Method and apparatus for correcting phase and gain imbalance between in-phase (I) and quadrature (Q) components of a received signal based on a determination of peak amplitudes

• US 5,949,821 A
• Filed: 08/05/1996
• Issued: 09/07/1999
• Est. Priority Date: 08/05/1996
• Status: Expired due to Term

• Current Assignee: Intel Corporation
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Carter, Charles H., Emami, Shahriar
• Primary Examiner(s): Pham, Chi H.
• Assistant Examiner(s): LUTHER, WILLIAM A
• Application Number:
  US08/691,188
• Time in Patent Office: 1,128 Days
• Field of Search: 375/235, 375/232, 375/230, 375/229, 364/724.2, 364/724.19, 333/18 R, 333/28 T
• US Class Current: 375/235
• CPC Class Codes: H03D 3/008 Compensating DC offsets
• CPC Class Codes: H03D 3/009 Compensating quadrature phase or amplitude imbalances

Abstract

A communication device (100) includes an equalizer (126) for correcting imbalance between in-phase and quadrature components of a received signal. The equalizer (126) determines peak amplitude for the in-phase and quadrature components, and the phase imbalance between both components (440). At least one of the in-phase and quadrature components is adjusted based on a function of the phase imbalance, and of the ratio of peak amplitudes of the in-phase and quadrature components (450, 460).

Claims

1. A method for correcting imbalance between in-phase and quadrature components of a received signal, comprising the steps of:

determining peak amplitudes for the in-phase and quadrature components of the received signal;

determining phase imbalance between the in-phase and quadrature components of the received signal;

adjusting at least one of the in-phase and quadrature components, including the steps of;

selecting one of the in-phase and quadrature components as an unbalanced signal component, and another of the in-phase and quadrature components as a reference signal component;

scaling the unbalanced signal component by a scaling factor based on a ratio of peak amplitudes for the unbalanced and reference signal components;

scaling the reference signal component by a scaling factor of sin φ

;

applying a scaling factor of 1/cos φ

to a difference between the scaled reference signal component and the scaled unbalanced signal component;

adjusting amplitude of the at least one of the in-phase and quadrature components based on a difference in peak amplitudes between the in-phase and quadrature components; and

adjusting phase of the at least one of the in-phase and quadrature components using a function based on the phase imbalance.

2. In a communication device, a method comprising the steps of:

receiving a composite signal having modulated data;

separating the composite signal into in-phase and quadrature components;

determining a phase imbalance, φ

, between the in-phase and quadrature components;

selecting one of the in-phase and quadrature components as an unbalanced signal component, and another of in-phase and quadrature components as a reference signal component;

scaling the unbalanced signal component by a scaling factor based on a ratio of the reference signal component to the unbalanced signal component to obtain a first intermediate result;

scaling the reference signal component by a scaling factor of sin φ

to obtain a second intermediate result;

subtracting the second intermediate result from the first intermediate result to obtain a third intermediate result;

scaling the third intermediate result by a scaling factor of 1/cos φ

to obtain an adjusted unbalanced signal component; and

demodulating the reference signal component and the adjusted unbalanced signal component to recover modulated data.

3. A method for correcting imbalance between in-phase and quadrature components of a received signal, comprising the steps of:

obtaining a block of data digitally modulated to have an in-phase component and a quadrature component;

selecting one of the in-phase and quadrature components as an unbalanced signal component, y'"'"'(t), and another of in-phase and quadrature components as a reference signal component, r(t);

digitally processing the block of data, including the steps of;

detecting amplitude peaks for r(t) and y'"'"'(t), respectively, within the block of data;

averaging the amplitude peaks for r(t) to obtain a peak amplitude estimate, A;

averaging the amplitude peaks for y'"'"'(t) to obtain a peak amplitude estimate, A'"'"';

estimating phase imbalance, φ

, between r(t) and y'"'"'(t) , wherein;

##EQU5## where r(t)y'"'"'(t) represents cross-correlation between r(t) and y'"'"'(t); and

generating an adjusted quadrature component, y(t), wherein;

##EQU6##

4. The method of claim 3, wherein the step of selecting comprises the steps of:

selecting the quadrature component as the unbalanced signal component; and

selecting the in-phase component as the reference signal component.

5. A communication device having an equalizer for correcting imbalance between in-phase and quadrature components of a received signal, comprising:

a peak estimator that estimates peak amplitudes of the in-phase and quadrature components of the received signal;

a phase estimator that estimates phase imbalance between the in-phase and quadrature components of the received signal; and

an adjuster responsive to the in-phase and quadrature components to adjust amplitude of at least one of the in-phase and quadrature components based on a ratio of peak amplitudes of the in-phase and quadrature components, and to adjust phase of at least one of the in-phase and quadrature components based on phase imbalance between the in-phase and quadrature components;

wherein the equalizer operates on one of the in-phase and quadrature components as a reference signal, r(t), and another of the in-phase and quadrature components as an unbalanced signal, y'"'"'(t), using the phase imbalance to obtain a corrected quadrature component, y(t), such that;

##EQU7## where φ

is the phase imbalance, and A and A'"'"' are estimates for peak amplitudes of the in-phase and quadrature components, respectively.

6. The communication device of claim 5, wherein:

##EQU8## where r(t)y'"'"'(t) represents cross-correlation between r(t) and y'"'"'(t).

7. The communication device of claim 5, further comprising a demodulator, wherein the in-phase component and the corrected quadrature component are coupled as inputs to the demodulator.

8. A method for correcting imbalance between in-phase and quadrature components of a received signal, comprising the steps of:

determining peak amplitudes for the in-phase and quadrature components a block of data representing the received signal for a specific non-instantaneous duration of time, and isolating values identified with the respective peak amplitudes;

determining phase imbalance between the in-phase and quadrature components of the received signal, wherein the phase imbalance is derived from a function based at least in the isolated peak amplitude values for the in-phase and quadrature components of the received signal; and

adjusting at least one of the in-phase and quadrature components, including the steps of;

adjusting amplitude of the at least one of the in-phase and quadrature components over the block of data representing the received signal based on a difference between the isolated peak amplitudes values of the in-phase and quadrature components, but not based on other non-peak amplitude values corresponding to the block data representing the received signal; and

adjusting phase of the at least one of the in-phase and quadrature components using a function based on the phase imbalance.

9. A communication device having an equalizer for correcting imbalance between in-phase and quadrature components of a received signal, comprising:

a peak estimator that estimates peak amplitudes of the in-phase and quadrature components of a block of data representing the received signal for a specific non-instantaneous duration of time, and that isolates values identified with the respective peak amplitudes;

a phase estimator that estimates phase imbalance between the in-phase and quadrature components of the received signal, wherein the phase imbalance is derived from a function based at least in part on the isolated peak amplitude values for the in-phase and quadrature components of the received signal; and

an adjuster responsive to the in-phase and quadrature components to adjust amplitude of at least one of the in-phase and quadrature components over the block of data representing the received signal based on a ratio of the isolated peak amplitude values of the in-phase and quadrature components but not based on non-peak amplitude values corresponding to the block of data representing the received signal, and to adjust phase of at least one of the in-phase and quadrature components based only on phase imbalance between the in-phase and quadrature components.