Apparatus for protecting receiver in TDD wireless communication system

A Time Division Duplex (TDD) switch of a TDD wireless communication system is provided. By its unique arrangement, the TDD switch protects a receiver of the wireless system. The TDD switch includes an isolator connected to an output port of a transmitter, a first transmission line stub, connected between the isolator and a circulator, for transmitting a transmission signal received from the isolator when in a transmission mode, and for isolating a transmission path when in a reception mode, a first transmission line connected to the circulator, for isolating a reception path when in the transmission mode, and for supplying to a receiver a reception signal provided from an antenna connected to the circulator when in the reception mode, and a second transmission line stub connected between the first transmission line and an input port of the receiver in a stub form, for controlling the first transmission line to isolate the reception path when in the transmission mode, and for supplying the reception signal to the receiver when in the reception mode.

PRIORITY

This application claims the benefit under 35 U.S.C. §119(a) to a Korean patent application filed in the Korean Intellectual Property Office on Apr. 25, 2006 and assigned Serial No. 2006-37259, the entire disclosure of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a Time Division Duplex (TDD) switch of a TDD wireless communication system. More particularly, the present invention relates to an apparatus for protecting a receiver when a high-power transmission signal is incorrectly introduced into the receiver due to erroneous operations such as a malfunction of the TDD switch.

2. Description of the Related Art

In a Time Division Duplex (TDD) wireless communication system, a TDD switch is generally used for mode changes between a transmission mode and a reception mode. The TDD switch operates in response to a TDD control signal of the wireless communication system.

FIG. 1is a diagram illustrating a conventional location of a TDD switch in a TDD wireless communication system.

Referring toFIG. 1, a TDD switch107is connected to a Power Amplifier (PA)103, an antenna111, and a Low Noise Amplifier (LNA)115.

When the wireless communication system operates in a transmission mode, a signal from transmitter101is amplified to a high-power signal through the PA103and is then radiated through the antenna111via a transmit port105and an antenna port109. The TDD switch107operates in the transmission mode and thus isolates the transmitter101from a receiver117. Therefore, the receiver117can be protected against the high-power signal of the transmitter101.

When the wireless communication system operates in the reception mode, the power signal sent from the antenna111is received through the antenna port109and a receive port113. The TDD switch107operates in the reception mode and thus enables the received power signal to be sent to the receive port113. The received power signal has significantly low power due to attenuation and noise. Therefore, the power signal is amplified by the LNA115which amplifies a signal while minimizing noise. The amplified power signal is received by the receiver117.

FIG. 2is a diagram illustrating a conventional TDD switch.

Referring toFIG. 2, the conventional TDD switch includes an isolator203, a circulator205, a λ/4 transmission line209, a pin diode211, and so on. The λ/4 transmission line209and the pin diode211are interconnected between a receive port213and the circulator205.

In the conventional TDD switch shown inFIG. 2, the λ/4 transmission line209and the pin diode211are connected in a three connection configuration. The number of connection configurations of the λ/4 transmission line209and the pin diode211may be determined through simulation or theoretical calculation. In addition, the number of connection configurations may vary depending on the extent of isolation.

In the TDD wireless communication system, a transmitter including a PA may be connected to a transmit port201. A receiver including an LNA may be connected to the receive port213. Furthermore, an antenna may be connected to an antenna port207of the TDD switch.

The isolator203transmits a power signal only in one direction and is located between the transmit port201and the circulator205. The isolator203is designed to pass only the power signal transmitted from the transmit port201. Furthermore, the isolator203acts as a terminator for an external power signal that is reflected and returned. For example, when the power signal is not successfully radiated from the antenna and is thus reversely introduced, the circuit of the transmit port201may be damaged by the reflected power signal. Therefore, the isolator203protects the circuit of the transmit port201.

