Digital estimation and correction of I/Q mismatch in direct conversion receivers

• US 7,020,220 B2
• Filed: 06/18/2002
• Issued: 03/28/2006
• Est. Priority Date: 06/18/2002
• Status: Expired due to Fees

• Current Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: Hansen, Christopher James
• Primary Examiner(s): Patel, Jay K.
• Assistant Examiner(s): Vlahos, Sophia
• Application Number:
  US10/172,978
• Publication Number:
  US 20030231723A1
• Time in Patent Office: 1,379 Days
• Field of Search: 455313- 15, 455317- 18, 455323- 24, 455/334, 455337- 34, 455255- 65, 455/296, 455/115, 455307- 12, 375/261, 375/298, 375/295, 375/349, 375/316, 375/343
• US Class Current: 375/324
• CPC Class Codes: H04L 2027/0016 Stabilisation of local oscillators
• CPC Class Codes: H04L 2027/0024 at the receiver end
• CPC Class Codes: H04L 27/0014 Carrier regulation of chaotic carriers H04L27/001; for multicarrier receivers H04L27/2657

Abstract

An IQ receiver includes an estimator/compensator module to determine and correct IQ mismatch errors between the I and Q channels of the IQ receiver. The estimator module determines a phase compensation factor C₁ and an amplitude compensation factor C₂ based on a calibration signal that is injected into the analog front-end of the IQ receiver. A compensator module applies the phase correction factor C₁ and the amplitude correction factor C₂ to the baseband output of the Q channel in order to reduce any phase or amplitude errors between the I and Q channels. The estimator module and the compensator module can be efficiently implemented in a digital state machine, or processor, including a digital signal processor.

Claims

1. In an IQ receiver, a method of correcting mismatch errors between an I channel and a Q channel, the method comprising the steps of:

injecting a calibration signal into an input of said IQ receiver, to produce an I_N baseband signal and a Q_N baseband signal at an output of said IQ receiver;

determining an average power P_I of said I_N baseband signal, and an average power P_Q of said Q_N baseband signal;

determining a cross-correlation R_IQ between said I_N baseband signal and said Q_N baseband signal;

determining a phase compensation factor C₁ based on said average power P_I and said cross-correlation R_IQ, said phase compensation factor C₁ determined to compensate for any phase error between said I_N baseband signal and said Q_N baseband signal; and

determining an amplitude compensation factor C₂ based on said average power P_I, said average power P_Q, and said cross-correlation R_IQ, wherein C₂ is determined to compensate for any amplitude error between said I_N baseband signal and said Q_N baseband signal.

2. The method of claim 1, wherein said phase compensation factor C₁ is determined according to the following, $C_1=\frac{R_{\mathrm{IQ}}}{P_I}.$

3. The method of claim 1, wherein said amplitude compensation factor C₂ is determined according to the following, $C_2={[\frac{1}{P_I}}^{}$

PI⁢

PQ-RIQ2]-1.

4. The method of claim 1, wherein said step of injecting includes the step of injecting a noise signal into an analog front-end of said IQ receiver.

5. The method of claim 1, wherein said step of injecting includes the step of disengaging said input of said IQ receiver from an information bearing signal source, and thereby said calibration signal is noise generated by said IQ receiver.

6. The method of claim 1, further comprising the step of compensating an information-bearing Q baseband signal with said phase compensation factor C₁ and said amplitude compensation factor C₂.

7. The method of claim 6, wherein said step of compensating includes the steps of:

multiplying an information bearing I baseband signal by said compensation factor C₁ to produce a C₁·

I baseband signal;

subtracting said C₁·

I baseband signal from said information bearing Q baseband signal to produce a phase-compensated Q baseband signal; and

multiplying said phase-compensated Q baseband signal by said amplitude compensation factor C₂.

8. The method of claim 1, wherein said step of determining an average power P_I of said I_N baseband signal, and an average power P_Q of said Q_N baseband signal includes the steps of:

squaring said I_N baseband signal to produce a squared I_N baseband signal;

determining an average of said squared I_N baseband signal to produce said average power P_I;

squaring said Q_N baseband signal to produce a squared Q_N baseband signal; and

determining an average of said squared Q_N baseband signal to produce said average power P_Q.

9. The method of claim 8, wherein said step of determining a cross-correlation R_IQ between said I_N baseband signal and said Q_N baseband signal includes the steps of:

multiplying said I_N baseband signal with said Q_N baseband signal, to determine I_NQ_N; and

averaging said I_NQ_N to produce said cross-correlation factor R_IQ.

10. The method of claim 1, wherein said step of determining a phase compensation factor C₁ includes the steps of:

determining a reciprocal of said average power P_I to produce 1/P_I; and

multiplying 1/P_I with said cross-correlation R_IQ to produce said phase compensation factor C₁.

11. The method of claim 1, wherein said step of determining an amplitude compensation factor C₂ includes the steps of:

multiplying P_I with P_Q to determine P_IP_Q;

determining a square of said cross-correlation R_IQ to determine R_IQ²;

subtracting said R_IQ² from P_IP_Q to produce P_IP_Q−

R_IQ²;

determining a square root of (P_IP_Q−

R_IQ²);

multiplying said square root of (P_IP_Q−

R_IQ²) by a reciprocal of 1/P_I to produce 1/P_I·

SQRT (P_IP_Q−

R_IQ²); and

determining reciprocal of 1/P_I·

SQRT (P_IP_Q−

R_IQ²).

