein the calibration RF signal includes a calibration cycle, and further including using the calibration cycle so as to determine the transmitter I-Q gain settings so as to minimize the observable indicator while holding the receive I-Q gain settings constant, and determining the receiver I-Q gain settings so as to minimize the observable indicator while holding the transmit I-Q gain settings constant.

55. A method according to claim 46, wherein the calibration RF signal includes successive calibration cycles, and further including using the successive calibration cycles to refine or maintain I-Q balance.

56. A method of calibrating a transceiver system comprising (a) a transmit chain including a signal generator for generating a baseband transmit signal;

baseband I-Q amplification subsystem for providing baseband amplification of the baseband transmit signal;

a direct-conversion subsystem for converting the baseband transmit signal to an RF transmit signal, and an RF transmit signal port; and

(b) a receive chain including an RF receive port for receiving an RF receive signal;

a direct-conversion subsystem for converting the RF receive signal to a baseband receive signal;

baseband I-Q amplification subsystem for providing amplification of the baseband receive signal;

processing of the baseband receive signal as required for the normal function of the transceiver, the method comprising

generating a calibration RF signal as a baseband transmit signal;

injecting the calibration RF signal from the RF transmit signal port to the RF receive signal port;

processing the baseband receive calibration RF signal to form an observable indicator of I-Q imbalance; and

varying the differential I-Q gain in the imbalanced chain so as to adjust the gain.

57. A method according to claim 56, wherein generating the calibration RF signal includes generating a sequence of pulses taking on purely real or imaginary values at any instant.

58. A method according to claim 56, wherein the calibration RF signal includes a sampled phasor.

59. A method according to claim 56, wherein the calibration RF signal includes a discrete phasor.

60. A method according to claim 56, wherein the calibration RF signal includes a discrete phasor comprising jⁿ or j⁻

n.

61. A method according to claim 56, further including using successive calibration cycles to refine or maintain I-Q balance.

62. A method of calibrating a transceiver system comprising (a) a transmit chain including a signal generator for generating a baseband transmit signal;

a baseband I-Q amplification subsystem for providing baseband amplification of the baseband transmit signal;

at least one stage of frequency conversion of the baseband transmit signal to an intermediate frequency;

a conversion subsystem for converting the baseband transmit signal at the intermediate frequency to an RF transmit signal, and an RF transmit signal port; and

(b) a receive chain including an RF receiving port for receiving an RF receive signal;

at least one stage of frequency conversion of the receive signal to an intermediate frequency;

a conversion subsystem for converting the RF receive signal to a baseband receive signal;

baseband I-Q amplification subsystem for providing amplification of the baseband receive signal;

a processor for processing the baseband receive signal as required for the normal function of the transceiver, the method comprising

generating a calibration RF signal as a baseband transmit signal;

injecting the calibration RF signal from the RF transmit signal port to the RF receive signal port;

processing the baseband receive calibration RF signal to form an observable indicator of I-Q imbalance; and

varying the differential I-Q gain in the transmit and receive chains independently so as to adjust the differential I-Q gain so as to minimize any difference.

63. A method according to claim 62, further including preventing the injection of the calibration RF signal from permanently imparting an unfavorable net phase shift from baseband transmit to baseband receive.

64. A method according to claim 63, wherein preventing the injection of the calibration RF signal from permanently imparting an unfavorable net phase shift from baseband transmit to baseband receive includes a phase-calibration cycling.

65. A method according to claim 63, wherein preventing the injection of the calibration RF signal from permanently imparting an unfavorable net phase shift from baseband transmit to baseband receive includes slowly time-varying phase modulation.

66. A method according to claim 62, wherein the calibration RF signal includes a sequence of pulses taking on purely real or imaginary values at any instant.

67. A method according to claim 62, wherein the calibration RF signal includes a sampled phasor.

68. A method according to claim 62, wherein the calibration RF signal includes a discrete phasor.

69. A method according to claim 62, wherein the calibration RF signal includes a discrete phasor comprising jⁿ or j⁻

n.

70. A method according to claim 62, wherein the calibration RF signal includes a calibration cycle, wherein the method further includes using the calibration cycle to determine the transmitter I-Q gain settings which minimize the observable indicator while holding the receive I-Q gain settings constant, and determining the receiver I-Q gain settings which minimizes the observable indicator while holding the transmit I-Q gain settings constant.

71. A method according to claim 62, wherein the calibration RF signal includes successive calibration cycles, and the method further includes using successive calibration cycles to refine or maintain I-Q balance.

72. A method according to claim 62, wherein the at least one stage of frequency conversion includes amplification means for amplifying the transmit signal at the intermediate frequency.

73. A method of calibrating a transceiver system comprising:

(a) a transmit chain including;

a signal generator for generating a baseband transmit signal;

a baseband I-Q amplification subsystem for providing baseband amplification of the baseband transmit signal;

at least one stage of frequency conversion of the baseband transmit signal to an intermediate frequency;

a conversion subsystem for converting the baseband transmit signal at the intermediate frequency to an RF transmit signal, and an RF transmit signal port; and

(b) a receive chain including an RF receiving port for receiving an RF receive signal;

at least one stage of frequency conversion of the receive signal to an intermediate frequency;

a conversion subsystem for converting the RF receive signal to a baseband receive signal;

baseband I-Q amplification subsystem for providing amplification of the baseband receive signal; and

a processor for processing of the baseband receive signal as required for the normal function of the transceiver, the method comprising;

generating a calibration RF signal as a baseband transmit signal;

injecting the calibration RF signal from the RF transmit signal port to the RF receive signal port;

processing the baseband receive calibration RF signal to form an observable indicator of I-Q imbalance; and

,

varying the differential I-Q gain in the imbalanced chain so as to balance the I-Q gain.

74. A method according to claim 73, wherein the calibration RF signal includes a sequence of pulses taking on purely real or imaginary values at any instant.

75. A method according to claim 73, wherein the calibration RF signal includes a sampled phasor.

76. A method according to claim 73, wherein the calibration RF signal includes a discrete phasor.

77. A method according to claim 73, wherein the calibration RF signal includes a discrete phasor comprising jⁿ or j⁻

n.

78. A method according to claim 73, further including using successive calibration cycles to refine or maintain I-Q balance.