The circulator205is a 3-port circuit element for branching the power signal. A resonance plate and a magnetic substance (e.g., ferrite) are placed inside the circulator205having a shape in which three ports are arranged by 120 degrees. The circulator205incurs an approximately 0.3 dB path loss when passing the power signal in a direction from the isolator203to the antenna port207. Also, the circulator205isolates the power signal by a specific level (about 20 dB) in another direction from the circulator205to the receiver port213. For example, when the TDD control signal operates in the transmission mode, the power signal amplified by the transmitter exhibits an approximately 0.3 dB path loss while passing through the circulator205and is then radiated through the antenna via the antenna port207. In the direction from the circulator205to the receiver port213, the power signal is attenuated by a certain level (about 20 dB). Although the power signal is attenuated by the specific level (about 20 dB), the receive port213may be damaged when the attenuated signal is transmitted to the receive port213.

The TDD control signal is used to control the transmitter and the receiver of the TDD wireless communication system. In response to the TDD control signal, the transmitter amplifies a power signal to be transmitted and then radiates the amplified power signal to the antenna. In addition, the TDD control signal is used to control a bias circuit221which regulates a Direct Current (DC) bias supplied to the pin diode211. The DC bias is supplied to the pin diode211through a transmission line, but this does not affect wireless communication characteristics. The pin diode211acts as a part of the TDD switch according to the DC bias. A capacitor (not shown) is provided to block the DC bias. Although not shown, it will be assumed that the capacitor for blocking the DC bias exists throughoutFIGS. 2 to 6.

According to the transmission line theory, when an output port of a transmission line is open to ground, the impedance of the input port of the transmission line is expressed as Z=−jZo cot βl. When the output port of the transmission line is shorted to ground, the impedance of the input port of the transmission line is expressed as Z=−jZo tan βl. When the output port of the transmission line is connected to a 50 ohm transmission line, the impedance of the input port of the transmission line is expressed as Z=Zo=50 ohm. Here, β=2π/λ, and l is the length of the transmission line. As known, waves have the same amplitudes at λ/4, 3λ/4, 5λ/4, 7λ/4, and so on. Hence, the λ/4 transmission line209may be generalized as a (λ/4)*(2m+1) transmission line [m=0,1,2,3, . . . ]. The λ/4 transmission line209corresponds to a (λ/4)*(2m+1) transmission line [m=0,1,2,3, . . . ], where m is 0.

The pin diode211and the 50 ohm transmission line (receiver) are connected in parallel to the output port of the λ/4 transmission line209. The pin diode211acts as a part of the TDD switch according to the DC bias. When the impedance of the pin diode211becomes nearly 0 (short-circuited), the parallel impedance between the pin diode211and the 50 ohm transmission line becomes nearly 0 (short-circuited). On the other hand, when the impedance of the pin diode211becomes nearly infinite (open-circuited), the parallel impedance between the pin diode211and the 50 ohm transmission line becomes nearly 50 ohm. Therefore, impedance changes in the pin diode211according to the DC bias allow the output port of the λ/4 transmission line209to become substantially shorted to ground or substantially connected only to the 50 ohm transmission line.

When the pin diode211is substantially open to ground, the output port of the λ/4 transmission line209is nearly connected only to the 50 ohm transmission line. Thus, according to the above expression of Zo=50 ohm, the impedance Z of the input port of the λ/4 transmission line209becomes nearly 50 ohm.

When the output port of the λ/4 transmission line209is substantially shorted to ground, according to the above expression of Z=−jZo tan βl where β=2π/λ, and l=(λ/4)*(2m+1)[m=0,1,2,3, . . . ], the impedance Z of the input port of the λ/4 transmission line209becomes nearly infinite (open-circuited).

In the transmission mode, when the TDD control signal is transmitted to the bias circuit221, the bias circuit221supplies a forward DC bias to the pin diode211. The forward DC bias allows the impedance of the pin diode211to become nearly 0 (short-circuited). Since the output port of the λ/4 transmission line209is connected to the pin diode211, the impedance of the output port of the λ/4 transmission line209also becomes nearly 0 (short-circuited). Thus, the output port of the λ/4 transmission line209becomes substantially shorted to ground. According to the characteristic of the λ/4 transmission line209, the impedance of the input port of the λ/4 transmission line209(a port nearest to the circulator205) changes to be opposite to the impedance of the output port of the λ/4 transmission line209and thus becomes nearly infinite (open-circuited). Hence, the receive port213can be protected against the power signal while the TDD control signal operates in the transmission mode.

