WO2019110082A1

WO2019110082A1 - Radio frequency front end for wireless communication

Info

Publication number: WO2019110082A1
Application number: PCT/EP2017/081352
Authority: WO
Inventors: Dror Regev; Shimon SHILO; Doron Ezri
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2017-12-04
Filing date: 2017-12-04
Publication date: 2019-06-13

Abstract

A radio frequency front end for wireless communication comprises an antenna port (111), a transmit path (120) having a transmit path output (121), a receive path (130) having a receive path input (131), a transmit/receive switch (140) connected with a first terminal (141) to the receive path input (131), and an isolation device (150) connected to the antenna port (111), the transmit path output (121), and a second terminal (142) of the transmit/receive switch. The isolation device (150) is configured to isolate the second terminal (142) of the transmit/receive switch (140) from the transmit path output (141), to supply a transmit signal (122) from the transmit path output (121) to the antenna port (111), and to supply a receive signal (132) from the antenna port (111) to the second terminal (142) of the transmit/receive switch (140).

Description

TITLE

Radio frequency front end for wireless communication

FIELD OF THE INVENTION The present invention relates to a radio frequency front end for wireless communication, especially to a radio frequency front end in which transmitting and receiving is performed using the same antenna.

BACKGROUND There are different operation modes for a radio frequency front end in which transmitting and receiving is performed using the same antenna. In a half-duplex system (HD), also known as transmit/receive (TR), only one of transmitting and receiving can be performed at a specific time. In a full-duplex system (FD), also known as simultaneous transmit/receive (STR), both transmitting and receiving may be performed simultaneously. In the half-duplex system, the antenna is either connected to an output port of a transmit path which is adapted to supply a transmit signal which is to be transmitted via the antenna, or to an input port of a receive path which is adapted to process a receive signal received from the antenna. In the full- duplex system, the antenna is permanently connected both to the output port of the transmit path and the input port of the receive path. Fig. 3 shows a schematic circuit diagram of a conventional radio frequency front end for half-duplex operation. The radio frequency front end 300 comprises an antenna port 311 to which an antenna 310 is connected. The radio frequency front end 300 further comprises a transmit path 320 for supplying a transmit signal 322 to the antenna port, and a receive path 330 for receiving a receive signal 332 from the antenna port 311. The transmit path 320 comprises an output amplifier 323, for example a power amplifier, the output of which is connected to a transmit path output 321. The receive path 330 comprises an input amplifier 333, for example a low-noise amplifier, the input of which is connected to a receive path input 331.

A transmit/receive switch 350 is connected to the antenna port 311, the transmit path output 321, and the receive path input 331. The transmit/receive switch is configured to connect the antenna port 311 either to the transmit path output 321 or to the receive path input 331. In a transmit mode, the signal switch 350 connects the antenna port 311 to the transmit path output 321 so that the transmit signal 322 may be supplied to the antenna port. In a receive mode, the signal switch 350 connects the antenna port 311 to the receive path input 331 so that the receive signal 332 may be received from the antenna port 311.

A further function of the transmit/receive switch 350 is to protect the input amplifier 333 from a damage caused by the high power of the transmit signal 322 by isolating the receive path 330 from the transmit path 320 during the transmit mode. Further, it avoids that the transmit path 320 or the receive path 330 are a load for the respective other path so that they do not negatively affect each other. Since the transmit/receive switch 350 supplies the full transmit signal 322 to the antenna port 311, it has to be rated for the maximum transmit power and therefore becomes bulky with relatively high power loss and expensive.

Fig. 4 shows a schematic circuit diagram of a conventional radio frequency front end for full-duplex operation. Similar as the radio frequency front end 300, the radio frequency front end 400 comprises an antenna port 411 to which an antenna 410 is connected, a transmit path 420 for supplying a transmit signal 422 to the antenna port, and a receive path 430 for receiving a receive signal 432 from the antenna port. The transmit path 420 comprises an output amplifier 423, for example a power amplifier, the output of which is connected to a transmit path output 421. The receive path 430 comprises an input amplifier 433, for example a low-noise amplifier, the input of which is connected to a receive path input 431.

A circulator 450 is connected to the antenna port 411, the transmit path output 421, and the receive path input 431. Circulators are usually three-port devices that transfer a signal either clockwise or counter clockwise from port to port while isolating the signal from traveling in the reverse direction. Thus, the transmit signal 422 can be supplied from the transmit path output 421 to the antenna port 411, and the receive signal 432 can be supplied from the antenna port 411 to the receive path input 431. Flowever, the transmit signal 422 is inhibited from reaching the receive path input 431, or at least is attenuated. This isolation is typically in the range of 15 dB so that an attenuated portion of the transmit signal 422 still reaches the receive path input 431. Another portion of the transmit signal 422 may be reflected by the antenna 410 and reach the receive path input 431 via the circulator 450 using the signal path provided for the receive signal 432.

