Patent ID: 7079823

Claim:
A bandpass filtering method for a bandpass filter comprising: performing two frequency transpositions in parallel on an input signal (SE) for filtering using respective first and second upstream mixing signals (SM 1 , SM 2 ) that are substantially in phase quadrature so as to obtain respective first and second transposed signals (ST 1 , ST 2 ), filtering the two transposed signals respectively by two lowpass filters (F 1 , F 2 ), the frequency (ω 0 ) of the transposed signals and a passband (B/2) of the low-pass filters being related to the frequency (ω e ) of the input signal (SE) and to a passband desired for the bandpass filter, performing respective frequency transpositions on first and second filtered transposed signals (STF 1 , STF 2 ) using two respective downstream mixing signals (SMV 1 , SMV 2 ), taking a sum or a difference of the first and second filtered transposed signals (STF 1 , STF 2 ), selecting the frequency of the downstream mixing signals (SMV 1 , SMV 2 ) to be different from the frequency of the first and second upstream mixing signals so that an output signal is transposed into a desired frequency range, wherein a common oscillator (LO) is used which is coupled with a first phase shifter (MTM) to produce the upstream mixing signals and which is coupled with a second phase shifter (MTV) to produce the downstream mixing signals, and the phase shifters are used in opposite manner on first and second signal branches (VT 1 , VT 2 ) so that each of said first and second signal branches (VT 1 , VT 2 ) receives a phase-advanced output signal from one of the two phase shifters and a phase-delayed output signal from the other of the two phase shifters.