A signal converter. The signal converter converts an analog inphase signal and an analog quadrature phase signal into a digital baseband inphase signal and a digital baseband quadrature phase signal. The analog inphase signal and the analog quadrature phase signal are orthogonal to each other and are carried in a predetermined intermediate frequency. The digital baseband inphase signal and the digital baseband quadrature phase signal are carried in zero frequency. The signal converter comprises a signal combiner combining the analog inphase signal and the analog quadrature phase signal to obtain an analog combined signal, an analog to digital converter converting the analog combined signal to a digital combined signal, and a signal separator separating the digital combined signal to obtain the digital baseband inphase signal and the digital baseband quadrature phase signal.