19. The method of claim 1, wherein said phase compensation factor C₁ is determined according to:

$C_1={\frac{R_{\mathrm{IQ}}}{P_I}<br><br>\left[\frac{1}{P_I}<br><br>\sqrt{P_I<br><br>P_Q-R_{\mathrm{IQ}}^2}\right]}^{-1}.$

20. The method of claim 1, wherein said phase compensation factor C₁ is determined according to:

$C_2=\left[\frac{1}{P_I}<br><br>\sqrt{P_I<br><br>P_Q-R_{\mathrm{IQ}}^2}\right].$

21. The method of claim 20, wherein said amplitude compensation factor C₂ is determined according to:

$C_2=\frac{-R_{\mathrm{IQ}}}{P_I}<br><br>\left[\frac{1}{P_I}<br><br>\sqrt{P_I<br><br>P_Q-R_{\mathrm{IQ}}^2}\right].$

12. An apparatus for correcting mismatch between an I channel path and a Q channel path of an IQ receiver based on a calibration input signal, said I channel path and said Q channel path outputing an I_N baseband signal and a Q_N baseband signal responsive to said calibration input signal, said apparatus comprising:

a compensator module coupled to an output of said I channel path and an output of said Q channel path, said compensator module configured to compensate said output of said Q channel path with a phase compensation factor C₁ and an amplitude compensation factor C₂;

an estimator module configured to generate said phase compensation factor C₁ and said amplitude compensation factor C₂ responsive to said I_N baseband signal and said Q_N baseband signal,

wherein said phase compensation factor C₁ is determined according to, $C_1=\frac{R_{\mathrm{IQ}}}{P_I};<br><br>$

wherein said amplitude compensation factor C₂ is determined according to, $C_2={\left[\frac{1}{P_I}<br><br>\sqrt{P_I<br><br>P_Q-R_{\mathrm{IQ}}^2}\right]}^{-1};<br><br>$

wherein,

P_I is an average power of said I_N baseband signal,

P_Q is an average power of said Q_N baseband signal, and

R_IQ is a cross-correlation between said I_N baseband signal and said Q_N baseband signal.

13. The apparatus of claim 12, wherein said compensator module includes:

a first digital multiplier configured to multiply said output of said I channel path by said phase compensation factor C₁;

a digital subtractor configured to subtract an output of said first digital multiplier from an output of said Q channel path; and

a second digital multiplier configured to multiply an output of said digital subtractor with said amplitude compensation factor C₂.

14. The apparatus of claim 12, wherein said estimator module includes:

a power detector module configured to determine an average power P_I of said I_N baseband signal and an average power P_Q of said Q_N baseband signal;

a cross-correlation module configured to determine a cross-correlation between said I_N baseband signal and said Q_N baseband signal;

a phase compensation module configured to determine said phase compensation factor C₁ based on said average power P_I and said cross-correlation factor R_IQ; and

an amplitude compensator module configured to determine said amplitude compensation factor C₂ based on said average power P_I, said average power P_Q, and said cross-correlation factor R_IQ.

15. The apparatus of claim 14, wherein said cross-correlation module includes a digital multiplier configured to multiply said I_N baseband signal with said Q_N baseband signal.

16. The apparatus of claim 14, wherein said phase compensator module includes a digital multiplier configured to multiply said cross-correlation factor R_IQ with a reciprocal of said average power P_I.

17. The apparatus of claim 14, wherein said amplitude compensation module includes:

a first digital multiplier configured to multiply said average power P_I with said average power P_Q;

a digital subtractor configured to subtract a square of said cross-correlation R_IQ from an output of said first digital multiplier;

means for determining a square root of an output of said digital substracter;

a second digital multiplier for multiplying an output of said means for determining a square root with a reciprocal of said average power P_I.

18. An IQ receiver, comprising:

a receiver input;

a local oscillator;

means for generating a calibration signal that is coupled to said receiver input;

an I channel path, coupled to said receiver input, said I channel path having a first mixer coupled to said local oscillator and a second input coupled to said receiver input, and a first analog-to-digital converter coupled to an output of said first mixer, said analog-to-digital converter generating an I_N baseband signal responsive to said calibration signal;

a Q channel path, coupled to said receiver input, said Q channel path having a second mixer coupled to said local oscillator and a second input coupled to said receiver input, and a second analog-to-digital converter coupled to an output of said second mixer, said analog-to-digital converter generating an Q_N baseband signal responsive to said calibration signal;

a compensator module coupled to an output of said I channel path and an output of said Q channel path, said compensator module configured to compensate said output of said Q channel path with a phase compensation factor C₁ and an amplitude compensation factor C₂;

an estimator module configured to generate said phase compensation factor C₁ and said amplitude compensation factor C₂ responsive to said I_N baseband signal and a Q_N baseband signal,

wherein said phase compensation factor C₁ is determined according to, $C_1=\frac{R_{\mathrm{IQ}}}{P_I};<br><br>$

wherein said amplitude compensation factor C₂ is determined according to, $C_2={\left[\frac{1}{P_I}<br><br>\sqrt{P_I<br><br>P_Q-R_{\mathrm{IQ}}^2}\right]}^{-1};<br><br>$

wherein,

P_I is an average power of said I_N baseband signal,

P_Q is an average power of said Q_N baseband signal, and

R_IQ is a cross-correlation between said I_N baseband signal and said Q_N baseband signal.