Calibration method for the correction of in-phase quadrature signal mismatch in a radio frequency transceiver

• US 20050148304A1
• Filed: 12/24/2003
• Published: 07/07/2005
• Est. Priority Date: 12/24/2003
• Status: Abandoned Application

• Current Assignee: Fodus Communications, Inc.
• Original Assignee: Fodus Communications, Inc.
• Inventors: Jerng, Albert Chia-Wen
• Application Number:
  US10/746,586
• Publication Number:
  US 20050148304A1
• Time in Patent Office: Days
• US Class Current: 455/75
• CPC Class Codes: H04B 1/30 for homodyne or synchrodyne receivers demodulator circuits H03D1/22

Abstract

A method is disclosed to correct the IQ mismatch of an RF transceiver. The method generates a reference signal down a transmitting-receiving loop and measures the received signals S_DTA-1 and S_DTA-2, respectively dominated by their desired component and image component, under two programmed mixer settings of operating mode and LOF. The method then calculates a system image rejection ratio (IRR_sys) with S_DTA-1 and S_DTA-2, systematically adjusts the amplitude and phase pre-distortion of the transmitting baseband signals till IRR_sys is maximized thus correcting for the transmitter IQ mismatch. The now-corrected transmitter IQ mismatch is then used to correct receiver IQ mismatch by reprogramming the first setting and measuring mismatches in amplitude ΔA and phase Δφ between received baseband IQ signals, corrects for ΔA and Δφ accordingly and stores the corrective values for future compensation of receiver IQ mismatch. The systematic pre-distortion can be implemented using a look-up table or analytical calculation.

Claims

1. A calibration method for correcting amplitude and phase mismatch between in-phase and quadrature signals, called IQ mismatch, in a radio frequency transceiver (RFXVR) having a transmitting path and a receiving path, the method comprising:

a. generating a baseband reference signal S_REF at frequency f_REF that results in, through the transmitting path, a transmitting RF-signal;

b. coupling said transmitting RF-signal through the receiving path thereby yielding a data signal S_DTA having a desired component S_DSR at frequency f_DSR and an undesired image signal S_IMG at frequency f_IMG; and

c. iteratively programming the RFXVR until a corresponding ratio k=S_DSR/S_IMG is maximized thereby minimizing the undesirable effect due to IQ mismatch essentially from a transmitting upper sideband mixer (TX USB mixer) of the transmitting path.

2. The method of claim 1 wherein said ratio k is further expressed in a logarithmic power domain so as to correspond to a system image rejection ratio (IRR) of IRR_sys=20×

Log₁₀(S_DSR/S_IMG).

6. The method of claim 1 further comprises, after step-c, the following steps to correct IQ mismatch from said RX USB/LSB mixer-2:

d. coupling said transmitting RF-signal to RX mixer-1 thereby yielding corresponding receiving baseband in-phase and quadrature signals (RX BD-I and RX BD-Q) along the receiving path having, due to IQ mismatch only from said RX USB/LSB mixer-2, a mismatch in amplitude Δ

A and phase Δ

φ

there between;

e. programming a setting as follows;

said f_LO2 equal to f_LO2-1; and

said RX USB/LSB mixer-2 in first operating mode generating said f_LO3 equal to f_LO3-1; and

f. calculating and correcting for said Δ

A and Δ

φ and

storing the respective corrective values for future correction of IQ mismatch due to said RX USB/LSB mixer-2.

7. The method of claim 6 wherein the correction for IQ mismatch is performed at system power on of the RFXVR.

8. The method of claim 7 wherein the correction for IQ mismatch is further performed periodically during idle time of the RFXVR.

11. The method of claim 1 wherein said receiving path further comprises a bandpass filter, having a pass frequency range from f_BP1 to f_BP2, for passing an in-band Intermediate Frequency (IF) signal while attenuating an out-band IF signal with a band pass rejection (BPR) of dB.

12. The method of claim 11 wherein said BPR is at least about 40 dB.

13. The method of claim 11 wherein said bandpass filter is a SAW (surface acoustic wave) filter.

14. The method of claim 11 wherein said f_BP1 and f_BP2, of said bandpass filter are about 366 MHz and about 382 MHz respectively.

15. The method of claim 1 wherein said TX USB mixer further comprises a first local oscillator (LO1) of frequency f_LO1 and exhibits an image rejection ratio of IRR₁ dB.

16. The method of claim 15 wherein said f_LO1 is about 1600 MHz.

17. The method of claim 16 wherein said f_REF is about 8 MHz.

18. The method of claim 17 wherein said f_LO3-1 is about 374 MHz and said f_LO2-1 is about f_LO1+f_LO3-1=1974 MHz thereby yielding an S_DSR-1 at frequency f_DSR˜

8 MHz and an S_IMG-1 at frequency f_IMG˜

8 MHz.

21. The method of claim 17 wherein said f_LO3-2 is about 358 MHz and said f_LO2-2 is about f_LO1+f_LO3-2=1958 MHz thereby yielding an S_DSR-2 at frequency f_DSR˜

8 MHz and an S_IMG-2 at frequency f_IMG˜

8 MHz.

22. The method of claim 21 wherein both said IRR₁ of the TX USB mixer and said IRR₂ of the RX USB/LSB mixer-2 are from about 20 dB to about 30 dB thereby causing said S_DSR-2 to be about 30 dB below said S_IMG-2.

3. The method of claim I wherein step-c further comprises:

c1. programming a first RFXVR setting thereby yielding a first data signal S_DTA-1 whose undesired image S_IMG-1 is sufficiently attenuated with respect to whose desired component S_DSR-1 making the signal power of S_DSR-1 essentially equal to that of S_DTA-1;

c2. programming a second RFXVR setting thereby yielding a second data signal S_DTA-2 whose desired component S_DSR-2 is sufficiently attenuated with respect to whose undesired image S_IMG-2 making the signal power of S_IMG-2 essentially equal to that of S_DTA-2; and

c3. repeating step-c1 and step-c2, each time after systematically pre-distorting at least the amplitude or the phase of at least one of pre-distorted transmitting baseband in-phase and quadrature signals (TX BD-I or TX BD-Q) along the transmitting path, until the ratio k=S_DTA-1/S_DTA-2 is maximized.

4. The method of claim 3 wherein the step of programming a first RFXVR setting further comprises the settings:

a second local oscillator (LO2) frequency f_LO2, being generated by a first programmable receiving mixer (RX mixer-1) of the receiving path, equal to a first value f_LO2-1; and

a second programmable upper sideband/lower sideband receiving mixer (RX USB/LSB mixer-2) in first operating mode generating a third local oscillator (LO3) frequency fLO3 equal to a first value f_LO3-1.

5. The method of claim 4 wherein the step of programming a second RFXVR setting further comprises the following settings:

said f_LO2 equal to a second value f_LO2-2; and

said RX USB/LSB mixer-2 in second operating mode generating said f_LO3 equal to a second value f_LO3-2.

9. The method of claim 3 wherein the step of systematically pre-distorting further comprises using a look-up table to set the amplitude and phase angle of at least one of said signals TX BD-I or TX BD-Q.

10. The method of claim 4 wherein said first operating mode is an LSB mode and said second operating mode is a USB mode.

19. The method of claim 4 wherein said RX USB/LSB mixer-2 exhibits an image rejection ratio of IRR₂ dB.

20. The method of claim 19 wherein both said IRR₁ of the TX USB mixer and said IRR₂ of the RX USB/LSB mixer-2 are from about 20 dB to about 30 dB thereby causing said S_IMG-1 to be about 40 dB to 60 dB below said S_DSR-1.