Patent ID: 7672658

Claim:
A frequency-converting circuit, used for converting an radio frequency (RF) signal into a first baseband signal according to a poly-phase local oscillating (LO) signal; the frequency-converting circuit comprising: a coupler for receiving and splitting the RF signal and delivering a first RF signal via a first output terminal thereof, wherein the coupler further delivers a second RF signal via a second output terminal, the second RF signal and the first RF signal are quadrature to each other, and the coupler comprises: a first transformer having a primary winding and a secondary winding, wherein the first end of the primary winding is for receiving the RF signal, the second end of the primary winding is for producing the first RF signal and the first end of the secondary winding is for producing the second RF signal; a second capacitor, connected in series between the second end of the primary winding of the first transformer and the ground; a third capacitor, connected in series between the second end of the primary winding of the first transformer and the first end of the secondary winding of the first transformer; a third resistor, connected in series between the second end of the secondary winding of the first transformer and the ground; a fourth capacitor, connected in series between the second end of the secondary winding of the first transformer and the ground; a fifth capacitor, connected in series between the first end of the primary winding of the first transformer and the ground; a sixth capacitor, connected in series between the first end of the primary winding of the first transformer and the second end of the secondary winding of the first transformer, and a seventh capacitor, connected in series between the first end of the secondary winding of the first transformer and the ground; a first transduction unit, electrically connected to the first output terminal and used for amplifying the first RF signal; and a first switching unit, electrically connected to the first transduction unit and used for performing switching operations on the output signal of the first transduction unit according to the poly-phase LO signal and producing the first baseband signal.