Patent ID: 7555273

Claim:
A bandpass filter comprising: a first transposition circuit coupled to receive an input signal, wherein the first transposition circuit is configured to perform first and second signal transpositions using first and second mixing signals, respectively, in order to produce a first transposed signal, wherein the first and second mixing signals are of different frequencies, wherein the first transposition circuit includes a first upstream mixer coupled to receive the input signal and the first mixing signal and configured to perform the first signal transposition, a first low-pass filter configured to perform low-pass filtering of an output signal received from the first upstream mixer, and a first downstream mixer coupled to receive the second mixing signal and an output signal from the first low-pass filter and configured to perform the second signal transposition; a second transposition circuit coupled to receive the input signal, wherein the second transposition circuit is configured to perform third and fourth signal transpositions using third and fourth mixing signals, respectively, in order to produce a second transposed signal, wherein the third and fourth mixing signals are of the same frequencies as the first and second mixing signals, respectively, wherein the second transposition circuit includes a second upstream mixer coupled to receive the input signal and the third mixing signal and configured to perform the third signal transposition, a second low-pass filter configured to perform low-pass filtering of an output signal received from the second upstream mixer, and a second downstream mixer coupled to receive the fourth mixing signal and an output signal from the second low-pass filter and configured to perform the fourth signal transposition; and an output unit coupled to receive the first and second transposed signals, wherein the output unit is configured to produce a filtered output signal by taking one of a sum or a difference of the first and second output signals; wherein the bandpass filter has an upper limit B for a frequency band in which filtering is performed, wherein the upper limit is defined by a relationship B>|{acute over (ω)} 0 −{acute over (ω)} 1 |, wherein {acute over (ω)} 0 is a frequency of the first and third mixing signals, and {acute over (ω)} 1 is a frequency of the second and fourth mixing signals.