WO2009095815A2

WO2009095815A2 - Antenna interface circuit and method for transmitting and receiving signals in collocated wireless communication systems

Info

Publication number: WO2009095815A2
Application number: PCT/IB2009/050212
Authority: WO
Inventors: Artur Wrzyszcz
Original assignee: Nxp B.V.
Priority date: 2008-01-31
Filing date: 2009-01-21
Publication date: 2009-08-06
Also published as: WO2009095815A3

Abstract

The invention relates to an antenna interface circuit and a method for transmitting and receiving signals in collocated wireless communication systems. The collocated wireless communication systems operate at least partially in the same frequency band. The Problem to be solved is to improve the performance of shared antenna systems compared to separate antenna systems and to support antenna diversity with the same interface circuit. The current invention substantially solves the problems of both the splitter- based shared antenna solution (high insertion loss) and the switch-based antenna solution (limited support of simultaneous operation). The antenna interface circuit in the present invention solves the problem by means of a directional coupler with four coupler ports where the first coupler port is attached to the first antenna port of the mobile device and with the thirdfourth coupler port to the second antenna port of the mobile device and a DPDT switch (DPDT = double pole double throw) with four switch ports, four switches and two control lines is attached with a first switch port to the second coupler port and with the second switch port to the third coupler port and antenna is connected with the third switch port.

Description

DESCRIPTION

ANTENNA INTERFACE CIRCUIT AND METHOD FOR TRANSMITTING AND RECEIVING SIGNALS IN COLLOCATED WIRELESS COMMUNICATION SYSTEMS

The invention relates to an antenna interface circuit for transmitting and receiving signals in collocated wireless communication systems. The communication systems are integrated in a mobile device with a first wireless communication system provided with a first antenna device port and a second wireless communication system provided with a second antenna device port. The collocated wireless communication systems operate at least partially in the same frequency band.

The invention relates also to a method for transmitting and receiving signals in collocated wireless communication systems where in a mobile device a first part receives and transmits signals in a first wireless communication system via a first antenna device port and a second part receives and transmits signals in a second wireless communication system via a second antenna device port. The collocated wireless communication systems operate at least partially in the same frequency band.

Collocated wireless communication systems, e.g. Bluetooth (BT) and

Wireless LAN (WLAN) systems, are often integrated in mobile devices like cellular phones, i.e. the devices are divided in two parts, the first part related to a first wireless communication system and the second part related to a second wireless communication system.

Collocated systems may operate in the same or overlapping frequency bands.

For example, BT and WLAN operate in the same 2.4 GHz unlicensed frequency band. . BT and WLAN systems are often integrated in mobile devices like cellular phones. In many use case scenarios, BT and WLAN systems can operate simultaneously. In such applications, the following collision types are possible: a) Both parts of the device are transmitting in-band: One or both of the data packets of the first or the second wireless communication might be received with errors.

b) Both parts of the device are receiving in-band: One or both of the data packets might be received with errors.

c) The first part is transmitting and the second part is receiving: The locally received data packet is received with errors.

Table 1 and

Table 2 show possible collision cases exemplified with collocated BT and WLAN systems.

Table 1 : Collision cases as a function of local activities

Table 2: Definition of collision types

As explained in 802.15.2 -,TM , IEEE Recommended Practice for Information technology - Telecommunications and information exchange between systems - Local and metropolitan area networks - Specific requirements, Part 15.2: Coexistence of Wireless Personal Area Networks with Other Wireless Devices Operating in Unlicensed Frequency Bands, Aug. 2003, these collisions can be to some extent avoided by using BT-WLAN coexistence mechanisms. For example, packet traffic arbitration (PTA) can be implemented for controlling transmission access to the medium.

Fig. 1 to Fig. 4 show several possible antenna configurations for WLAN and

BT systems. As shown in Fig. 1 and Fig. 2 typically, each system has its own antenna. As depicted in Fig. 2 some WLAN systems use two antennas for antenna diversity implementation. In mobile devices, the antenna isolation usually does not exceed 20 dB. For cost and size reasons, it is desirable to share the antenna between the BT and WLAN systems as shown in Fig. 2 and 3. Simple ways of single BT-WLAN antenna implementation include either a signal splitter/combiner as shown in Fig. 3 or an antenna switch as shown in Fig. 4. The splitter solution as shown in Fig. 3 allows simultaneous access to the medium but it adds a significant insertion loss (c.a. 3.5 dB) in both WLAN and BT signal paths reducing the transmitter output power and receiver sensitivity. The insertion loss is present even when either WLAN or BT system is powered off.

The antenna switch solution shown in Fig. 4 does not permit simultaneous access to the medium and it relies on the BT-WLAN coexistence protocol to control the switch. However, this solution adds only relatively small insertion loss to the BT and WLAN signal paths.

