IQ-Imbalance

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.

1 - 11 . (canceled) 
   
   
       12 . An IQ-based (In-phase and Quadrature) 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; and   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 an IQ-imbalance of the direct conversion receiver by analysing at least one of the baseband in-phase (I) or quadrature-phase (Q) signal components, wherein   the direct conversion receiver is adapted to correct the IQ-imbalance, detected in the digital demodulator, in the analogue domain of the direct conversion receiver to achieve a 90 degrees phase difference or 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.   
   
   
       13 . A communication device comprising an IQ-based (In-phase and Quadrature) direct conversion receiver, 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; and   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 an IQ-imbalance of the direct conversion receiver by analysing at least one of the baseband in-phase (I) or quadrature-phase (Q) signal components, wherein   the direct conversion receiver is adapted to correct the IQ-imbalance, detected in the digital demodulator, in the analogue domain of the direct conversion receiver to achieve a 90 degrees phase difference or 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, 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; and   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 an IQ-imbalance of the direct conversion receiver by analysing at least one of the baseband in-phase (I) or quadrature-phase (Q) signal components, wherein   the direct conversion receiver is adapted to correct the IQ-imbalance, detected in the digital demodulator, in the analogue domain of the direct conversion receiver to achieve a 90 degrees phase difference or 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.   
   
   
       16 . A direct conversion receiver according to  claim 12 , wherein the direct conversion receiver is adapted to detect the IQ-imbalance based on a group of pilot signals comprised by the received radio frequency signal. 
   
   
       17 . A direct conversion receiver according to  claim 16 , wherein the direct conversion receiver is adapted to detect the IQ-imbalance by analysing at least one of the baseband in-phase (I) and quadrature-phase (Q) signal components of the group of pilot signals. 
   
   
       18 . A direct conversion receiver according to  claim 12 , wherein the direct conversion receiver comprises:
 an adjustable phase shifter for generating the second mixing signal from the first mixing signal by shifting the phase of the first mixing signal.   
   
   
       19 . A direct conversion receiver according to  claim 18 , wherein the digital demodulator is adapted to generate, based on the detected IQ-imbalance, a correction signal for correcting the phase shift of the adjustable phase shifter with the aid of the correction signal so as to correct the IQ-imbalance. 
   
   
       20 . A direct conversion receiver according to  claim 12 , wherein the direct conversion receiver is a broadband receiver. 
   
   
       21 . A communication device according to  claim 13 , wherein the communication device is a mobile communication device forming a portable hand-held device. 
   
   
       22 . An apparatus comprising:
 means for receiving a radio frequency signal in a direct conversion receiver, the radio frequency signal being received from an antenna;   means, 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;   means 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 means configured 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;   digital demodulator means for receiving the baseband in-phase (I) signal component and the baseband quadrature-phase (Q) signal component, said digital demodulator means being for detecting an IQ-imbalance of the direct conversion receiver by analyzing 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 means, in the analogue domain of the direct conversion receiver to achieve a 90 degrees phase difference or 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.   
   
   
       23 . An apparatus comprising:
 a circuit configured to receive baseband in-phase (I) and quadrature-phase signal components from a direct conversion circuit, the direct conversion circuit having formed the baseband in-phase (I) and quadrature-phase signal components by mixing, in an analogue domain of the direct conversion circuit, a radio frequency signal with first and second mixing signals, respectively, the radio frequency signal having been received from an antenna,   wherein the circuit is configured to detect an IQ-imbalance, including being configured to analyze at least one of the baseband in-phase (I) or quadrature-phase (Q) signal components, and   wherein the circuit is configured to generate a correction signal based on the detected IQ-imbalance, the circuit being further configured to feed the correction signal to the direct conversion circuit to correct the IQ-imbalance in the analogue domain to achieve a 90 degrees phase difference or at least close to a 90 degrees phase difference between future baseband in-phase and quadrature-phase signal components.   
   
   
       24 . An apparatus according to  claim 23 , wherein the circuit is configured to detect the IQ-imbalance based on a group of pilot signals comprised by the radio frequency signal. 
   
   
       25 . An apparatus according to  claim 24 , wherein the circuit being configured to detect the IQ-imbalance includes being configured to analyze at least one of the baseband in-phase (I) or quadrature-phase (Q) signal components of the group of pilot signals. 
   
   
       26 . An apparatus according to  claim 23 , wherein the circuit is configured to feed the correction signal to an adjustable phase shifter of the direct conversion circuit, the adjustable phase shifter being configured to shift the phase of the first mixing signal based on the correction signal to thereby generate the second mixing signal.