Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
  • H04B1/06—Receivers
  • H04B1/10—Means associated with receiver for limiting or suppressing noise or interference
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03D—DEMODULATION OR TRANSFERENCE OF MODULATION FROM ONE CARRIER TO ANOTHER
  • H03D3/00—Demodulation of angle-, frequency- or phase- modulated oscillations
  • H03D3/007—Demodulation of angle-, frequency- or phase- modulated oscillations by converting the oscillations into two quadrature related signals
  • H03D3/009—Compensating quadrature phase or amplitude imbalances
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L27/00—Modulated-carrier systems
  • H04L27/0014—Carrier regulation
  • H04L2027/0016—Stabilisation of local oscillators
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L27/00—Modulated-carrier systems
  • H04L27/0014—Carrier regulation
  • H04L2027/0024—Carrier regulation at the receiver end

Definitions

• the present invention relates to calibration of a quadrature receiver.
• a quadrature receiver operates in the so-called 2.4 GHz ISM band, for instance, or can be any other suitable receiver.
• US Patent No. 5,949,821 discloses a radio communication device that demodulates a signal using in-phase and quadrature components.
• the radio communication device has an equalizer for correcting phase and gain imbalances that would otherwise distort a received signal.
• the equalizer determines peak amplitudes for the in-phase and quadrature components of the received signal.
• the phase imbalance between the in-phase and quadrature components is determined using the peak amplitudes.
• the peak amplitudes and phase imbalance are used to adjust at least one of the in-phase and quadrature components to correct for any imbalance therebetween.
• a phase estimator estimates the phase imbalance between the in-phase and quadrature components that were separated from a sampled down- converted received signal by a pair of quadrature mixers by mixing with respective sin( ⁇ t) and cos( ⁇ t) signals.
• the phase imbalance is determined as the arcsin function of the product of two over the product of peak amplitude estimates of the uncorrected in-phase and quadrature components and the cross-correlation between the uncorrected in-phase and quadrature components.
• the equalizer thus corrects amplitude and phase imbalances of a received signal, i.e. a useful signal.
• phase adjustment is independent of gain errors in in-phase and quadrature branches of the receiver. It is another object of the invention to provide a quadrature receiver wherein such phase adjustment uses a phase adjustment signal obtained from cross-correlated quadrature output signals of the receiver.
• a method of calibrating a receiver comprising: ensuring that an input of said receiver receives no useful signals; cross-correlating quadrature output signals provided by said receiver, said quadrature output signals representing noise signals; and adjusting a relative phase of quadrature local oscillator signals that are used to generate said quadrature output signals through down-conversion of a received signal, said adjusted relative phase being obtained from said cross-correlated quadrature output signals.
• the invention is based on the insight of generating balanced quadrature signals at an early point in the receiver, i.e. at down-conversion of the received signal so that no further complicated corrections are needed, and further on the insight that cross-correlation of low pass filtered noise signals provides a signal that represents a phase imbalance that is independent of gain errors in the in-phase and quadrature branches of the receiver.
• the receiver is a zero-IF receiver.
• the relative phase of the quadrature local oscillator is set at a minimum cross-correlation value.
• DC-offsets in the in-phase and quadrature branches are removed by AC-couplers.
• the receiver is a low-IF receiver.
• the relative phase of the quadrature local oscillator is set at a zero cross-correlation value.
• an input of the receiver may be decoupled from an antenna that receives useful signals.
• cross-correlation is purely based on noise signals.
• Fig. 1 is a block diagram of a transceiver with a receiver according to the present invention.
• Fig. 2 is a circuit diagram showing an embodiment of phase adjustment of a local oscillator according to the present invention.
• Fig. 3 shows cross-correlation of low pass filtered signals according to the present invention.
• Fig. 4 illustrates cross-correlation in a zero-IF receiver according to the present invention.
• Fig. 5 is a flow-chart illustrates phase adjustment according to the invention.
• Fig. 1 is a block diagram of a transceiver 1 according to the present invention.
