Impedance matched passive radio frequency transmit/receive switch

A Radio Frequency (RF) apparatus for servicing an antenna having a characteristic impedance, the RF apparatus comprising:

• a differential Power Amplifier (PA) having a differential PA output with a PA differential output impedance;
• a differential Low Noise Amplifier (LNA) having a differential LNA input with an LNA differential input impedance;
• and
• a balun transformer comprising:
• a singled ended winding coupled to the antenna;
• a differential winding having a first pair of tap connections coupled to the differential PA output and a second pair of tap connections coupled to the differential LNA input;
• a turns ratio of the single ended winding and the differential winding, wherein:
• the turns ratio and the first pair of tap connections impedance match the PA differential output impedance to the characteristic impedance of the antenna;
• and
• the turns ratio and the second pair of tap connections impedance match the LNA differential input impedance to the characteristic impedance of the antenna.

A method for designing a Radio Frequency (RF) structure, having a differential Power Amplifier (PA) with a PA differential output impedance, a differential Low Noise Amplifier (LNA) with a LNA differential input impedance, a balun transformer having a single ended winding and a differential winding, and an antenna having a characteristic impedance, the method comprising:

• in a first operation, selecting a topology and structure of the differential PA amplifier;
• and
• in a second operation, determining a turns ratio of the single ended winding and the differential winding and a first pair of tap connections of the balun transformer to impedance match the PA differential output impedance of the differential PA to the characteristic impedance of the antenna;
• in a third operation, selecting a topology and structure of the differential LNA amplifier to cause the LNA differential input impedance to roughly impedance match the characteristic impedance of the antenna when transformed by the turns ratio of the single ended winding and the differential winding;
• and
• in a fourth operation, determining a second pair of tap connections of the differential winding of the balun transformer to impedance match the LNA differential input impedance the characteristic impedance of the antenna.

A Radio Frequency (RF) apparatus comprising:

• a case;
• an antenna at least partially contained by the case and having a characteristic impedance;
• RF circuitry at least partially contained by the case, coupled to the antenna and comprising:
• a baseband processor;
• and
• an RF front end coupled to the baseband processor and comprising:
• a differential Power Amplifier (PA) having a differential PA output with a PA differential output impedance;
• a differential Low Noise Amplifier (LNA) having a differential LNA input with an LNA differential input impedance;
• and
• a balun transformer comprising:
• a singled ended winding coupled to the antenna;
• a differential winding having a first pair of tap connections coupled to the differential PA output and a second pair of tap connections coupled to the differential LNA input;
• a turns ratio of the single ended winding and the differential winding, wherein:
• the turns ratio and the first pair of tap connections impedance match the PA differential output impedance to the characteristic impedance of the antenna;
• and
• the turns ratio and the second pair of tap connections impedance match the LNA differential input impedance to the characteristic impedance of the antenna.