Patent ID: 7558543

Claim:
A radio frequency tuner comprising: a frequency converter arrangement comprising a first quadrature frequency converter having first and second mixers for providing in-phase and quadrature signals, electronically adjustable in-phase and quadrature filters for filtering said in-phase and quadrature signals, respectively, and a second quadrature frequency converter having third and fourth mixers for receiving said filtered in-phase and quadrature signals, respectively; a signal generator for generating a test tone of an adjustable frequency; an amplitude measuring stage for measuring a signal amplitude downstream of said third and fourth mixers; a differential phase measuring stage for measuring a phase difference between signals downstream of said third and fourth mixers; and a controller arranged, during a first alignment phase, to cause said signal generator to supply one at a time a plurality of tones of different frequencies to said frequency converter arrangement, to record amplitudes measured by said measuring stage for said tones, and to adjust a first of said quadrature filters based on said recorded amplitudes so as to provide a predetermined frequency response, said controller being arranged, during a second alignment phase, to perform the steps of: (a) causing said signal generator to supply one at a time first and second tones of different frequencies to said frequency converter; (b) forming a difference between phase differences measured by said differential phase measuring stage for said first and second tones; (c) adjusting a second of said quadrature filters; and (d) repeating said steps (a) to (c) until said difference formed in said step (b) meets a predetermined criterion.