| 摘要 |
A HOMODYNE RADIO RECEIVING APPARATUS IS PROVIDED FOR MITIGATING FIXED OR VARIABLE DC OFFSETS PRODUCED BY RESIDUAL SECOND ORDER INTERMODULATION TERMS DUE TO UNWANTED SIGNALS. THE HOMODYNE RADIO RECEIVING APPARATUS INCLUDES AN ANTENNA (1), AN ANTENNA BAND-PASS FILTER (2), AN RF AMPLIFIER (4) AND A QUADRATURE DOWNCONVERTER (5). THE QUADRATURE DOWNCONVERTER FOR THE COMPLEX BASE BAND IS CENTERED AROUND A DESIRED RECEPTION FREQUENCY SO THAT THE COMPLEX BASEBAND SIGNALS LIE AROUND ZERO FREQUENCY. A SUPPLEMENTARY TOTAL POWER DETECTOR (6) IS PROVIDED TO MEASURE THE TOTAL RECEIVED POWER THROUGH THE ANTENNA BAND-PASS FILTER (2) SO THAT THE UNWANTED TERMS CAUSED BY SECOND ORDER INTERMODULATION ARE COMPENSATED. THE COMPENSATION IS ACHIEVED BY FEEDING INSTANTANEOUS POWER MEASUREMENTS TO A SIGNAL PROCESSING UNIT (13;20) ALONG WITH THE COMPLEX BASEBAND SIGNALS. THE SIGNAL PROCESSING UNIT (13;20) THEN DETERMINES A COMPLEX COMPENSATION COEFFICIENT BY CORRELATING THE POWER SIGNAL WITH THE COMPLEX BASEBAND SIGNALS. THE COMPLEX COMPENSATION COEFFICIENT IS THEN EMPLOYED TO SUBTRACT A WEIGHTED AMOUNT OF THE POWER SIGNAL FROM THE COMPLEX BASEBAND SIGNALS IN ORDER TO CANCEL THE UNWANTED SECOND ORDER INTERMODULATION DISTORTION TERMS.
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