IQ-imbalance

• US 7,336,730 B2
• Filed: 06/25/2002
• Issued: 02/26/2008
• Est. Priority Date: 06/29/2001
• Status: Expired due to Fees

• Current Assignee: Nokia Corporation
• Original Assignee: Nokia Corporation
• Inventors: Kajava, Juha, Auranen, Tommi
• Primary Examiner(s): Tran; Khanh C.
• Application Number:
  US10/482,254
• Publication Number:
  US 20040156450A1
• Time in Patent Office: 2,072 Days
• Field of Search: 375/298, 375/316, 375/285, 375/322, 375/260, 375/345, 455/296, 455/324, 455/255, 455/326, 455/334, 455/337
• US Class Current: 375/316
• CPC Class Codes: H03D 3/009 Compensating quadrature phase or amplitude imbalances
• CPC Class Codes: H04B 1/30 for homodyne or synchrodyne receivers demodulator circuits H03D1/22
• CPC Class Codes: H04L 2027/0016 Stabilisation of local oscillators
• CPC Class Codes: H04L 27/26524 Fast Fourier transform [FFT] or discrete Fourier transform [DFT] demodulators in combination with other circuits for demodulation

Abstract

The invention relates to a method for correcting an IQ-imbalance (In-phase and Quadrature) of an IQ-based direct conversion receiver (200). In the method a group of radio frequency pilot signals are received in the direct conversion receiver (200). They are conveyed to an in-phase branch and a quadrature-phase branch of the receiver (200) and mixed, in the analogue domain, to form a baseband in-phase (I) and quadrature-phase (Q) signal components. The signal componets are conveyed to a digital demodulator (210) which detects the IQ-phase imbalance of the direct conversion receiver (200) by analysing at least one of the baseband in-phase (I) and the quadrature-phase (Q) signal components. In the method, the detected IQ-imbalance is corrected, in the analogue domain of the direct conversion receiver (200), to achieve a 90 degrees phase difference between a future baseband in-phase (I) signal component and a future baseband quadrature-phase (Q) signal component.

Claims

1. A method for correcting an IQ-imbalance (In-phase and Quadrature) of an IQ-based direct conversion receiver the method comprising:

receiving a radio frequency signal in the direct conversion receiver, the radio frequency signal being received from an antenna;

conveying, in an analogue domain of the direct conversion receiver, the received radio frequency signal to an in-phase branch of the direct conversion receiver and to a quadrature-phase branch of the direct conversion receiver;

mixing, in the analogue domain of the direct conversion receiver, the radio frequency signal of the in-phase branch with a first mixing signal to form a baseband in-phase (I) signal component and mixing the radio frequency signal of the quadrature-phase branch with a second mixing signal to form a baseband quadrature-phase (Q) signal component;

conveying the baseband in-phase (I) signal component and the baseband quadrature-phase (Q) signal component to a digital demodulator;

detecting, in the digital demodulator, the IQ-imbalance of the direct conversion receiver by analysing at least one of the baseband in-phase (I) or quadrature-phase (Q) signal components;

correcting the IQ-imbalance, detected in the digital demodulator, in the analogue domain of the direct conversion receiver to achieve at least close to a 90 degrees phase difference between a future baseband in-phase signal component and a future baseband quadrature-phase signal component.

2. A method according to claim 1, wherein the received radio frequency signal comprises a group of pilot signals, the method comprising:

detecting the IQ-imbalance based on the group of pilot signals.

3. A method according to claim 2, wherein the method comprises:

detecting the IQ-imbalance by analysing at least one of the baseband in-phase (I) or quadrature-phase (Q) signal components of the group of pilot signals.

4. A method according to claim 2, wherein the method comprises:

averaging the baseband quadrature-phase (Q) signal component of the group of pilot signals;

detecting the IQ-imbalance by finding out whether the averaged baseband quadrature-phase (Q) signal component of the group of pilot signals has the value of zero.

5. A method according to claim 1, wherein the method comprises:

analogue-to-digital converting the baseband in-phase (I) signal component and the baseband quadrature-phase (Q) signal component to form a digital baseband in-phase signal component and a digital baseband quadrature-phase signal component;

detecting the IQ-imbalance of the direct conversion receiver by analysing at least one of the digital baseband in-phase or quadrature-phase signal components.

6. A method according to claim 1, wherein the first mixing signal is a local oscillator signal and the second mixing signal is a phase shifted local oscillator signal.

7. A method according to claim 1, wherein the second mixing signal is substantially in a 90 degrees phase shift compared to the first mixing signal.

8. A method according to claim 1, wherein the second mixing signal is generated from the first mixing signal by shifting the phase of the first mixing signal in an adjustable phase shifter.

