Quadrature gain and phase imbalance correction in a receiver

• US 20030053563A1
• Filed: 11/01/2002
• Published: 03/20/2003
• Est. Priority Date: 08/10/2001
• Status: Active Grant

• Current Assignee: Rishi Mohindra
• Original Assignee: Rishi Mohindra
• Inventors: Mohindra, Rishi
• Granted Patent: US 7,035,341 B2
• Time in Patent Office: Days
• 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 27/3809 Amplitude regulation arrangements

Abstract

The present invention offers a low cost, reliable, on chip implementation that takes advantage of circuitry already present in receivers to calibrate and correct for gain and phase errors in a transciever device. The present invention employs a digital signal processor along with multiple phase shifters and all pass networks to ensure proper levels of quadrature signals within the transciever. An internally generated double sideband suppressed carrier signal is created to produce the calibration signals used by the digital signal processor.

Claims

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

adjusting a phase angle to determine a peak amplitude for the in-phase component of the received signal;

adjusting the phase angle to determine a peak amplitude for the quadrature component of the received signal;

adjusting the phase angle to set the amplitudes for the in-phase and quadrature components of the received signal to be approximately equal at the same time; and

adjusting a second phase angle so that the in-phase and quadrature components of the received signal are 90 degrees out of phase.

2. The method of claim 1, wherein the second phase angle is adjusted by using a look-up table.

3. The method of claim 2, wherein the lookup table contains mathematical solutions to an equation.

4. The method of claim 3, wherein the second phase angle is adjusted iteratively by a digital signal processing chip.

19. The method of claim 3, further comprising the act of coupling the double side band suppressed carrier signal to a receiver'"'"'s RF path at a low noise amplifier input terminal.

5. A communications device for correcting imbalance between in-phase and quadrature components of a signal comprising:

a first mixer to multiply a low frequency signal and high frequency signal to produce a double side-band suppressed carrier signal;

a second and third mixer to produce in-phase and quadrature components of the received signal from the double side-band suppressed carrier signal; and

a digital signal processor that controls both a calibration and correction mode for determining and correcting phase errors within the signal paths of the communications device.

6. The communication device of claim 5, wherein the digital signal processor varies the phases of the I and Q signal to determine a gain adjustment.

7. The communication device of claim 6, wherein the digital signal processor changes the signal levels of the I and Q branches so that they are equal to each other.

8. The communication device of claim 7, wherein the digital signal processor enacts the correction mode after the calibration mode.

9. The communication device of claim 8, wherein the digital signal processor acesses a look-up table to correct for a phase error imbalance between the I and Q branch signals.

10. The communication device of claim 8, wherein the digital signal processor iteratively adjusts the phase difference between the I and Q brach signals until there is no phase error.

20. The communication device of claim 5 further compromising a means to couple double side band suppressed signal to the communications devices'"'"' RF path at a low noise amplifier input terminal.

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

producing I and Q branch calibration signals wherein the I branch signal is represented by;

I(t)=A.(1+Δ

G/2).Sin(ω

_BB.t+Δ

φ

_BB/2).Cos(θ

_RF), and the Q branch signal is represented by;

Q(t)=A.(1−

Δ

G/2).Sin(ω

_BB.t−

Δ

φ

_BB/2).Sin(θ

_RF−

Δ

φ

_RF);

varying the gains of the I and Q branches until Δ

G=0;

varying θ

_RF over a range greater than π

/2 and record the maximum I and Q signal levels over this range of θ

_RF;

adjusting the DSB-SC phase shift so that I and Q signal levels are exactly equal at the same time and measure their corresponding rms levels so that Cos(θ

_RF)=Sin(θ

_R−

Δ

φ

_RF)=A<sub>Δ

φ

RF</sub>;

using the measured level of A<sub>Δ

φ

RF</sub> to find the corresponding IQ phase error Δ

φ

_RF in a look-up table; and

shifting the relative phase between the in-phase and quadrature components of the received signal to be 90 degrees, by adjusting the phase error based on the amount stored in the look-up table.

12. The method of claim 11, wherein the I and Q branch signals are produced by calibration tones such as a double side band suppressed carrier signal.

13. The method of claim 11, wherein a digital signal processor varies the gains of the I and Q branches.

14. The method of claim 11, wherein a digital signal processor controls a phase shifter to vary θ

_RF.

15. The method of claim 14, wheren the digital signal processor controls a second phase shifter to adjust Δ

φ

_RF as determined from the look-up table.

16. A radio transceiver comprising:

an antenna;

a quadrature receiver for receiving signals and converting the received signals into in-phase baseband and a quadrature baseband signals;

a digital signal processor for performing the following tasks;

determining an imbalance in the quadrature receiver between the inphase and quadrature signals of the test signal under varying conditions,

generating a correction factor for at least some of the varying conditions; and

applying one or more correction factors to subsequently received inphase and quadrature baseband signals depending on a current condition to minimize an imbalance between the subsequently received inphase and quadrature baseband signals.

17. The radio receiver in claim 16, wherein one of the varying conditions is a changing gain of the baseband signals.

18. The radio receiver in claim 17, wherein one of the varying conditions is changing the phase relationship between baseband signals.