In the reception mode, when the TDD control signal is transmitted to the bias circuit221, the bias circuit221supplies a reverse DC bias to the pin diode211. The reverse DC bias allows the impedance of the pin diode211to become nearly infinite (open-circuited). Since the output port of the λ/4 transmission line209is connected to the pin diode211and the 50 ohm transmission line (receiver), when the impedance of the pin diode211becomes nearly infinite (open-circuited), the impedance of the output port of the λ/4 transmission line209becomes 50 ohm, and the impedance of the input port of the λ/4 transmission line209also becomes 50 ohm. Therefore, a path that spans from the antenna port207to the receive port213via the circulator205is not affected. Accordingly, most of the power signal received through the antenna can be input to the receive port213.

The TDD wireless communication system may operate correctly without any problem. However, when the TDD switch incorrectly operates, the TDD wireless communication system may operate in the transmission mode while the TDD switch operates in the reception mode. In this case, the power signal may not be completely isolated by the circulator205and thus may be introduced to the receiver, which may lead to damage in the circuit of the receiver.

Furthermore, a cable connected to the antenna port207may be open when the TDD switch is turned off, or a high-power signal may be reflected when a Voltage Standing Wave Ratio (VSWR) of the circuit of the transmitter increases due to impedance mismatching. In this case, most of the reflected high-power signal is introduced into the receiver, which may damage the circuit of the receiver. Impedance matching is used to reduce performance degradation caused by an impedance difference between two separate connection ports. The VSWR represents a reflection amount of the power signal transmitted to the antenna port207.

The DC bias of the bias circuit221cannot be supplied to the pin diode211when the TDD switch is turned off. This is similar to the case where the reverse DC bias is supplied to the pin diode211. Thus, the TDD switch operates in the reception mode.

The conventional TDD wireless communication system cannot operate correctly when the aforementioned problems occur mostly because the introduction of the power signal into the receiver may damage the circuit of the receiver. Accordingly, there is a need for a TDD switch that can protect the receiver even when the TDD wireless communication system operates incorrectly.

SUMMARY OF THE INVENTION

The present invention has been made to address the above-mentioned problems and/or disadvantages. Accordingly, an object of the present invention is to provide a Time Division Duplex (TDD) switch that protects a receiver in a wireless communication system.

Another object of the present invention is to provide a TDD switch that protects the receiver even when the TDD wireless communication system operates incorrectly due to errors.

According to one aspect of the present invention, an apparatus for protecting a receiver in a wireless communication system is provided. The apparatus includes a TDD switch in a wireless communication system comprising an isolator connected to an output port of a transmitter, a first transmission line stub which is connected between the isolator and a circulator, transmits a transmission signal received from the isolator when in a transmission mode, and isolates a transmission path when in a reception mode, a first transmission line which is connected to the circulator, isolates a reception path when in the transmission mode, and supplies to a receiver a reception signal provided from a antenna feed line connected to the circulator when in the reception mode and a second transmission line stub which is connected between the first transmission line and an input port of the receiver in a stub form, controls the first transmission line to isolate the reception path when in the transmission mode, and supplies the reception signal to the receiver when in the reception mode.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The present invention relates to a Time Division Duplex (TDD) switch for protecting a receiver of a TDD wireless communication system when operating not only correctly but also incorrectly due to errors.

FIG. 3is a diagram illustrating a TDD switch according to an exemplary embodiment of the present invention.

Referring toFIG. 3, the TDD switch includes an isolator303, a circulator305, pin diodes311and317, a λ/4 transmission line313, a λ/4 transmission line stub315, and a λ/2 transmission line stub309. The λ/2 transmission line stub309and the pin diode311are connected between the isolator303and the circulator305, thereby forming a TDD switch. The λ/4 transmission line313, the λ/4 transmission line stub315, and the pin diode317are connected between the circulator305and a receive port319, thereby forming another TDD switch. A plurality of TDD switches may be present, and the number of TDD switches may be determined through simulation or theoretical calculation. This will be described below with reference toFIGS. 5 and 6.

