Impedance matched passive radio frequency transmit/receive switch
View Patent ↗A Radio Frequency (RF) structure services an antenna having a characteristic impedance and includes a differential Power Amplifier (PA), a differential Low Noise Amplifier (LNA), and a balun transformer. The differential PA has a differential PA output with a PA differential output impedance. The differential LNA has a differential LNA input with an LNA differential input impedance. The balun transformer has 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, and a turns ratio of the single ended winding and the differential winding. The turns ratio and the first pair of tap connections impedance match the PA differential output impedance to the characteristic impedance of the antenna. The turns ratio and the second pair of tap connections impedance match the LNA differential input impedance to the characteristic impedance of the antenna.
1. A balun transformer for servicing an antenna having a characteristic impedance, a differential Power Amplifier (PA) having a differential PA output impedance, and a differential Low Noise Amplifier (LNA) having a differential LNA input impedance, the balun transformer comprising:
a singled ended winding having an antenna connection; and
a differential winding having:
a pair of PA tap connections; and
a pair of LNA tap connections; and
a turns ratio of the single ended winding and the differential winding, wherein:
the turns ratio and the pair of PA tap connections impedance match the differential PA output impedance to the characteristic impedance of the antenna; and
the turns ratio and the pair of LNA tap connections impedance match the differential LNA input impedance to the characteristic impedance of the antenna.
2. The balun transformer of claim 1 , wherein:
the pair of PA tap connections has a first effective turns ratio with the single ended winding;
the pair of LNA tap connections have a second effective turns ratio with the single ended winding; and
the first effective turns ratio differs from the second effective turns ratio.
3. The balun transformer of claim 2 , wherein the differential PA output impedance is less than the differential LNA input impedance.
4. The balun transformer of claim 1 , wherein the LNA comprises a common-gate topology construction.
5. The balun transformer of claim 1 , wherein the LNA comprises a cross-coupled topology construction.
6. The balun transformer of claim 1 , wherein the single ended winding comprises:
an antenna tap connection; and
a ground tap connection.
7. The balun transformer of claim 1 , wherein:
the differential PA output impedance is a turned-on impedance; and
the differential LNA output impedance is a turned-on impedance.
8. The balun transformer of claim 1 , wherein:
the differential PA output impedance is greater than a turned-off PA differential output impedance of the PA; and
the differential LNA output impedance is greater than a turned-off LNA differential output impedance of the PA.