Digital communication receiver with digital, IF, I-Q balancer

• US 6,442,217 B1
• Filed: 05/22/2000
• Issued: 08/27/2002
• Est. Priority Date: 05/22/2000
• Status: Expired due to Term

• Current Assignee: Tamiras Per Pte Ltd LLC (Intellectual Ventures LLC)
• Original Assignee: SiCOM, Inc. (Renesas Electronics Corporation)
• Inventors: Cochran, Bruce A.
• Primary Examiner(s): TSE, YOUNG TOI
• Application Number:
  US09/576,220
• Time in Patent Office: 827 Days
• Field of Search: 375/229, 375/231, 375/232, 375/326, 375/327, 375/346, 375/348, 375/279, 375/281, 375/329, 375/332, 329/304, 329/307, 329/308
• US Class Current: 375/326
• CPC Class Codes: H04L 2027/0036 using a recovered symbol clock
• CPC Class Codes: H04L 2027/0038 using an equaliser
• CPC Class Codes: H04L 27/3863 Compensation for quadrature error in the received signal

Abstract

A communication system (10) includes a transmitter (12) which induces in a communication signal (16), a first component of in-phase to quadrature phase (I-Q) imbalance and a receiver (14) which adds a second component of I-Q imbalance. A digital, intermediate frequency (IF) I-Q balancer (38) compensates for the receiver-induced I-Q imbalance so that total distortion is sufficiently diminished and a data directed carrier tracking loop (60) may then perform carrier synchronization to generate a baseband signal (70). An adaptive equalizer (64) within the carrier tracking loop (60) may then effectively operate to compensate for additional distortions, such as the transmitter-induced I-Q imbalance.

Claims

1. A digital communication receiver comprising:

an analog downconversion section which provides a complex, digitized, intermediate frequency (IF) communication signal exhibiting an in-phase to quadrature phase (I-Q) imbalance;

an I-Q balancer having a signal input adapted to receive said IF communication signal and having an output which provides a locally balanced IF communication signal; and

a carrier tracking loop having an input adapted to receive said locally balanced IF communication signal, wherein said carrier tracking loop converts said locally balanced IF communication signal into a baseband communication signal, and said carrier tracking loop has an equalizer that equalizes said baseband communication signal.

2. A digital communication receiver as claimed in claim 1 wherein said I-Q balancer comprises an asymmetric equalizer.

3. A digital communication receiver as claimed in claim 1 wherein said I-Q balancer comprises a memoryless equalizer.

4. A digital communication receiver as claimed in claim 1 wherein said carrier tracking loop is a data directed feedback loop.

5. A digital communication receiver as claimed in claim 1 wherein:

said IF communication signal conveys data at a symbol rate;

said I-Q balancer has a control input which receives a data stream responsive to said locally balanced IF communication signal, said data stream being updated at least at said symbol rate; and

said I-Q balancer compensates said IF communication signal in response to a plurality of coefficients which are updated at least at said symbol rate in response to said data stream.

6. A digital communication receiver as claimed in claim 5 additionally comprising an interpolator having an input coupled to said output of said I-Q balancer and an output coupled to said control input of said I-Q balancer, said interpolator providing symbol synchronization for said digital communication receiver.

7. A digital communication receiver as claimed in claim 6 wherein said interpolator provides non-data directed symbol synchronization.

8. A digital communication receiver as claimed in claim 5 wherein said data stream is a complex data stream having in-phase and quadrature phase components, and said I-Q balancer comprises:

a first coefficient generator which revises a first one of said plurality of coefficients and is responsive to said in-phase components from said data stream;

a second coefficient generator which revises a second one of said plurality of coefficients and is responsive to said quadrature phase components from said data stream; and

a third coefficient generator which revises a third one of said plurality of coefficients and is responsive to a cross product of said in-phase and quadrature phase components from said data stream.

