Adjusting a receiver

• US 20030012305A1
• Filed: 06/28/2002
• Published: 01/16/2003
• Est. Priority Date: 06/29/2001
• Status: Active Grant

• Current Assignee: Nokia Technologies Oy (Nokia Corporation)
• Original Assignee: Nokia Corporation
• Inventors: Auranen, Tommi
• Granted Patent: US 7,233,629 B2
• Time in Patent Office: Days
• US Class Current: 375/316
• CPC Class Codes: H03D 2200/0047 Offset of DC voltage or frequency
• CPC Class Codes: H03D 7/165 at least two frequency changers being located in different paths, e.g. in two paths with carriers in quadrature combined with amplitude demodulation H03D1/2245, combined with angle demodulation H03D3/007; N-path filters H03H19/002
• CPC Class Codes: H03J 2200/29 Self-calibration of a receiver
• CPC Class Codes: H04L 27/3863 Compensation for quadrature error in the received signal

Abstract

The invention relates to a method for adjusting IQ-imbalance of a direct conversion receiver (200). In the method a radio frequency training signal is locally generating and conveyed to an in-phase branch and a quadrature-phase branch of the receiver (200). The method comprises mixing, in the analogue domain, the radio frequency training signal of the in-phase branch with a first mixing signal to form a baseband in-phase component (I) of the training signal and mixing, in the analogue domain, the radio frequency training signal of the quadrature-phase branch with a second mixing signal to form a phase shifted component (Q) of the training signal. The baseband in-phase component (I) and phase shifted component (Q) are analogue-to-digital converted to form a digital baseband in-phase component and a digital baseband phase shifted component of the training signal. In the method the digital baseband in-phase and phase shifted components of the training signal are analyzed, in a digital demodulator (210), so as to detect the IQ-imbalance of the direct conversion receiver (200). The IQ-imbalance is corrected, based on the analysis, in the analogue domain.

Claims

1. A method for adjusting IQ-imbalance of a direct conversion receiver the method comprising:

locally generating a radio frequency training signal;

conveying in the analogue domain the radio frequency training 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, the radio frequency training signal of the in-phase branch with a first mixing signal to form a baseband in-phase component of the training signal and mixing, in the analogue domain, the radio frequency training signal of the quadrature-phase branch with a second mixing signal to form a phase shifted component of the training signal;

analogue-to-digital converting the baseband in-phase component of the training signal and the baseband phase shifted component of the training signal to form a digital baseband in-phase component of the training signal and a digital baseband phase shifted component of the training signal;

analysing, in the digital domain, the digital baseband in-phase and phase shifted components of the training signal so as to detect the IQ-imbalance; and

correcting the IQ-imbalance, based on the analysis, in the analogue domain.

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

analysing the phase difference between the digital baseband in-phase and phase shifted components of the training signal;

correcting an IQ-phase imbalance of the direct conversion receiver based on the analysis.

3. A method according to claim 1 or claim 2, wherein the method comprises:

analysing whether the phase difference between the digital baseband in-phase and phase shifted components of the training signal is 90 degrees;

correcting an IQ-phase imbalance of the direct conversion receiver based on the analysis.

4. A method according to claim 3, wherein the analysis of whether the phase difference between the digital baseband in-phase and phase shifted components of the training signal is 90 degrees is performed by analysing whether the other of the digital baseband components has a peak value when the other of the digital baseband components has zero or centre value.

5. A method according to any of the claims 2 to 4, wherein a correction of an IQ-phase imbalance is made so as to achieve a 90 degrees phase difference between a future baseband in-phase component and a future baseband phase shifted component.

6. A method according to any of the preceding claims, wherein the radio frequency training signal is a sinusoidal signal.

7. A method according to any of the preceding claims, wherein the first mixing signal is a local oscillator signal and the second mixing signal is a phase shifted local oscillator signal.

8. A method according to any of the preceding claims, wherein the second mixing signal is phase shifted by substantially 90 degrees with respect to the first mixing signal.

