US Patent 7129803 Tuned transformer balun circuit and applications thereof

A tuned transformer balun circuit includes a transformer balun, a first tuning capacitor, a second tuning capacitor, and a third tuning capacitor. A first plate of the first tuning capacitor is operably coupled to a first node of the differential winding and a second plate of the first tuning capacitor is operably coupled to a circuit ground. A first plate of the tuning capacitor is operably coupled to a second node of the differential winding and a second plate of the second tuning capacitor is operably coupled to the circuit ground. A first plate of the third tuning capacitor is operably coupled to a first node of the single-end winding and the second plate of the third tuning capacitor is operably coupled to transceiver radio frequency signals, wherein, based on loading of the single-ended winding and the differential winding, the first, second, and third tuning capacitors resonate with the transformer balun to provide efficient energy transfer from the transmitter section to the antenna.