To improve the isolation of the receive path 430 from the transmit path 420, the radio frequency front end 400 further comprises a divider 460 for branching-off a portion 461 from the transmit signal 421, a filter 470 for processing the branched-off portion 461, and a combiner to combine the processed branched-off portion 471 with a signal at the receive path input 432. The filter 470 is an self-interference cancellation filter (SIC) filter configured to process the branched-off portion 461 so that it will cause self-interference cancellation with the portions of the transmit signal 422 that have reached the receive path input 432. Such a full-duplex front-end having a second stage of cancellation is for example described in "Full Duplex Radios", by: Dinesh Bharadia, Emily McMilin, Sachin Katti, Stanford University, in Proceedings of the ACM SIGCOMM 2013 conference on SIGCOMM, Pages 375-386.

An advantage of a full-duplex front end is that by the simultaneous transmit/receive mode, the channel throughput theoretically may be doubled. On the other hand, there are disadvantages in that there are additional power losses at the transmit path and the receive path due to the elements used for the self-interference cancellation, that additional hardware is required and that additional space on the printed circuit board is required. Even if a full-duplex front end as shown in Fig. 4 can also support half-duplex operation, the half-duplex performance is reduced by these losses in comparison to a half-duplex front end as shown in Fig. 3.

It is therefore desirable to enable switching between a full-duplex operation, if this feature is required, taking into account the reduced performance of this operation mode, and half-duplex operation, if full-duplex operation is not required, but then with the performance of a half-duplex front end. Desired attributes of such a dual-mode front end are, among others: · Adequate transmit power handling

• Good transmit/receive isolation

• Low insertion loss on both transmit and receive paths

SUMMARY It is therefore an object of the present invention to provide a dual-mode radio frequency front end that supports both full-duplex operation and half-duplex operation, wherein half-duplex is performed as good as or better than by a half-duplex front end, while full-duplex is performed with the best possible performance. The foregoing and other objects are achieved by the features of the independent claims. Further implementation forms are apparent from the dependent claims, the descriptions and the figures.

According to a first aspect, a radio frequency front end for wireless communication is provided. The radio frequency front end comprises an antenna port configured to connect an antenna, a transmit path comprising a transmit path output for a transmit signal to be supplied to the antenna port, a receive path comprising a receive path input for a receive signal to be received from the antenna port, a transmit/receive switch connected with a first terminal to the receive path input, and an isolation device connected to the antenna port, the transmit path output, and a second terminal of the transmit/receive switch, and configured to isolate the second terminal of the transmit/receive switch from the transmit path output. The isolation device is further configured to supply the transmit signal from the transmit path output to the antenna port, and to supply the receive signal from the antenna port to the second terminal of the transmit/receive switch.

With such a radio frequency front end it is possible, for example, to perform both full-duplex operation and half-duplex operation. In the full-duplex operation mode, the quality with regard to power handling and insertion losses is comparable with the one of known full-duplex front end concepts. In the half-duplex operation mode, however, the quality may even be better than with a conventional half-duplex front end because the transmit/receive switch used does not have to be of a high-power and high-isolation type.

In an implementation form of the first aspect, the radio frequency front end is further adapted to close the transmit/receive switch when the radio frequency front end is in a full-duplex operation mode or in a half-duplex receive operation mode, and/or to open the transmit/receive switch when the radio frequency front end is in a half-duplex transmit operation mode.

Thereby it is possible, for example, to adapt the radio frequency front end to the required operation mode in an optimum way. In the half-duplex transmit operation mode, the opened transmit/receive switch provides an additional isolation between the transmit and receive path.

In a further implementation form of the first aspect, the isolation device comprises a circulator.

Thereby it is possible, for example, to provide the required isolation with a common commercially available component. In a further implementation form of the first aspect, the isolation device comprises an output stage of a quadrature balanced amplifier having a transmit signal output port connected to the antenna port and an output isolated port connected to the second terminal of the transmit/receive switch.

Thereby it is possible, for example, to provide the required isolation with an electronic circuit, without having to use bulky elements such as a circulator.

In a further implementation form of the first aspect, the radio frequency front end further comprises a signal subtracting device configured to branch-off a first portion of the transmit signal, a filter configured to process the branched-off first portion of the transmit signal, and a signal adding device configured to add the processed branched-off first portion of the transmit signal at the receive path input.

