Switchable directional coupler for use with RF devices
The embodiments of the present invention provide a directional coupler switchable between a normal state and a bypass state. In one embodiment, the directional coupler comprises shunt switches for switching between the normal state and the bypass state, and first and second transmission lines each extending between first and second ends, wherein the shunt switches comprises a first switch coupled to the first end of the first transmission line, a second switch coupled to the first end of the first transmission line, and a third switch coupled between the second end of the first transmission line and the second end of the second transmission line.
1. A radio frequency (RF) transceiver, comprising:
an RF transmitter;
an RF receiver; and
a directional coupler switchable between a normal state and a bypass state and coupled between an antenna and the RF transmitter and between the antenna and the RF receiver, the directional coupler in the normal state allowing passage of a large portion of a transmit signal from the RF transmitter to the antenna and coupling a portion of a received RF signal from the antenna to the RF receiver, the directional coupler in the bypass state directing the received RF signal from the antenna to the RF receiver with a single switch,
wherein the directional coupler comprises first and second transmission lines each extending between first and second ends, a first shunt switch coupled to the first end of the first transmission line, a second shunt switch coupled to the first end of the second transmission line, and a third shunt switch coupled between the second end of the first transmission line and the second end of the second transmission line.
2. The RF transceiver of claim 1 , wherein the directional coupler in the bypass state provides a short circuit at an input port coupled to the RF transmitter and functions as a quarter-wave transformer that isolates the received RF signal from the short circuit.
3. The RF transceiver of claim 1 , wherein each shunt switch comprises at least one PIN diode.
4. The RF transceiver of claim 3 , wherein the PIN diodes associated with the first and second switches have a common node that is DC biased with a resistor and RF bypassed to ground with a capacitor.
5. The RF transceiver of claim 1 , wherein each shunt switch comprises at least one field effect transistor.
6. The RF transceiver of claim 1 , further comprising a drive circuit to allow control of the shunt switches using a control signal, the drive circuit comprising a pair of inverters and providing a return current path through a common node of a pair of PIN diodes.
7. A radio frequency (RF) transceiver, comprising:
an RF transmitter;
an RF receiver; and
a directional coupler switchable between a normal state and a bypass state and coupled between an antenna and the RF transmitter and between the antenna and the RF receiver, the directional coupler in the normal state allowing passage of a large portion of a transmit signal from the RF transmitter to the antenna through a first transmission path and coupling a portion of a received RF signal from the antenna to the RF receiver through a second transmission path, the directional coupler in the bypass state directing the received RF signal from the antenna to the RF receiver with a single switch through a third transmission path and wherein the directional coupler functions as a quarter-wave transformer that isolates the received RF signal from an input port coupled to the RF transmitter, and wherein the first and second transmission paths of the directional coupler comprise:
first and second transmission lines each extending between first and second ends;
a first shunt switch coupled to the first end of the first transmission line;
a second shunt switch coupled to the first end of the second transmission line; and
a third shunt switch coupled between the second end of the first transmission line and the second end of the second transmission line.
8. The RF transceiver of claim 7 , wherein the directional coupler in the bypass state provides a short circuit at the input port coupled to the RF transmitter and functions as a quarter-wave transformer that isolates the received RF signal from the short circuit.
9. The RF transceiver of claim 7 , wherein each shunt switch comprises at least one PIN diode.
10. The RF transceiver of claim 9 , wherein the PIN diodes associated with the first and second switches have a common node that is DC biased with a resistor and RF bypassed to ground with a capacitor.
11. The RF transceiver of claim 7 , wherein each shunt switch comprises at least one field effect transistor.
12. The RF transceiver of claim 7 , further comprising a drive circuit to allow control of the shunt switches using a control signal, the drive circuit comprising a pair of inverters and providing a return current path through a common node of a pair of PIN diodes.