A transmission line is provided to transmit a high frequency signal. In a wireless communication system, the use of the high frequency signal may allow the transmission line itself to have a characteristic of a specific circuit element. In general, a transmission line stub having a specific length is perpendicularly attached to the transmission line. According to a connection state between the transmission line stub and ground, the transmission line stub may be either an open stub or a shorted stub. Similar to the transmission line, when used in a high frequency circuit, the transmission line stub may also have a characteristic of a specific circuit element. In addition, a λ/4 transmission line stub has the same characteristic as a λ/4 transmission line.

According to transmission line theory, when the output port of the transmission line stub is not connected to ground (i.e., open stub), the impedance of the input port of the transmission line stub is expressed as Z=−jZo cot βl. Further, when the output port of the transmission line stub is connected to ground (i.e., shorted stub), the impedance of the input port of the transmission line stub is expressed as Z=−jZo tan βl. Here, β=2π/λ, and l is the length of the transmission line stub. As known, waves have the same amplitudes at 0, λ/2, λ, 3λ/2, 2λ, and so on. Hence, the λ/2 transmission line stub309may be generalized as a (λ/2)*m transmission line stub [m=0,1,2,3, . . . ]. The λ/2 transmission line stub309corresponds to a (λ/2)*m transmission line stub [m=0,1,2,3, . . . ], where m is 1.

The output port of the λ/2 transmission line stub309is connected to the pin diode311. According to a DC bias of a bias circuit321, the pin diode311acts as a part of a TDD switch. Therefore, impedance changes in the pin diode311according to the DC bias allow the output port of the λ/2 transmission line stub309to become nearly shorted to or open to ground.

When the output port of the λ/2 transmission line stub309becomes substantially open to ground, according to the above expressions of Z=−jZo cot βl, β=2π/λ, and l=(λ/2)*m transmission line stub [m=0,1,2,3, . . . ], the impedance Z of the input port of the λ/2 transmission line stub309becomes nearly infinite (open-circuited). Since the input port of the λ/2 transmission line stub309and a 50 ohm transmission line are connected in parallel to the isolator303, when the impedance Z of the input port of the λ/2 transmission line stub309becomes nearly infinite (open-circuited), an input impedance viewed from the isolator303towards the circulator305becomes 50 ohm.

On the other hand, when the output port of the λ/2 transmission line stub309becomes substantially shorted to ground, according to the above expressions Z=−jZo cot ⊕l, β=2π/λ, and l=(λ/2)*m transmission line stub [m=0,1,2,3, . . . ], the impedance Z of the input port of the λ/2 transmission line stub309becomes nearly 0 (short-circuited).

In the transmission mode, when the TDD control signal is transmitted to the bias circuit321, the bias circuit321supplies a reverse DC bias to the pin diodes311and317. The reverse DC bias allows each of the impedances of the pin diodes311and317to become nearly infinite (open-circuited). Since the pin diode311located between the isolator303and the circulator305is connected to the output port of the λ/2 transmission line stub309, the impedance of the output port of the λ/2 transmission line stub309also becomes nearly infinite (open-circuited). Hence, the output port of the λ/2 transmission line stub309becomes substantially open to ground (open-circuited). Similar to the impedance of the output port of the λ/2 transmission line stub309, according to the characteristic of the λ/2 transmission line stub309, the impedance of the input port (a port nearest to the isolator303) of the λ/2 transmission line stub309becomes nearly infinite (open-circuited). Accordingly, an input impedance viewed from the isolator303towards the circulator305becomes 50 ohm.

When the TDD control signal operates in the transmission mode, the reverse DC bias allows the impedance of the pin diode317located between the circulator305and the receive port319to become nearly infinite (open-circuited). Since the pin diode317is connected to the output port of the λ/4 transmission line stub315, the impedance of the output port of the λ/4 transmission line stub315also becomes nearly infinite (open-circuited). Hence, the output port of the λ/4 transmission line stub315becomes substantially open to ground (open-circuited). The impedance of the input port of the λ/4 transmission line stub315is nearly 0 (short-circuited), similar to that of the λ/4 transmission line209ofFIG. 2. The impedance of the output port of the λ/4 transmission line313becomes nearly 0 (short-circuited) since it is a parallel impedance between the impedance of the input port of the λ/4 transmission line stub315and the impedance of the 50 ohm transmission line. The impedance of the input port (a port nearest to the circulator305) of the λ/4 transmission line313becomes nearly infinite (open-circuited) according to the characteristic of the λ/4 transmission line313. Therefore, it is possible to isolate most of the power signal to be supplied from the circulator305from the receive port319while the wireless communication system operates in the transmission mode, thereby protecting the circuit of the receiver.

