Closed loop transmitter IQ calibration

• US 8,175,549 B2
• Filed: 10/17/2008
• Issued: 05/08/2012
• Est. Priority Date: 10/17/2008
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Faust, Roi, Lerner, Gregory, Tal, Nir
• Primary Examiner(s): Nguyen, Simon
• Application Number:
  US12/253,410
• Publication Number:
  US 20100099363A1
• Time in Patent Office: 1,299 Days
• Field of Search: 455/76.11, 455/67.13, 455/67.14, 455/67.16, 455/67.7, 455/91, 4551142-1152, 455126-1272, 455/67.11, 375296-298
• US Class Current: 455/91
• CPC Class Codes: H04B 17/10 of transmitters
• CPC Class Codes: H04B 17/21 for calibration; for correcting measurements

Abstract

A novel and useful apparatus for and method of closed loop IQ calibration for use in a transmitter. The IQ calibration mechanism functions to provide calibration of IQ imbalance in the presence of real world RF impairments. An iterative process is used to update the gain and phase mismatch values whereby the metrics are calculated in a differential manner without the need for calculation absolute imbalance values. At each iteration, updating the gain and phase mismatch estimate requires only the direction of the correction to be determined. The direction of the correction is calculated using only the differences between output power measurements. The updated gain and phase mismatch estimates are used to update an IQ correction matrix. This process is repeated until a desired stopping criterion is reached. Gear shifting is used to ensure quick convergence of the algorithm while providing the ability to achieve any desired level of accuracy.

Claims

1. A method of IQ calibration for use in a radio frequency (RF) transmitter, said method comprising the steps of:

transmitting a plurality of calibration signals and detecting a corresponding power output to generate a plurality of power detection signals thereby;

estimating a gain mismatch and a phase mismatch based on differences of said plurality of power detection signals;

updating an IQ correction matrix based on said gain mismatch estimate and said phase mismatch estimate; and

repeating said steps of transmitting, detecting, estimating and updating until a desired convergence is reached,

wherein said plurality of power detection signals comprises;

a first power signal P₁=α

²;

a second power signal P₂=1;

a third power signal

2. The method according to claim 1, wherein said plurality of calibration signals comprise:

a first tone transmitted only on an I path;

a second tone transmitted only on a Q path;

a third tone transmitted only on both I and Q paths; and

a complex conjugate of said third tone.

3. The method according to claim 1, wherein said step of estimating uses an initial estimate of zero for both gain and phase mismatch.

4. The method according to claim 1, wherein said step of estimating said gain mismatch comprises calculating the difference P₁-P₂.

5. The method according to claim 1, wherein said step of estimating said phase mismatch comprises calculating the difference P₃-P₄.

6. The method according to claim 1, further comprising the step of applying said updated correction matrix to predistortion of data prior to transmission.

7. The method according to claim 1, further comprising the step of applying gear shifting to said step of estimating thereby providing quick convergence while minimizing residual error.

8. A method of IQ calibration for use in a radio frequency (RF) transmitter, said method comprising the steps of:

transmitting a plurality of calibration signals and measuring a corresponding power output to generate a plurality of power measurement signals thereby;

first determining a first direction of correction for a gain mismatch estimate as a function of a first difference of said power measurement signals and generating an updated gain mismatch estimate therefrom;

second determining a second direction of correction for a phase mismatch estimate as a function of a second difference of said power measurement signals and generating an updated phase mismatch estimate therefrom;

updating an IQ correction matrix in accordance with said updated gain mismatch estimate and said updated phase mismatch estimate; and

repeating said steps of transmitting, first determining, second determining, and updating until a stopping criterion is reached,

wherein said plurality of power detection signals comprises;

a first power signal P₁=α

²;

a second power signal P₂=1;

a third power signal

9. The method according to claim 8, wherein said plurality of calibration signals comprise:

a first tone transmitted only on an I path;

a second tone transmitted only on a Q path;

a third tone transmitted only on both I and Q paths; and

a complex conjugate of said third tone.

10. The method according to claim 8, wherein an initial gain mismatch estimate and initial phase mismatch estimate of zero are used in said steps of first determining and second determining.

11. The method according to claim 8, wherein said first direction is determined based on the difference between said first power signal and said second power signal.

12. The method according to claim 8, wherein said second direction is determined based on the difference between said third power signal and said fourth power signal.

