Integrated circuit, wireless communication unit and method for determining quadrature imbalance
An integrated circuit comprising processing logic for operably coupling to radio frequency (RF) receiver circuitry arranged to receive a wireless network signal. The receiver circuitry generates in-phase and quadrature digital baseband representations of the wireless network signal. The processing logic determines quadrature (I/Q) imbalance of the RF receiver circuitry based on the in-phase and quadrature digital baseband representations of the wireless network signal.
1. An integrated circuit comprising: radio frequency (RF) receiver circuitry arranged to receive a wireless network signal, wherein the receiver circuitry generates in-phase and quadrature digital baseband representations of the wireless network signal; and
processing logic operably coupled to the radio frequency (RF) receiver circuitry and arranged to:
determine quadrature (I/Q) imbalance of the RF receiver circuitry based on the in-phase and quadrature digital baseband representations of the wireless network signal, wherein the processing logic is arranged to set the RF receiver circuitry to operate in a direct conversion radio (DCR) mode for the purpose of determining quadrature imbalance and determine quadrature imbalance only in the DCR mode; and
to set the RF receiver circuitry to operate in an intermediate frequency (I/F) mode when I/Q imbalance has been determined.
2. The integrated circuit of claim 1 , wherein the processing logic is arranged to calibrate the RF receiver circuitry to compensate for quadrature imbalance of the RF receiver circuitry.
3. The integrated circuit of claim 1 , wherein the processing logic is arranged to determine quadrature imbalance based on measurements of in-phase and quadrature digital baseband representations of a network signal received as part of a power scan operation.
4. The integrated circuit of claim 3 , wherein: the processing logic is further arranged to synchronise signal timing of a wireless communication unit containing the integrated circuit with a remote base station; and
the processing logic is arranged to determine quadrature imbalance prior to synchronisation with the remote base station.
5. The integrated circuit, of claim 1 , wherein the processing logic is arranged to determine quadrature imbalance based on measurements of in-phase and quadrature digital baseband representations of a network signal received as part of a frequency control channel (FCCh) scan.
6. The integrated circuit of claim 5 , wherein the processing logic is arranged to determine quadrature imbalance based on measurements of in-phase and quadrature digital baseband representations of a frequency correction burst (FCB) within the FCCh.
7. The integrated circuit of claim 1 , further comprising an RFIC control signal, whereby the processing logic is to signal the RF receiver circuitry via the RFIC control signal to operate in the DCR mode.
8. A method for determining quadrature (I/Q) imbalance within radio frequency (RF) receiver circuitry of a wireless communication unit, the method comprising the steps of:
receiving a wireless network signal;
setting a first signal generated by a local oscillator of the RF receiver circuitry to a first frequency for the purpose of measuring quadrature imbalance;
generating in-phase and quadrature digital baseband representations of the wireless network signal;
determining quadrature (I/Q) imbalance of the RF receiver circuitry based on the in-phase and quadrature digital baseband representations of the wireless network signal; and
setting a second signal generated by the local oscillator of the RF receiver circuitry to a second frequency for the purpose of normal operations, wherein the first frequency is not used for the purpose of normal operations.
9. The method of claim 8 further comprising calibrating the RF receiver circuitry to compensate for quadrature imbalance of the RF receiver circuitry in response to said determination.
10. The method of claim 8 further comprising setting the local oscillator of the RF receiver circuitry to generate the frequency of the first signal wherein the first signal, when mixed with the received wireless network signal, shifts a frequency of the received wireless network signal to a baseband frequency, thereby causing the RF receiver circuitry to operate in a direct conversion radio (DCR) mode prior to determining quadrature imbalance.
11. The method of claim 8 further comprising determining quadrature imbalance based on measurements of in-phase and quadrature digital baseband representations of a network signal received as part of a power scan operation.
12. The method of claim 8 further comprising determining quadrature imbalance based on measurements of in-phase and quadrature digital baseband representations of a network signal received as part of a frequency control channel (FCCh) scan.
13. The method of claim 12 further comprising determining quadrature imbalance based on measurements of in-phase and quadrature digital baseband representations of a frequency correction burst within the FCCh.
14. The method of claim 8 , wherein:
the RF receiver circuitry is operating in a very low intermediate frequency (VLIF) mode during normal operations;
the VLIF is a positive frequency; and
the setting the first signal comprises setting the frequency of the first signal generated by the local oscillator of the RF receiver circuitry, whereby a tone energy of an output of the RF receiver circuitry to an analogue to digital converter (ADC) on the received wireless network signal lies between the VLIF frequency and a frequency of zero.
15. The method of claim 8 , wherein:
the RF receiver circuitry is operating in a very low intermediate frequency (VLIF) mode during normal operations;
the VLIF is a positive frequency; and
the setting the first signal comprises adding an offset to one or more mixers of the RF receiver circuitry, whereby a tone energy of an output of the RF receiver circuitry to an ADC on the received wireless network signal lies between the VLIF frequency and a frequency of zero.
16. The method of claim 15 , wherein:
the received wireless network signal comprises an FCCh tone; and
the setting comprises setting the frequency of the signal generated by the local oscillator of the RF receiver circuitry whereby an FCCh tone energy of the output of the RF receiver circuitry to the ADC on the received FCCh tone lies between the VLIF frequency and a frequency of zero.
17. A wireless communication unit comprising an integrated circuit according to claim 1 , wherein:
in the DCR mode, the processing logic is arranged to determine the I/Q imbalance based on the in-phase and quadrature digital baseband representations of the received wireless network signal; and
in the I/F mode, the RF receiver circuitry is to transform received other wireless network signals to signals at an intermediate frequency, to transform the signals at the intermediate frequency to baseband, and to transform the baseband to audio for a user of the wireless communication unit.
18. The wireless communication unit of claim 17 , wherein the wireless communication device is one of a private mobile radio, a cellular phone, a personal digital assistant, a wireless capable laptop computer.
19. The wireless communication unit of claim 18 , wherein the cellular phone supports at least one of the following communication formats: Global System for Mobile communications (GSM), general packet radio system (GPRS), enhanced general packet radio system (EGPRS), and enhanced GSM (EGSM).