Consequently, when the wireless communication system operates in the transmission mode, the λ/2 transmission line stub309and the pin diode311operate as if they do not exist, and the receive port319is protected by the λ/4 transmission line313, the λ/4 transmission line stub315, and the pin diode317. Therefore, the wireless communication system can perform a transmission operation without damaging the receiver.

In the reception mode, when the TDD control signal is transmitted to the bias circuit321, the bias circuit321supplies a forward DC bias to the pin diodes311and317. The forward DC bias allows each of the impedances of the pin diodes311and317to become nearly 0 (short-circuited). Since the pin diode311located between the isolator303and the circulator305is connected to the output port of the λ/2 transmission line stub309, the impedance of the output port of the λ/2 transmission line stub309also becomes nearly 0 (short-circuited). Hence, the output port of the λ/2 transmission line stub309becomes substantially shorted to ground (short-circuited). Similar to the impedance of the output port of the λ/2 transmission line stub309, according to the characteristic of the λ/2 transmission line stub309, the impedance of the input port (a port nearest to the isolator303) of the λ/2 transmission line stub309becomes nearly 0 (short-circuited). Since the input port of the λ/2 transmission line stub309and the 50 ohm transmission line are connected in parallel to the isolator303, when the impedance Z of the input port of the λ/2 transmission line stub309becomes nearly 0 (short-circuited), the input impedance viewed from the isolator303towards the circulator305becomes nearly 0 (short-circuited). If the TDD switch incorrectly operates, the TDD wireless communication system may operate in the transmission mode while the TDD switch operates in the reception mode. In this case, the high-power signal amplified by the transmitter and transmitted by transmission port301is reflected by the pin diode311and is returned to the isolator303, thereby being terminated. Therefore, the circuit of the receiver can be protected.

When the TDD control signal operates in the reception mode, the forward DC bias also allows the impedance of the pin diode317located between the circulator305and the receive port319to become nearly 0 (short-circuited). Since the pin diode317is connected to the output port of the λ/4 transmission line stub315, the impedance of the output port of the λ/4 transmission line stub315also becomes nearly 0 (short-circuited). Therefore, the output port of the λ/4 transmission line stub315becomes substantially shorted to ground (short-circuited). According to the characteristic of the λ/4 transmission line stub315, the impedance of the input port of the λ/4 transmission line stub315changes to be opposite to the impedance of the output port of the λ/4 transmission line stub315and thus becomes nearly infinite (open-circuited). Since the input port of the λ/4 transmission line stub315and the 50 ohm transmission line are connected in parallel to the output port of the λ/4 transmission line313, the impedance of the output port of the λ/4 transmission line313becomes 50 ohm. As a result, the impedance of the input port (a port nearest to the circulator305) of the λ/4 transmission line313becomes 50 ohm according to the characteristic of the λ/4 transmission line313.

Consequently, when the wireless communication system operates in the reception mode, according to the operations of the λ/2 transmission line stub309and the pin diode311, an output of the isolator303is reflected, and the reflected output is returned to the isolator303, thereby being terminated. Therefore, even if an abnormal output is produced from the isolator303, the receive port319can be protected. In addition, the λ/4 transmission line313, the λ/4 transmission line stub315, and the pin diode317enable the receive port319to receive a signal received through the antenna port307.

If the TDD switch operates incorrectly, the TDD wireless communication system may operate in the transmission mode while the TDD switch operates in the reception mode. In this case, the high-power transmission signal is reflected by the operations of the pin diode311and the λ/2 transmission line stub309and is thus returned to the isolator303, thereby being terminated. Therefore, the circuit of the receiver can be protected.