13. The method according to claim 8, further comprising the step of applying said updated correction matrix to predistortion of data prior to transmission.

14. The method according to claim 8, further comprising the step of applying gear shifting to said step of estimating thereby providing quick convergence while minimizing residual error.

15. An apparatus for IQ calibration for use in a radio frequency (RF) transmitter, comprising:

a calibration signal module operative to transmit a plurality of calibration signals;

a power detector operative to detect a power at an output of said transmitter

in response to said calibration signals and to generate a plurality of power detection signals thereby;

a correction matrix module operative to;

update a gain mismatch estimate and a phase mismatch estimate in accordance with differences between said power detection signals; and

iteratively update an IQ correction matrix in accordance with updated gain and phase mismatch estimates

wherein said plurality of power detection signals comprises;

a first power signal P₁=α

²;

a second power signal P₂=1;

a third power signal

16. The apparatus according to claim 15, wherein said plurality of calibration signals comprise:

a first tone transmitted only on an I path;

a second tone transmitted only on a Q path;

a third tone transmitted only on both I and Q paths; and

a complex conjugate of said third tone.

17. The apparatus according to claim 15, further comprising a predistortion module operative to apply said updated correction matrix to predistortion of data prior to transmission.

18. The apparatus according to claim 15, wherein said correction matrix module is operative to apply gear shifting to update said gain and phase mismatch estimates thereby providing quick convergence while minimizing residual error.

19. The apparatus according to claim 15, wherein said correction matrix module is operative to update said gain mismatch based on the difference between said first power signal and said second power signal.

20. The apparatus according to claim 15, wherein said correction matrix module is operative to update said phase mismatch based on the difference between said third power signal and said fourth power signal.

21. A radio frequency (RF) transmitter, comprising:

a digital baseband operative to generate a digital baseband signal;

digital to analog converter operative to convert said digital baseband signal to an analog baseband signal;

an upconverter operative to translate said analog baseband signal to a higher transmit frequency;

a power amplifier operative to amplify said upconverted signal for transmission over an RF channel;

a power detector operative to measure a power output of said power amplifier; and

said digital baseband comprising an IQ calibration module operative to;

transmit a plurality of calibration signals;

generate a plurality of power detection signals in response to the power output of said power amplifier in response to said calibration signals;

update a gain mismatch estimate and a phase mismatch estimate in accordance with differences between said power detection signals; and

iteratively update an IQ correction matrix in accordance with updated gain and phase mismatch estimates,

wherein said plurality of power detection signals comprises;

a first power signal P₁=α

²;

a second power signal P₂=1;

a third power signal

22. The transmitter according to claim 21, wherein said plurality of calibration signals comprise:

a first tone transmitted only on an I path;

a second tone transmitted only on a Q path;

a third tone transmitted only on both I and Q paths; and

a complex conjugate of said third tone.

23. The transmitter according to claim 21, wherein said digital baseband is further operative to apply said updated correction matrix to predistortion of data prior to transmission.

24. The transmitter according to claim 21, wherein said IQ calibration module is operative to apply gear shifting to update said gain and phase mismatch estimates thereby providing quick convergence while minimizing residual error.

25. A communications device, comprising:

at least one radio comprising a transmitter;

said transmitter comprising an IP calibration module, said IP calibration module comprising;

a calibration signal module operative to transmit a plurality of calibration signals;

a power detector operative to detect a power at an output of said transmitter in response to said calibration signals and to generate a plurality of power detection signals thereby;

a correction matrix module operative to;

update a gain mismatch estimate and a phase mismatch estimate in accordance with differences between said power detection signals; and

iteratively update an IQ correction matrix in accordance with updated gain and phase mismatch estimates,

wherein said plurality of power detection signals comprises;

a first power signal P₁=α

²;

a second power signal P₂=1;

a third power signal

26. The communications device according to claim 25, wherein said plurality of calibration signals comprise:

a first tone transmitted only on an I path;

a second tone transmitted only on a Q path;

a third tone transmitted only on both I and Q paths; and

a complex conjugate of said third tone.

27. The communications device according to claim 25, wherein said digital baseband is further operative to apply said updated correction matrix to predistortion of data prior to transmission.

28. The communications device according to claim 25, wherein said correction matrix module is operative to apply gear shifting to update said gain and phase mismatch estimates thereby providing quick convergence while minimizing residual error.