The problem to be solved by the present invention is to improve the performance of shared antenna systems compared to separate antenna systems and to support antenna diversity using the same interface circuitry. The present invention substantially solves the problems of both the splitter-based shared antenna solution (high insertion loss) and the switch-based antenna solution (limited support of simultaneous operation).

The antenna systeminterface circuit in the present invention solves the problem by means of a directional coupler with four coupler ports where the first coupler port is attached to the first antenna port of the mobile device and with the third coupler port to the second antenna port of the mobile device and a DPDT switch (DPDT = double pole double throw) with four switch ports, four switches and two control lines is attached with the first switch port to the second coupler port and with the second switch port to the third coupler port and antenna is connected to the third switch port.

The arrangement of a directional coupler and a DPDT antenna switch facilitates with the same structure both single shared antenna and shared antenna diversity applications for the first and the second wireless communication systems. Thereby the invention enables: • Simultaneous access to the medium for both wireless communication systems. At any given moment of time, one of the systems has priority access to the medium with low insertion loss. The other system can operate concurrently but with significantly higher insertion loss. Arbitration of the priority access to the medium should be based on a coexistence protocol for both systems, e.g. the BT-WLAN coexistence protocol, in order to optimise the system performance. The underlying algorithms are not subject of this invention.

• High isolation between the both ports of the both parts comparable with the antenna isolation between separate antennas for the different antennas located on the same mobile device (e.g. cellular phone).

• Low insertion loss if only one of the two systems is enabled.

In an embodiment of the invention, the third switch port is connected to the antenna and the fourth switch port is terminated by an RF matching element. Therein the fourth switch port may be terminated by a resistor interposed between the fourth switch port and ground.

In a further embodiment of the invention, the fourth switch port may be connected to an input of a power detection device. This arrangement is suitable for an accurate output power measurement of the first and the second wireless communication pathsystem under antenna impedance mismatch conditions.

The positions of the directional coupler and the DPDT switch can be swapped yielding an equivalent circuit. The DPDT antenna switch is used to control the operation mode of the system as described in the inventive method description.

In a further embodiment of the invention, the third switch port is connected to the antenna and the fourth switch port is connected to a second antenna. In this case, the same antenna interface circuit is applicable to both a single shared antenna solution as well as a shared antenna diversity solutions for the first and the second wireless communication systems. HenceThis is advantageous, since a single SiP product (SiP = System in Package) implementing this structure can be applicable to both single and dual shared antenna systemssolutions.

In a further embodiment, the first part of the device is operating in a wireless LAN (WLAN) system and the second part is operating in a Bluetooth (BT) system.

The problems described above isare also addressed?????substantially solved by a method, characterized in the following steps:

- providing the mobile device with a directional coupler with four coupler ports;

- attaching the first coupler port to the first antenna port of the mobile device;

- attaching the third coupler port to the second antenna port of the mobile device;

- providing the mobile device with a DPDT switch with four switch ports, four switches and two control lines;

- attaching a first switch port to the second coupler port attaching the second switch port to the third coupler port;

- connecting the antenna with the third switch port;

- controlling the switch depending on the intended receiving or transmitting status of the first and the second part.

A first embodiment of the method is characterized in

- providing the DPDT switch with

. a first switch interposed between the first and the third switch port;

. a second switch interposed between the second and the fourth switch port; . a third switch interposed between the first and the second switch port;

. a fourth switch interposed between the second and the third switch port;

- attaching the third switch port to the antenna;

- terminating the fourth switch port with an RF matching element;

- controlling the switch depending on the intended receiving or transmitting status of the first and the second part as follows

An optional power detector interface enables accurate power measurement of the output power of both parts of the device under antenna impedance mismatch conditions. Therefore the inventions provides an embodiment of the Method which is characterized in

- providing the DPDT switch with

a first switch interposed between the first and the third switch port;

a second switch interposed between the second and the fourth switch port;

a third switch interposed between the first and the second switch port;

. a fourth switch interposed between the second and the third switch port;

- attaching the third switch port to the antenna; - terminating the fourth switch port with an RF matching element;

- connecting the fourth switch port to a power detection device measuring the output power in several measurement modes,

- controlling the switch depending on the intended receiving or transmitting status of the first and the second part and depending on the intended measurement mode as follows

Assuming that during the transmission power measurement only the first or the second system is active, this circuit allows the following measurements to be conducted:

- Measurement of the output power delivered to a load for both, first and second system;

- Measurement of the output power delivered by the first or the second power amplifier of the respective part of the device with the antenna load. In case of the antenna impedance mismatch, this measurement is not distorted by the reflected power, since the reflected power is absorbed by the impedances of the fist and second antenna ports.