9. A method according to any of the preceding claims, 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.

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

generating, based on the detected IQ-imbalance, a control signal; and

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

11. A method according to any of the preceding claims, wherein the direct conversion receiver is a broadband receiver located in a mobile communication device so as to form a portable hand-held device.

12. A method according to any of the preceding claims, wherein the direct conversion receiver is selected from a group consisting of:

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

13. A method according to any of the preceding claims, wherein an IQ-amplitude imbalance is corrected based on the analysis of the digital baseband in-phase and phase shifted components of the training signal.

14. A method according to claim 13, wherein the correction of the IQ-amplitude imbalance is performed by adjusting the gain of at least one of the in-phase and quadrature-phase branches of the direct conversion receiver.

15. A method according to claim 14, wherein the gain of at least one of the in-phase and quadrature-phase branches of the direct conversion receiver is adjusted by an automatic gain control.

19. A communication device according to claim 18, wherein the communication device comprises, in addition to the direct conversion receiver, a cellular network interface for communicating information with a cellular network.

16. A method for adjusting IQ-imbalance of a direct conversion receiver the method comprising:

locally generating a training signal;

conveying the training signal to an in-phase branch of the direct conversion receiver and to a quadrature-phase branch of the direct conversion receiver;

using the training signal to correct the IQ-imbalance.

17. A direct conversion receiver comprising:

a training signal generator for generating a radio frequency training signal;

an in-phase branch and a quadrature-phase branch 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, the radio frequency training signal of the in-phase branch with a first mixing signal to form a baseband in-phase component of the training signal and second mixer for mixing, in the analogue domain, the radio frequency training signal of the quadrature-phase branch with a second mixing signal to form a phase shifted component of the training signal;

means for analogue-to-digital converting the baseband in-phase component of the training signal and the baseband phase shifted component of the training signal to form a digital baseband in-phase component of the training signal and a digital baseband phase shifted component of the training signal;

a digital demodulator for analysing, in the digital domain, the digital baseband in-phase and phase shifted components of the training signal so as to detect an IQ-imbalance, the direct conversion receiver being adapted to correct the IQ-imbalance, based on the analysis, in the analogue domain.

18. A communication device comprising a direct conversion receiver for correcting an IQ-imbalance, the direct conversion receiver comprising:

a training signal generator for generating a radio frequency training signal;

an in-phase branch and a quadrature-phase branch 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, the radio frequency training signal of the in-phase branch with a first mixing signal to form a baseband in-phase component of the training signal and second mixer for mixing, in the analogue domain, the radio frequency training signal of the quadrature-phase branch with a second mixing signal to form a phase shifted component of the training signal;

means for analogue-to-digital converting the baseband in-phase component of the training signal and the baseband phase shifted component of the training signal to form a digital baseband in-phase component of the training signal and a digital baseband phase shifted component of the training signal;

a digital demodulator for analysing, in the digital domain, the digital baseband in-phase and phase shifted components of the training signal so as to detect an IQ-imbalance, the direct conversion receiver being adapted to correct the IQ-imbalance, based on the analysis, in the analogue domain.

20. A system comprising a transmitter and a 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 training signal generator for generating a radio frequency training signal;

an in-phase branch and a quadrature-phase branch 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, the radio frequency training signal of the in-phase branch with a first mixing signal to form a baseband in-phase component of the training signal and second mixer for mixing, in the analogue domain, the radio frequency training signal of the quadrature-phase branch with a second mixing signal to form a phase shifted component of the training signal;

means for analogue-to-digital converting the baseband in-phase component of the training signal and the baseband phase shifted component of the training signal to form a digital baseband in-phase component of the training signal and a digital baseband phase shifted component of the training signal;

a digital demodulator for analysing, in the digital domain, the digital baseband in-phase and phase shifted components of the training signal so as to detect an IQ-imbalance, the direct conversion receiver being adapted to correct the IQ-imbalance, based on the analysis, in the analogue domain.