Thereby it is possible, for example, to introduce a stage of cancellation between the transmit path and the receive path as a second stage in addition to the first stage provided by the isolation device.

In a further implementation form of the first aspect, the filter is a self-interference cancellation (SIC) filter configured to process the branched-off first portion of the transmit signal in a way that it causes self interference cancellation with a second portion of the transmit signal that has reached the receive path input via the isolation device.

Thereby it is possible, for example, to further reduce a second portion of the transmit signal that has reached the receive path input. This second portion may for example be a residual portion due to a limited isolation of the isolation device itself or a reflected portion that is reflected back from the antenna to the receive path. The way the first portion is processed may be to mimic the transfer function of the isolator leakage and the antenna reflection. Cancellation may then be achieved through combining this very similar signals with an opposite phase.

In a further implementation form of the first aspect, the signal subtracting device comprises a first switching unit that is configured to switch between a first state in which the transmit signal is entirely supplied to the antenna port and a second state in which the first portion of the transmit signal is branched-off towards the filter.

Thereby it is possible, for example, to disconnect the signal subtracting device in a case in which it is not required.

In a further implementation form of the first aspect, the signal adding device comprises a second switching unit that is configured to switch between a third state in which the filter is isolated from the receive path input and a fourth state in which the processed branched-off portion of the transmit signal is added at the receive path input.

Thereby it is possible, for example, to disconnect the signal adding device in a case in which it is not required. In a further implementation form of the first aspect, the radio frequency front end is configured to switch the first switching unit into the first state and/or the second switching unit into the third state in a half-duplex receive operation mode and/or a half-duplex transmit operation mode, and/or to switch the first switching unit into the second state and/or the second switching unit into the fourth state in a full-duplex operation mode. Thereby it is possible, for example, to disconnect the stage of cancellation in a case in which it is not required such as in the half-duplex receive operation mode in which no transmit signal is present or in the half-duplex transmit operation mode in which the opened transmit/receive switch provides an additional isolation. Thereby it is possible to avoid that the stage of cancellation is a load for the transmit and receive path, and thereby to avoid the losses involved on both transmit and receive path while operating in the half-duplex receive or transmit operation mode.

In a further implementation form of the first aspect, an antenna is connected to the antenna port.

Thereby it is possible, for example, to transmit the transmit signal and receive the receive signal via the same antenna.

The above object is also achieved in accordance with a second aspect. According to the second aspect, a method for operating a radio frequency front end for wireless communication is provided. The method comprises supplying a receive signal from an antenna port via an isolation device and a transmit/receive switch to a receive path input of a receive path, and/or supplying a transmit signal from a transmit path output of a transmit path to an antenna port via the isolation device and isolating the transmit/receive switch from the transmit path output by the isolation device.

With such a method it is possible, for example, to perform both full-duplex operation and half-duplex operation. In the full-duplex operation mode, the quality with regard to power handling and insertion losses is comparable with the one of known full-duplex front end concepts. In the half-duplex operation mode, however, the quality may even be better than with a conventional half-duplex front end because the transmit/receive switch used does not have to be of a high-power and high-isolation type.

In an implementation form of the second aspect, the method further comprises closing the transmit/receive switch when the radio frequency front end is in a full-duplex operation mode or in a half-duplex receive operation mode, and/or opening the transmit/receive switch when the radio frequency front end is in a half-duplex transmit operation mode.

Thereby it is possible, for example, to adapt the radio frequency front end to the required operation mode in an optimum way. In the half-duplex transmit operation mode, the opened transmit/receive switch provides an additional isolation between the transmit and receive path. In a further implementation form of the second aspect, the isolation device comprises a circulator.

Thereby it is possible, for example, to provide the required isolation with a common commercially available component.

In a further implementation form of the second aspect, the isolation device comprises an output stage of a quadrature balanced amplifier having a transmit signal output port connected to the antenna port and an output isolated port connected to the second terminal of the transmit/receive switch.

In a further implementation form of the second aspect, the method further comprises branching-off a first portion of the transmit signal, processing the branched-off first portion of the transmit signal, and adding the processed branched-off first portion of the transmit signal at the receive path input.

Thereby it is possible, for example, to introduce an additional isolation between the transmit path and the receive path as a second stage in addition to the isolation provided by the isolation device.

In a further implementation form of the second aspect, the branched-off first portion of the transmit signal is processed in a way that it causes self interference cancellation with a second portion of the transmit signal that has reached the receive path input.