A cable connected to the antenna port307may be open when the TDD switch is turned off, or a high-power signal may be reflected when a Voltage Standing Wave Ratio (VSWR) of the circuit of the antenna increases due to impedance mismatching. Even in this case, the pin diode317, the λ/4 transmission line stub315, and the λ/4 transmission line313operate in the same state as when the TDD switch operates in the transmission mode. Therefore, most of the power signal to be introduced into the receive port319is isolated, thereby protecting the circuit of the receiver.

FIG. 4is a diagram illustrating a TDD switch without a λ/2 transmission line stub according to an exemplary embodiment of the present invention. Referring toFIG. 4, the TDD switch includes an isolator403, a circulator405, pin diodes411and417, a λ/4 transmission line413and a λ/4 transmission line stub415. The λ/4 transmission line413, the λ/4 transmission line stub415, and the pin diode417are connected between the circulator405and a receive port419. The exemplary embodiment illustrated inFIG. 4also includes a transmission port401, an antenna port407and a bias circuit421.

As illustrated inFIG. 4, an exemplary embodiment includes a generalized (λ/2)*m transmission line stub [m=0,1,2,3, . . . ] when m is 0. According to transmission line theory, the transmission line stub has a specific length, and waves have the same amplitudes at 0, λ/2, λ, 3λ/2, 2λ, and so on. Therefore, the λ/2 transmission line stub may be generalized as a (λ/2)*m transmission line stub [m=0,1,2,3, . . . ]. As a result, a high frequency system such as the TDD wireless communication system has the same characteristic regardless of whether the λ/2 transmission line stub is absent or whether the transmission line stub has the length of λ/2, λ, 3λ/2, 2λ, and so on.

Accordingly, an exemplary TDD switch without the λ/2 transmission line stub as shown inFIG. 4operates in the same manner as the TDD switch with the λ/2 transmission line stub309as illustrated inFIG. 3.

FIG. 5is a diagram illustrating a TDD switch having three connection configurations each of which includes a λ/4 transmission line, a λ/4 transmission line stub, and a λ/2 transmission line stub according to an exemplary embodiment of the present invention.

Referring toFIG. 5, a connection configuration A516includes a λ/4 transmission line513, a λ/4 transmission line stub514, and a pin diode515. In the connection configuration A516, the function of the λ/4 transmission line513is similar to that of the λ/4 transmission line313ofFIG. 3, and the function of the λ/4 transmission line stub514is similar to that of the λ/4 transmission line stub315. In addition, the function of the pin diode515is similar to that of the pin diode317ofFIG. 3. Likewise, connection configurations B517and C518each includes a λ/4 transmission line, a λ/4 transmission line stub, and a pin diode each having the same functions as those in the connection configuration A516. As further illustrated inFIG. 5, an exemplary embodiment may also include a transmission port501, an isolator503, an antenna port507, a λ/2 transmission line stub509, a PIN diode511and a bias circuit521.

The number of connection configurations may vary depending on the extent of isolation between a circulator505and a receive port519. Further, the number of connection configurations may be determined through simulation or theoretical calculation.

FIG. 6is a diagram illustrating an exemplary TDD switch having three connection configurations each of which includes a λ/4 transmission line613, a λ/4 transmission line stub615, and a pin diode617. However, in the exemplary embodiment illustrated inFIG. 6, a λ/2 transmission line stub is absent.

InFIG. 6, the configuration of a circuit located between a circulator605and a receive port619is the same as that ofFIG. 5. Similar toFIG. 4, the TDD switch ofFIG. 6does not have the λ/2 transmission line stub. As further illustrated inFIG. 6, the exemplary embodiment also includes a transmission port601, an isolator603, an antenna port607, a PIN diode611and a bias circuit621.

For example, the TDD switch for protecting the receive port619may employ the configuration shown inFIG. 4, which is the same as the configuration shown inFIG. 3except that the λ/2 transmission line stub is absent, when the TDD switch operates in the reception mode while the TDD wireless communication system operates in the transmission mode. Further, the TDD switch for protecting the receive port619may employ the configuration shown inFIG. 5, when the TDD switch is turned off.

Accordingly, when the TDD switch operates in the reception mode while the TDD wireless communication system operates in the transmission mode, or when the switch of the TDD wireless communication system is turned off, the circuit of the receiver can be protected.