Mirror signal IQ-imbalance correction

1. A system comprising:

a low-IF receiver configured to be tunable for selected channels;

a synthesizer configured to produce a Test Signal in mirror frequencies for a selected channel and for conveying the Test Signal to the receiver;

an IQ Imbalance Estimator configured for estimating a phase imbalance and a gain imbalance in the receiver based on a signal produced in the receiver from the Test Signal; and

a power detector configured to produce a Power Estimate of the signal produced in the receiver from the conveyed Test Signal,

wherein the system is further configured for:

setting a first searching region for gain imbalance and phase imbalance in the receiver;

selecting a first plurality of grid-points within the first searching region; and

measuring a Power Estimate for each grid-point in the first plurality of grid-points by setting a gain-correction and a phase-correction in the receiver corresponding to the coordinates of each grid-point in the first plurality of grid-points.

2. The system of claim 1 , wherein the first searching region is a two-dimensional space defined by gain imbalance values on a gain axis and phase imbalance values on a phase axis.

3. The system of claim 1 , wherein the system is further configured for:

measuring the Power Estimate of the signal produced in the receiver from the conveyed mirror-frequency signal for each grid-point in the first plurality of grid-points.

4. The system of claim 1 , further comprising:

an IQ Imbalance Compensator configured for adjusting the difference in the gain and the phase between the I channel and the Q channel in the receiver based on the estimated gain imbalance and the estimated phase imbalance.

5. The system of claim 1 , wherein the Test Signal is a single-tone signal in a mirror frequency.

6. The system of claim 1 , wherein the system is further configured for:

setting a second searching region within the first searching region, wherein the second searching region is a subset of the first searching region, and wherein the location of the second searching region is based on the measured Power Estimates for grid-points in the first plurality of grid-points.

7. The system of claim 6 , wherein the system is further configured for:

selecting a second plurality of grid-points within the second searching region; and

measuring a Power Estimate for each grid-point in the second plurality of grid-points by setting a gain-correction and a phase-correction in the receiver corresponding to the coordinates of each grid-point in the second plurality of grid-points and measuring the Power Estimate of the signal produced in the receiver from the conveyed mirror-frequency signal for each grid-point in the second plurality of grid-points.

8. The system of claim 1 , wherein the system is further configured such that the location of the second searching region within the first searching region is selected based on at least a location of a minimum-power grid-point, wherein the minimum-power grid-point is a grid-point in the first plurality of grid points with the smallest measured Power Estimate.

9. The system of claim 1 , wherein the system is further configured such that selecting the location of the second searching region within the first searching region further comprises:

estimating a power at the center of each grid adjacent to the minimum-power grid-point by averaging the power at the four corner grid-points of each of the adjacent grids;

setting the center of the second searching region to be the average of the coordinates of the minimum-power grid-point and the coordinates of the center of the grid with the smallest estimated power at the center.

10. A method comprising:

selecting a channel in a low-IF receiver;

producing a Test Signal in mirror frequencies for the selected channel;

conveying the Test Signal to the low-IF receiver;

estimating a phase imbalance and a gain imbalance in the receiver based on a signal produced in the low-IF receiver from the Test Signal;

measuring a Power Estimate of the signal produced in the low-IF receiver from the conveyed Test Signal;

estimating the phase imbalance and the gain imbalance in the low-IF receiver based on the Power Estimate;

varying the gain in the baseband section of the low-IF receiver such that the level of gain when measuring the Power Estimate for a first plurality of grid-points is lower than the level of gain when measuring the Power Estimate for a second plurality of grid-points; and

adjusting the difference in the gain and the phase between the I channel and the Q channel in the receiver based on the estimated gain imbalance and the estimated phase imbalance.

11. The method of claim 10 , further comprising:

setting a first searching region for gain imbalance and phase imbalance in the receiver, wherein the first searching region is a two-dimensional space defined by gain imbalance values on a gain axis and phase imbalance values on a phase axis;

selecting a first plurality of grid-points within the first searching region; and

measuring a Power Estimate for each grid-point in the first plurality of grid-points by setting a gain-correction and a phase-correction in the receiver corresponding to the coordinates of each grid-point in the first plurality of grid-points and measuring the Power Estimate of the signal produced in the receiver from the conveyed mirror-frequency signal for each grid-point in the first plurality of grid-points.

12. The method of claim 11 , further comprising:

setting a second searching region within the first searching region, wherein the second searching region is a subset of the first searching region, and wherein the location of the second searching region is based on the measured Power Estimates for grid-points in the first plurality of grid-points;

selecting a second plurality of grid-points within the second searching region; and

measuring a Power Estimate for each grid-point in the second plurality of grid-points by setting a gain-correction and a phase-correction in the receiver corresponding to the coordinates of each grid-point in the second plurality of grid-points and measuring the Power Estimate of the signal produced in the receiver from the conveyed mirror-frequency signal for each grid-point in the second plurality of grid-points.

13. The method of claim 10 , further comprising:

selecting the location of the second searching region within the first searching region based on at least a location of a minimum-power grid-point, wherein the minimum-power grid-point is a grid-point in the first plurality of grid points with the smallest measured Power Estimate.

14. An apparatus comprising:

a low-IF receiver configured to be tunable for selected channels;

a synthesizer configured to produce a Test Signal in mirror frequencies for a selected channel and for conveying the Test Signal to the receiver;

a power detector configured to produce a Power Estimate of the signal produced in the receiver from the conveyed Test Signal;

an IQ Imbalance Estimator configured for estimating a phase imbalance and a gain imbalance in the receiver based on a signal produced in the receiver from the Test Signal; and

an IQ Imbalance Compensator,

wherein the apparatus is further configured for:

setting a first searching region for gain imbalance and phase imbalance in the receiver, wherein the first searching region is a two-dimensional space defined by gain imbalance values on a gain axis and phase imbalance values on a phase axis;

selecting a first plurality of grid-points within the first searching region; and

measuring a Power Estimate for each grid-point in the first plurality of grid-points by setting a gain-correction and a phase-correction in the receiver corresponding to the coordinates of each grid-point in the first plurality of grid-points.

15. The apparatus of claim 14 , wherein the apparatus is further configured for:

setting a second searching region within the first searching region, wherein the second searching region is a subset of the first searching region, and wherein the location of the second searching region is based on the measured Power Estimates for grid-points in the first plurality of grid-points.

16. The apparatus of claim 14 , wherein the apparatus is further configured for:

selecting a second plurality of grid-points within the second searching region.

17. The apparatus of claim 14 , wherein the apparatus is further configured for:

measuring a Power Estimate for each grid-point in the second plurality of grid-points by setting a gain-correction and a phase-correction in the receiver corresponding to the coordinates of each grid-point in the second plurality of grid-points and measuring the Power Estimate of the signal produced in the receiver from the conveyed mirror-frequency signal for each grid-point in the second plurality of grid-points.

18. The apparatus of claim 14 , wherein the apparatus is further configured such that the location of the second searching region within the first searching region is selected based on at least a location of a minimum-power grid-point.

19. The apparatus of claim 14 , wherein the minimum-power grid-point is a grid-point in the first plurality of grid points with the smallest measured Power Estimate.