Switchable directional coupler for use with RF devices

• US 20070008132A1
• Filed: 07/11/2005
• Published: 01/11/2007
• Est. Priority Date: 12/23/2004
• Status: Active Grant

• Current Assignee: TriQuint Semiconductor Incorporated (Qorvo, Inc.)
• Original Assignee: TriQuint Semiconductor Incorporated (Qorvo, Inc.)
• Inventors: Bellantoni, John
• Granted Patent: US 7,546,089 B2
• Time in Patent Office: Days
• US Class Current: 340/572.100
• CPC Class Codes: H01P 5/04 with variable factor of coupling

Abstract

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.

Claims

1. A directional coupler switchable between a normal state and a bypass state and comprising first, second, and third ports, wherein the directional coupler in the normal, state allows a large portion of a first signal received at the first port to pass to the second port and couples a portion of a second signal received at the second port to the third port, and wherein the directional coupler in the bypass state provides a direct path for the second signal received at the second port to pass to the third port.

2. The directional coupler of claim 1, wherein the directional coupler in the bypass state provides a short circuit at the first port and functions as a quarter-wave transformer that isolates the second signal from the short circuit.

3. The directional coupler of claim 1, further comprising shunt switches for switching between the normal state and the bypass state

4. The directional coupler of claim 3, further comprising 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 second 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.

5. The directional coupler of claim 3, wherein each shunt switch comprises at least one PIN diode.

6. The directional coupler of claim 5, 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.

7. The directional coupler of claim 3 wherein each shunt switch comprises at least one field effect transistor.

8. The directional coupler of claim 3, further comprising a drive circuit to allow control of the shunt switches using a single control signal.

9. The directional coupler of claim 8, further comprising first and second transmission lines, wherein the control circuit applies DC bias to the switches through the transmission lines.

10. The directional coupler of claim 9, wherein the shunt switches comprise two pairs of PIN diodes, each pair of PIN diodes having a common node, and wherein the control circuit further comprises a pair of inverters for biasing the PIN diodes and provides a return current path through the common node of each pair of PIN diodes, whereby a full supply voltage from the control signal is applied across each PIN diode in the normal state of the directional coupler and bias current flows in the drive circuit in the bypass state of the directional coupler.

11. The directional coupler of claim 11, wherein the drive circuit further comprises a pair of inductors for isolating parts of the drive circuit from RF signals in the transmission lines.

12. 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.

13. The RF transceiver of claim 12, 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.

14. The RF transceiver of claim 12, 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.

15. The RF transceiver of claim 14, wherein each shunt switch comprises at least one PIN diode.

16. The RF transceiver of claim 15, 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.

17. The RF transceiver of claim 14, wherein each shunt switch comprises at least one field effect transistor.

18. The RF transceiver of claim 14, 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.

19. A method of operating a radio frequency identification (RFID) interrogator having a radio frequency (RF) receiver coupled to an antenna through a switchable directional coupler, comprising:

setting a logic input to a control terminal of the directional coupler to a first level to allow the directional coupler to operate in a bypass state and the RFID interrogate to operate in a LISTEN mode, whereby the antenna is connected to the RF receiver through a single switch; and

setting the logic input to a second level to allow the directional coupler to operate in a normal state and the RFID interrogator to transmit RF signals for interrogating at least one RFID tag, the RF signals encountering a single OFF state shunt switch when traversing the directional coupler.

20. The method of claim 19, further comprising receiving a backscattered signal from the at least one RFID tag when the directional coupler operates in the normal state, the backscattered signal encountering a single OFF state shunt switch when traversing the directional coupler.