A further embodiment of the Method is characterized in

- providing the DPDT switch with

. a first switch interposed between the first and the third switch port;

a second switch interposed between the second and the fourth switch port;

a third switch interposed between the first and the second switch port;

a fourth switch interposed between the second and the third switch port;

- attaching the third switch port to the antenna;

- connecting a second antenna with the fourth switch port;

With the help of this embodiment, the same circuit is applicable to a single shared antenna solution as well as a shared antenna diversity solutions for the first and the second wireless communication systems. HenceThis is advantageous, since a single SiP product implementing this structure can be applicable to both single and dual shared antenna implementations for both wireless communication systems.

In the following part, the invention is described in more detail by an application to a WLAN-system as the first system and a BT-system as the second system both implemented in the same device. Here three different embodiments are shown, a single

BT-WLAN antenna solution, a single BT-WLAN antenna solution with power detector and a shared BT-WLAN antenna diversity solution.

Fig. 1 a known antenna configuration for WLAN and BT systems with two antennas, one WLAN antenna and one BT antenna;

Fig. 2 a known antenna configuration for WLAN and BT systems with three antennas, two WLAN antennas and one BT antenna;

Fig. 3 a known antenna configuration for WLAN and BT systems with onea single shared antenna using a splitter;

Fig. 4 a known antenna configuration for WLAN and BT systems with onea single shared antenna using a switch;

Fig. 5 an inventive antenna systeminterface circuit with a single shared BT- WLAN antenna;

Fig. 6 an inventive antenna systeminterface circuit with a single shared BT- WLAN antenna solution with power detector and

Fig. 7 an inventive antenna systeminterface circuit with a shared BT-WLAN diversity solution.

All three embodiments show in Figs. 5 to 7 an antenna systeminterface circuit for transmitting and receiving signals in collocated wireless communication systems. The communication systems are integrated in a mobile device with a WLAN-communication system provided with a first antenna device port (1) and a BT-communication system provided with a second antenna device port (2). The collocated wireless communication systems operate in the same 2.4 GHz unlicensed frequency band. As shown in Fig. 5, a directional coupler (3) with four coupler ports Cl to C4 where the first coupler port Cl (input) is attached to the first antenna port (1) of the mobile device (not shown) and with the thirdfourth coupler port C34 (isolated) to the second antenna port (2) of the mobile device and a DPDT switch (4) with four switch ports S 1 to S4, four switches SWl to SW4 and two control lines A; B is attached with its first switch port S 1 to the second coupler port C2 (direct) and with the second switch port S2 to the third coupler port C3 (coupled) and an antenna (5) is connected with the third switch port CS3.

In the embodiment shown in Fig. 5, the third switch port S3 is connected to the antenna and the fourth switch port S4 is terminated by an RF matching resistor (6) interposed between the fourth switch port S4 and ground.

The DPDT antenna switch is used to control the operation mode of the system as described in Table 3. BT/WLAN insertion loss and BT-WLAN isolation values in Table 3 are given as guidance only.

Table 3 : Single BT-WLAN antenna operation modes

In a second embodiment of the invention shown in Fig. 6, the fourth switch port S4 is connected to the 50Ω load (6) and to the input of a power detection device (7). This arrangement is suitable for an accurate output power measurement of the first and the second communication pathsystem (1); (2) under antenna impedance mismatch conditions.

Assuming that during the TX power measurement only the WLAN or BT system is active, this circuit allows the following measurements to be conducted:

• Measurement of the output power delivered to a 50Ω load for both BT and WLAN.

• Measurement of the output power delivered by the WLAN or BT power amplifier with the antenna load. In case of the antenna impedance mismatch, this measurement is not distorted by the reflected power, since the reflected power is absorbed by the impedances of the BT and WLAN ports.

The output power measurement modes are summarized in Table 4.

Table 4: BT/WLAN output power measurement modes

In a third embodiment of the invention shown in Fig. 7, the third switch port S3 is connected to the antenna (5) and the fourth switch port S4 is connected to a second antenna (8). In this case, the same circuit is applicable to both single shared antenna as well as shared antenna diversity solutions for the WLAN and the BT-system. Here two antennas (5); (8) are connected to the DPDT 4 switch (4).

Whenever only the BT or WLAN system is active, it has full access to both antennas (5); (8) facilitating the antenna diversity implementation. In case both BT and WLAN systems are active, each can use a dedicated antenna (5) or (8) for optimum performance. The operation modes of the shared BT-WLAN antenna solution are described in Table 5.

