Systems and methods to switch radio frequency signals for greater isolation
In semiconductor switches, the isolation can be limited by the capacitive coupling between the switch input and the switch output. Ultra-high isolation can be achieved by adding a coupled transmission line to the semiconductor switch. The coupled transmission line introduces inductive coupling, which cancels at least a part of the capacitive coupling between the switch input and the switch output.
1. A portable transceiver comprising:
an antenna configured to receive a radio frequency input signal and to transmit a radio frequency output signal;
a transmitter configured to provide the antenna with the radio frequency output signal;
a receiver configured to amplify the received radio frequency input signal; and
a switching circuit including a coupled transmission line having a first transmission line and a second transmission line, and first and second transistors electrically connected in series, the switching circuit having a common terminal in communication with the antenna, a first terminal in communication with the receiver through the first transmission line, and a second terminal in communication with the transmitter through the second transmission line, the switching circuit configured to switch the radio frequency input signal from the antenna to the receiver through the first transmission line and to disconnect the antenna from the transmitter, the second transmission line inducing an inductive signal which cancels at least a portion of a capacitive signal generated by the radio frequency input signal capacitive coupling through the switching circuit to the transmitter.
2. The portable transceiver of claim 1 wherein the switching circuit includes an ultra-high isolation single pole double throw switch.
3. The portable transceiver of claim 1 wherein the switching circuit has a receive state and a transmit state.
4. The portable transceiver of claim 1 wherein the first and second transistors include field-effect transistors.
5. The portable transceiver of claim 1 wherein the first and second transistors include bipolar-junction transistors.
6. The portable transceiver of claim 1 wherein at least one of the first and second transistors include four transistor devices electrically connected in series.
7. The portable transceiver of claim 1 wherein the switching circuit further includes a third transistor in communication with the first terminal.
8. The portable transceiver of claim 7 wherein the switching circuit further includes a fourth transistor in communication with the second terminal.
9. A method to improve signal isolation in a portable transceiver, the method comprising:
receiving at a switching circuit a radio frequency input signal from an antenna, the switching circuit including a coupled transmission line having a first transmission line and a second transmission line, and first and second transistors electrically connected in series, the switching circuit having a common terminal in communication with the antenna, a first terminal in communication with a receiver through the first transmission line, and a second terminal in communication with a transmitter through the second transmission line; and
switching the switching circuit to conduct the radio frequency input signal from the antenna to the receiver through the first transmission line and to disconnect the antenna from the transmitter, a capacitive signal being generated by capacitive coupling of the radio frequency input signal through the switching circuit to the transmitter.
10. The method of claim 9 wherein an inductive signal is induced in the second transmission line.
11. The method of claim 10 wherein the inductive signal cancels at least a portion of the capacitive signal to provide isolation improvement.
12. The method of claim 9 wherein the switching circuit includes an ultra-high isolation single pole double throw switch.
13. The method of claim 9 wherein the switching circuit has a receive state and a transmit state.
14. The method of claim 9 wherein the first and second transistors include field-effect transistors.
15. The method of claim 9 wherein the first and second transistors include bipolar-junction transistors.
16. The method of claim 9 wherein at least one of the first and second transistors include four transistor devices electrically connected in series.
17. The method of claim 9 wherein the switching circuit further includes a third transistor in communication with the first terminal.
18. The method of claim 17 wherein the switching circuit further includes a fourth transistor in communication with the second terminal.
19. The method of claim 9 further comprising receiving a radio frequency output signal from the transmitter and switching the switching circuit to conduct the radio frequency output signal from the transmitter to the antenna through the second transmission line and to disconnect the antenna from the receiver.