9. A digital communication receiver as claimed in claim 8 wherein each of said first, second and third coefficient generators is additionally responsive to a magnitude expressed by pairs of said in-phase and quadrature phase components from said data stream.

10. A digital communication receiver as claimed in claim 8 wherein:

said first coefficient generator revises said first coefficient for a future unit interval in response to said first coefficient for a past unit interval;

said second coefficient generator revises said second coefficient for said future unit interval in response to said second coefficient for said past unit interval; and

said third coefficient generator revises said third coefficient for said future unit interval in response to said third coefficient for said past unit interval.

11. A method of processing an input communication signal in a digital communication receiver, said input communication signal exhibiting a transmitter-induced, in-phase to quadrature phase (I-Q) imbalance, said method comprising:

downconverting said input communication signal to produce a digital, complex, intermediate frequency (IF) communication signal in a manner which adds a local I-Q imbalance to said transmitter-induced I-Q imbalance;

balancing said IF communication signal to compensate for said local I-Q imbalance and to generate a locally balanced IF communication signal;

generating a baseband communication signal from said locally balanced IF communication signal; and

equalizing said baseband communication signal to compensate for said transmitter-induced I-Q imbalance.

12. A method as claimed in claim 11 wherein said equalizing step additionally compensates for intersymbol interference.

13. A method as claimed in claim 11 additionally comprising forming a non-data directed feedback loop to achieve symbol synchronization prior to said equalizing step.

14. A method as claimed in claim 11 wherein said generating step comprises forming a data directed feedback loop to achieve carrier synchronization.

15. A method as claimed in claim 14 wherein:

said forming step comprises the step of interpolating said locally balanced IF communication signal to generate a symbol-synchronized IF communication signal; and

said balancing step comprises generating a plurality of coefficients in response to said symbol-synchronized IF communication signal.

16. A method as claimed in claim 15 wherein said symbol-synchronized IF communication signal is expressed as a complex data stream having in-phase and quadrature phase components, and said coefficient-generating step comprises:

revising a first one of said plurality of coefficients in response to said in-phase components from said data stream;

revising a second one of said plurality of coefficients in response to said quadrature phase components from said data stream; and

revising a third one of said plurality of coefficients in response to a cross product of said in-phase and quadrature phase components from said data stream.

17. A digital communication receiver which receives an input communication signal exhibiting a transmitter-induced in-phase to quadrature phase (I-Q) imbalance, said digital communication receiver comprising:

an analog downconversion section that receives said input communication signal and produces an unbalanced, complex, IF digital communication signal in which a local I-Q imbalance has been added to said transmitter-induced I-Q imbalance;

an I-Q balancer having an input adapted to receive said unbalanced, complex, IF digital communication signal and having an output which provides a locally balanced IF communication signal compensated for said local I-Q imbalance; and

a carrier tracking loop having an input adapted to receive said locally balanced IF communication signal, said carrier tracking loop converting said locally balanced IF communication signal into a baseband communication signal, and said carrier tracking loop having a baseband equalizer that balances said transmitter-induced I-Q imbalance of said input communication signal.

18. A digital communication receiver as claimed in claim 17 wherein said carrier tracking loop is a data directed feedback loop.

19. A digital communication receiver as claimed in claim 17 wherein said I-Q balancer has a control input, and said receiver additionally comprises an interpolator having an input coupled to said output of said I-Q balancer and an output coupled to said control input of said I-Q balancer, said interpolator providing non-data directed symbol synchronization for said digital communication receiver.

20. A digital communication receiver as claimed in claim 17 wherein said I-Q balancer comprises:

an asymmetric equalizer having a signal input which receives said unbalanced, complex, IF digital communication signal, having an output which provides said locally balanced IF communication signal, and having coefficient inputs; and

a coefficient generation section having a control input responsive to said locally balanced IF communication signal and coefficient outputs coupled to said coefficient inputs of said asymmetric equalizer.