Thereby it is possible, for example, to further reduce a portion of the transmit signal that has reached the receive path input. This second portion may for example be a residual portion due to a limited isolation of the isolation device itself or a reflected portion that is reflected back from the antenna to the receive path. The way the first portion is processed may be to mimic the transfer function of the isolator leakage and the antenna reflection. Cancellation may then be achieved through combining this very similar signals with an opposite phase.

In a further implementation form of the second aspect, the method further comprises switching into a state in which the transmit signal is entirely supplied to the antenna port and/or no signal is added to the signal at the receive path input in a half-duplex receive operation mode and/or a half-duplex transmit operation mode, and/or switching into a state in which a portion of the transmit signal is branched-off and/or a processed branched-off portion of the transmit signal is added to the signal at the receive path input in a full-duplex operation mode.

Thereby it is possible, for example, to disconnect the second stage of cancellation in a case in which it is not required such as in the half-duplex receive operation mode in which no transmit signal is present or in the half-duplex transmit operation mode in which the opened transmit/receive switch provides an additional isolation. Thereby it is possible to avoid that the stage of cancellation is a load for the transmit and receive path, and thereby to avoid the losses involved on both transmit and receive path while operating in the half-duplex receive or transmit operation mode.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic circuit diagram of a radio frequency front end according to an embodiment of the present invention.

Fig. 2 is a schematic circuit diagram of a radio frequency front end according to another

embodiment of the present invention.

Fig. 3 is a schematic circuit diagram of a conventional radio frequency front end for half-duplex operation.

Fig. 4 is a schematic circuit diagram of a conventional radio frequency front end for full-duplex operation. DETAILED DESCRIPTION

In the following, embodiments of the invention are described with reference to the enclosed figures.

Fig. 1 shows a schematic circuit diagram of a radio frequency front end according to an embodiment. The radio frequency front end 100 comprises an antenna port 111 to which an antenna 110 is connected. The radio frequency front end 100 further comprises a transmit path 120 for supplying a transmit signal 122 to the antenna port, and a receive path 130 for receiving a receive signal 132 from the antenna port. The transmit path 120 comprises an output amplifier 123, for example a power amplifier, the output of which is connected to a transmit path output 121. The receive path 130 comprises an input amplifier 133, for example a low-noise amplifier, the input of which is connected to a receive path input 131.

The radio frequency front end 100 further comprises a transmit/receive switch 140 and a circulator 150. The transmit/receive switch 140 is a simple circuit breaker that may be switched on or off. A first terminal 141 of the transmit/receive switch 140 is connected to the receive path input 131. The circulator 150 is connected to the antenna port 111, the transmit path output 121, and a second terminal 142 of the transmit/receive switch 140.

If an improved isolation of the receive path 130 from the transmit path 120 in the full-duplex operation is required, the radio frequency front end 100 may further comprise a signal subtracting device 160 configured to branch-off a first portion 161 of the transmit signal 122, a filter 170 configured to process the branched-off first portion 161 of the transmit signal, and a signal adding device 180 configured to add the processed branched-off first portion 171 of the transmit signal at the receive path input 131. Signal subtraction or addition may for example be performed by directional couplers, but the present invention is not restricted thereto. The filter 170 preferably is an SIC filter configured to process the branched-off portion 161 by mimicking the transfer function of the isolator leakage and the antenna reflection. This makes it possible to achieve that the processed signal 171 has almost the same amplitude, but an inverse phase than a sum of the portions of the transmit signal 122 that have reached the receive path input 131, thereby causing a self-interference cancellation. This self-interference cancellation is preferably designed to be strong enough to reduce the portions of the transmit signal 122 that have reached the receive path input 131 to below the noise floor level at the antenna. Contrary to the prior art described above, the signal subtracting device 160 and the signal adding device 180 can be switched between a state in which signal subtraction or addition is performed, and a state in which the transmit signal and or the receive signal are transmitted without change. This is symbolically indicated in Fig. 1 by switching units 162, 182 interrupting the signal path. The present invention, however, is not restricted to this type of switching. As the signal subtracting device 160, any device may be used that is adapted to switch between a state in which the transmit signal 122 is entirely supplied to the antenna port 111 and a state in which the first portion 161 of the transmit signal 122 is branched-off towards the filter 170. As the signal adding device 180, any device may be used that is adapted to switch between a state in which the filter 170 is isolated from the receive path input 131 and a state in which the processed branched-off portion 171 of the transmit signal is added at the receive path input 131.

The operation of the radio frequency front end 100 will be described next. Basically, a dual-mode radio frequency front end that supports both full-duplex operation and half-duplex operation has three operation modes: full-duplex operation mode, half-duplex receive operation mode, or half duplex transmit operation mode.

