A signal receiving apparatus includes: a first amplifying device, a second amplifying device, a feedback device, and a mixing device, wherein the mixing device is a passive mixer, the second amplifying device is arranged to provide an input impedance looking into an input terminal of the second amplifying device to fall within a first impedance range when the second amplifying device operates in a first frequency range, the second amplifying device is arranged to provide the input impedance looking into the input terminal of the second amplifying device to fall within a second impedance range when the second amplifying device operates in a second frequency range, the second frequency range is different from the first frequency range, and the second impedance range is different from the first impedance range.