Table 5 : Shared BT-WLAN antenna diversity operation modes

List of numerals

1 first antenna device port

2 second antenna device port

3 directional coupler 4 DPDT-switch

5 antenna

6 RF matching resistor

7 power detection device

8 second antenna

Cl ... C4 first coupler port to fourth coupler port

Cl input port

C2 direct port

C3 coupled port C4 isolated port

Sl ... S4 first switch port to fourth switch port

SWl ... SW4 first switch to fourth switch

A, B control lines

Claims

1. Antenna systeminterface circuit for transmitting and receiving signals in collocated wireless communication pathssystems integrated in a mobile device with a first part operating in a first wireless communication system provided with a first antenna device port (1) and a second part operating in a second wireless communication system provided with a second antenna device port (2), where the collocated wireless communication systems operate at least partially in the same frequency band, characterized in that a directional coupler (3) with four coupler ports (C 1 ... C4) where the first coupler port (Cl) is attached to the first antenna port (1) of the mobile device and with the thirdfourth coupler port (C34) to the second antenna port (2) of the mobile device and a DPDT switch (4) with four switch ports (Sl ... S4), four switches (SWl ... SW4) and two control lines (A; B) is attached with a first switch port (Sl) to the second coupler port (C2) and with the second switch port (S2) to the third coupler port (C3) and antenna (5) is connected with the third switch port (S3).

2. Antenna systeminterface circuit as claimed in claim 1, characterized in that the third switch port (S3) is connected to the antenna (5) and the fourth switch port (S4) is terminated by an RF matching element (6).

3. Antenna systeminterface circuit as claimed in claim 1 characterized in that the fourth switch port is terminated by a resistor (6) interposed between the fourth switch port (S4) and ground.

4. Antenna systeminterface circuit as claimed in one of the claims 1 to 3 characterized in that the fourth switch port (S4) is connected to an input of a power detection device (7).

5. Antenna systeminterface circuit as claimed in claim 1, characterized in that the third switch port (S3) is connected to the antenna (5) and the fourth switch port (S4) is connected to a second antenna (8).

6. Antenna systeminterface circuit as claimed in one of the claims 1 to 5, characterized in that the first part is operating in a wireless LAN (WLAN) system and the second part is operating in Bluetooth (BT) system.

7. Method for transmitting and receiving signals in collocated wireless communication systems where in a mobile device a first ystem wireless communication system receives and transmits signals via a first antenna device port (1) and a second wireless communication system receives and transmits signals via a second antenna device port (2), where the collocated wireless communication systems operate at least partially in the same frequency band, characterized in the following steps:

- providing the mobile device with a directional coupler (3) with four coupler ports (Cl ... C4);

- attaching the first coupler port (Cl) to the first antenna port (1) of the mobile device;

- attaching the thirdfourth coupler port (C34) to the second antenna port (2) of the mobile device;

- providing the mobile device with a DPDT switch (4) with four switch ports (Sl ... S4), four switches (SWl ... SW4) and two control lines (A; B);

- attaching a first switch port (Sl) to the second coupler port (C2) attaching the second switch port (S2) to the third coupler port (C3);

- connecting the antenna (5) with the third switch port (S3);

- controlling the switch (4) depending on the intended receiving or transmitting status of the first and the second part.

8. Method as claimed in claim 7 characterized in providing the DPDT (4) switch (4) with

a first switch (SWl) interposed between the first (Sl) and the third switch port (S3);

a second switch (SW2) interposed between the second (S2) and the fourth switch port (S4);

a third switch (SW3) interposed between the first (Sl) and the second switch port (S2);

a fourth switch (SW4) interposed between the second (S2) and the third switch port (S3);

- attaching the third switch port (S3) to the antenna (5);

- terminating the fourth switch port with an RF matching element (6);

- controlling the switch (4) depending on the intended receiving or transmitting status of the first and the second part as follows

9. Method as claimed in claim 7 characterized in

providing the DPDT switch (4) with a first switch (SWl) interposed between the first (Sl) and the third switch port (S3);

. a third switch (SW3) interposed between the first (Sl) and the second switch port (S2);

attaching the third switch port (S3) to the antenna (5);

terminating the fourth switch port (S4) with an RF matching element

(6);

- connecting the fourth switch port (S4) to a power detection device (7) measuring the output power in several measurement modes,

- controlling the switch (4) depending on the intended receiving or transmitting status of the first and the second part and depending on the intended measurement mode as follows

10. Method as claimed in claim 7 characterized in

providing the DPDT switch (4) with

a first switch (SWl) interposed between the first (Sl) and the third switch (S3);

. a fourth switch (S W4) interposed between the second (S2) and the third switch port (S3);

- attaching the third switch (S3) port to the antenna (5);

- connecting a second antenna (8) with the fourth switch port (S4);