A balanced-to-unbalanced converter (balun) is provided, including: a converting circuit having a first processing circuit including a first inductor and a first capacitor connected in series, a second processing circuit including a second capacitor and a second inductor connected in series, the second capacitor being electrically connected to the first inductor, and two balanced output ends connected to the first processing circuit and the second processing circuit, respectively; and a preprocessing circuit connected to the converting circuit and including an unbalanced input end for converting real impedance at the unbalanced input end into complex impedance at the balanced output ends. Accordingly, the balun satisfies the need of the wireless communication chips by providing differential signals with complex impedance. This is done by employing the preprocessing circuit in conjunction with the converting circuit to convert an unbalanced signal with real impedance into a balanced signal with complex impedance.