• the transceiver 1 operates in the so-called 2.4 GHz ISM (Industrial, Scientific and Medical) band, and is a so-called zero-IF transceiver that receives and transmits at the same frequency so that only a single tuned oscillator is needed.
• the transceiver 1 can be a so-called zero-IF (Intermediate Frequency) or low-IF transceiver.
• the transceiver 1 comprises a receive branch 2 and a transmit branch 3.
• the invention may also be embodied in a receiver. In that case no transmit branch is present.
• the receive branch 2 comprises a low noise amplifier (LNA) 4 that is coupled to an antenna 5 via a filter 6 and a transmit/receive switch 7.
• the LNA 4 is coupled to a pair of quadrature mixers 8 and 9 in respective in-phase and quadrature receive branches.
• the mixer 8 is coupled to a low pass filter 11.
• the low pass filter 11 is coupled to an analog-to-digital converter 13.
• the mixer 9 is coupled to an AC-coupler 15.
• the AC-coupler 15 is coupled to an analog-to- digital converter 16.
• the AC-couplers 12 and 15 may be provided in case of a zero-IF transceiver in order to remove DC-offset errors in the receive branch 2.
• the analog-to-digital converters 13 and 16 are part of base band processing means 17 and provide samples of quadrature signals V ⁇ (t) and V Q (I) that are obtained by down-converting a received radio frequency signal.
• the quadrature signals V ⁇ (t) and VQ(t) may be zero-IF or low-IF signals.
• the base band processing means 17 further comprises a processor 18, a non- volatile memory 19 storing program data and other non-volatile data, a volatile memory 20 for storing volatile data, and a digital-to-analog converter 21 for providing a phase adjustment signal 22 to adjust the relative phase of a pair of quadrature local oscillator signals 23 and 24 provided by local oscillator means 25 comprised in the receive branch 2.
• the phase adjustment signal 22 is determined from a noise signal v n (t) at an output of the low noise amplifier 4. It is assumed that a large part of the noise originates before the mixers, i.e. in the LNA 4.
• cross correlation and thereafter integration provides a signal V OUT that is represents the phase imbalance.
• V OUT represents the phase imbalance.
• the relative phase of the local oscillator is adjusted until cross-correlation provides a substantially zero output signal.
• the relative phase of the local oscillator is adjusted until cross-correlation provides a minimum output signal.
• V Q (t) LPF[v n (t). ⁇ .sin( ⁇ c t+ ⁇ )], ⁇ being the gain imbalance and ⁇ being the phase error.
• V Q (I) LPF[ ⁇ n ! (t).cos( ⁇ c t) - n Q (t).sin( ⁇ c t) ⁇ . ⁇ .sin( ⁇ c t+ ⁇ )]
• V Q (I) - ⁇ .cos( ⁇ ).n Q (t) + ⁇ .sin( ⁇ ).n ⁇ (t)
• v ⁇ (t) m(t)
• the relative phase of the quadrature local oscillator is set at a minimum cross-correlation value, thereby minimizing the quadrature phase imbalance.
• Fig. 2 is a circuit diagram showing an embodiment of phase adjustment of the local oscillator means 25 according to the present invention.
• the local oscillator means 25 comprises a local oscillator 30 which can be a VCO (Voltage Controlled Oscillator) controlled by a PLL (Phase Locked Loop) to which a stable reference oscillator signal is provided. Via an RC-circuit of a resistor 31 and a capacitor 32 first quadrature LO-signal is obtained, and via an RC-circuit of a capacitor 33 and a controlled field effect transistor 34 a second quadrature LO-signal is obtained, when balanced the first and second quadrature LO- signals exhibiting relative phase of 90°.
• VCO Voltage Controlled Oscillator
• PLL Phase Locked Loop
• the DAC 21 provides the phase adjustment signal 22 to the field effect transistor 34, the phase adjustment signal 22 being proportional to the phase error.
• Fig. 3 shows cross-correlation of low pass filtered signals according to the present invention.
• the low pass filtered quadrature signals v ⁇ (t) and V Q (I) are provided to inputs of a mixer 40 that is coupled to an integrator 41.

Landscapes

• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Superheterodyne Receivers (AREA)
• Circuits Of Receivers In General (AREA)

Priority Applications (3)

Applications Claiming Priority (2)

Publications (2)

Family

ID=24680626

Family Applications (1)

Country Status (6)

Cited By (1)

Families Citing this family (25)

Family Cites Families (8)

• 2000
  • 2000-09-21 US US09/668,014 patent/US6744829B1/en not_active Expired - Fee Related
• 2001
  • 2001-09-06 JP JP2002528904A patent/JP2004509547A/ja active Pending
  • 2001-09-06 EP EP01969701A patent/EP1325552A2/en not_active Withdrawn
  • 2001-09-06 WO PCT/EP2001/010320 patent/WO2002025804A2/en not_active Ceased
  • 2001-09-06 CN CN01802814A patent/CN1446397A/zh active Pending
  • 2001-09-06 KR KR1020027006430A patent/KR20020072540A/ko not_active Withdrawn

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