9. A method according to claim 8, wherein the method comprises:

generating within the digital demodulator, based on the detected IQ-imbalance, a correction signal; and

correcting the phase shift of the adjustable phase shifter with the aid of the correction signal so as to correct the IQ-imbalance of the direct conversion receiver.

10. A method according to claim 1, wherein the direct conversion receiver is a broadband receiver located in a mobile communication device so as to form a portable hand-held device.

11. A method according to claim 1, wherein the direct conversion receiver is one of the following:

a DVB-T (Digital Video Broadcasting-Terrestrial) direct conversion receiver, an ISDB-T (Integrated Services Digital Broadcasting-Terrestrial) direct conversion receiver.

12. An IQ-based (In-phase and Quadrature) direct conversion receiver for correcting an IQ-imbalance the direct conversion receiver comprising:

a radio frequency part for receiving a radio frequency signal in the direct conversion receiver, the radio frequency signal being received from an antenna;

an in-phase branch and a quadrature-phase branch, in an analogue domain of the direct conversion receiver, for conveying the received radio frequency signal in the in-phase branch and the quadrature-phase branch;

a first mixer for mixing, in the analogue domain of the direct conversion receiver, the radio frequency signal of the in-phase branch with a first mixing signal to form a baseband in-phase (I) signal component and second mixer for mixing, in the analogue domain of the direct conversion receiver, the radio frequency signal of the quadrature-phase branch with a second mixing signal to form a baseband quadrature-phase (Q) signal component;

a digital demodulator adapted to receive the baseband in-phase (I) signal component and the baseband quadrature-phase (Q) signal component, the digital demodulator being adapted to detect the IQ-imbalance of the direct conversion receiver by analysing at least one of the baseband in-phase (I) or quadrature-phase (Q) signal components; and

means for correcting the IQ-imbalance, detected in the digital demodulator, in the analogue domain of the direct conversion receiver to achieve at least close to a 90 degrees phase difference between a future baseband in-phase signal component and a fixture baseband quadrature-phase signal component.

13. A communication device comprising an IQ-based (In-phase and Quadrature) direct conversion receiver for correcting an IQ-imbalance the direct conversion receiver comprising:

a radio frequency part for receiving a radio frequency signal in the direct conversion receiver, the radio frequency signal being received from an antenna;

an in-phase branch and a quadrature-phase branch, in an analogue domain of the direct conversion receiver, for conveying the received radio frequency signal in the in-phase branch and the quadrature-phase branch;

a first mixer for mixing, in the analogue domain of the direct conversion receiver, the radio frequency signal of the in-phase branch with a first mixing signal to form a baseband in-phase (I) signal component and second mixer for mixing, in the analogue domain of the direct conversion receiver, the radio frequency signal of the quadrature-phase branch with a second mixing signal to form a baseband quadrature-phase (Q) signal component;

a digital demodulator adapted to receive the baseband in-phase (I) signal component and the baseband quadrature-phase (Q) signal component, the digital demodulator being adapted to detect the IQ-imbalance of the direct conversion receiver by analysing at least one of the baseband in-phase (I) or quadrature-phase (Q) signal components; and

means for correcting the IQ-imbalance, detected in the digital demodulator, in the analogue domain of the direct conversion receiver to achieve at least close to a 90 degrees phase difference between a future baseband in-phase signal component and a future baseband quadrature-phase signal component.

14. A communication device according to claim 13, wherein the communication device comprises, in addition to the direct conversion receiver, a cellular network interface for communicating information with a cellular network.

15. A system comprising a transmitter and an IQ-based (In-phase and Quadrature) direct conversion receiver for correcting an IQ-imbalance, the transmitter comprising a modulator for transmitting a radio frequency signal to the direct conversion receiver the direct conversion receiver comprising:

a radio frequency part for receiving the radio frequency signal in the direct conversion receiver, the radio frequency signal being received from an antenna;

an in-phase branch and a quadrature-phase branch, in an analogue domain of the direct conversion receiver, for conveying the received radio frequency signal in the in-phase branch and the quadrature-phase branch;

a first mixer for mixing, in the analogue domain of the direct conversion receiver, the radio frequency signal of the in-phase branch with a first mixing signal to form a baseband in-phase (I) signal component and second mixer for mixing, in the analogue domain of the direct conversion receiver, the radio frequency signal of the quadrature-phase branch with a second mixing signal to form a baseband quadrature-phase (Q) signal component;

a digital demodulator adapted to receive the baseband in-phase (I) signal component and the baseband quadrature-phase (Q) signal component, the digital demodulator being adapted to detect the IQ-imbalance of the direct conversion receiver by analysing at least one of the baseband in-phase (I) or quadrature-phase (Q) signal components;

means for correcting the IQ-imbalance, detected in the digital demodulator, in the analogue domain of the direct conversion receiver to achieve at least close to a 90 degrees phase difference between a future baseband in-phase signal component and a future baseband quadrature-phase signal component.