In the full-duplex operation mode, the transmit/receive switch 140 is closed. Thereby it is possible to simultaneously perform transmitting and receiving. An insulation between the transmit path and the receive path is provided by the circulator 150.

If an improved isolation is required, the signal subtracting device 160 and the signal adding device 180 can be switched into a state in which the first portion 161 of the transmit signal 122 is branched- off towards the filter 170 and the processed branched-off portion 171 of the transmit signal is added at the receive path input 131 so that a self-interference cancellation is performed. In this case, the performance of the radio frequency front end 100 corresponds to the one of the full-duplex front end 400 shown in Fig. 4.

Flowever, if an improved isolation is not required, the signal subtracting device 160 and the signal adding device 180 can be switched into a state in which the transmit signal 122 is entirely supplied to the antenna port 111, and the filter 170 is isolated from the receive path input 131. Thereby, the losses caused by the signal subtracting device 160 and the signal adding device 180 are avoided so that the performance of the radio frequency front end 100 even is better than the one of the full- duplex front end 400 shown in Fig. 4. Also in the half-duplex receive operation mode, the transmit/receive switch 140 is closed. An insulation between the transmit path and the receive path is not required because no transmit signal 122 is generated.

Only in the half-duplex transmit operation mode, the transmit/receive switch 140 is opened. An insulation between the transmit path and the receive path is provided both by the circulator 150 and the opened transmit/receive switch 140. The insulation is therefore increased in comparison with a full-duplex front end.

In the half-duplex receive operation mode and in the half-duplex transmit operation mode, an improved insulation between the transmit path and the receive path is therefore not required. Therefore, the signal subtracting device 160 and the signal adding device 180 can be switched into a state in which the in which the transmit signal 122 is entirely supplied to the antenna port 111 and the filter 170 is isolated from the receive path input 131 whereby the losses caused by the signal subtracting device 160 and the signal adding device 180 are avoided.

The transmit/receive switch 140 of the embodiment only has to switch the receive signal. It therefore does not have to be rated for the maximum transmit power and may be smaller and less expensive than in a half-duplex front end. It therefore also has a lower loss which is, however, only present in the receive path while the transmit power is only affected by the low loss circulator.

Therefore, the performance of the radio frequency front end in the half-duplex operation mode even is better than the one of the half-duplex front end 300 shown in Fig. 3.

This shall be illustrated by a numerical example: A typical transmit/receive switch for a half-duplex front end has, for a signal frequency of 5 GHz, an insertion loss of -1.1 dB both in the transmit path and in the receive path, as well as an isolation of -25 dB. A typical circulator has, for a signal frequency of 5 GHz, an insertion loss of -0.4 dB. This results in a loss of -0.4 dB for the transmit path, and together with the loss of the low-power transmit/receive switch 140 of the embodiment in a loss of less than 1 dB for the receive path. The isolation is -15 dB by the circulator, to which the isolation of the transmit/receive switch 140 is to be added.

The present invention thus enables a dual mode operation while maintaining or improving the performance of the known single mode architectures.

In the embodiment of Fig. 1, a circulator is used for providing an insulation between the transmit path and the receive path. The present invention, however, is not restricted to the use of a circulator for this purpose. Any isolation device may be used that is capable to isolate the second terminal of the transmit/receive switch from the transmit path output, while it is also capable to supply the transmit signal from the transmit path output to the antenna port, and to supply the receive signal from the antenna port to the second terminal of the transmit/receive switch.

Merely as an example, Fig. 2 shows a schematic circuit diagram of a radio frequency front end according to an embodiment wherein another isolation device is used.

Also the radio frequency front end 200 comprises an antenna port 211 to which an antenna 110 is connected, a transmit path 220 for supplying a transmit signal to the antenna port, and a receive path 130 for receiving a receive signal from the antenna port. The transmit path 120 comprises an output amplifier 250 which is realized as a quadrature balanced power amplifier. The receive path 230 comprises an input amplifier 233, for example a low-noise amplifier, the input of which is connected to a receive path input 231. A first terminal 241 of a transmit/receive switch 240 also is connected to the receive path input 231.

The quadrature balanced power amplifier 250 has a signal input port 251 to which an input signal is supplied, an input isolated port 252 to which a termination element 258 is connected, a signal output port 253 which is connected to the antenna port 211, and an output isolated port 254 which is connected to a second terminal 242 of a transmit/receive switch 240.

The quadrature balanced power amplifier 250 comprises an input coupler 255, two power amplifiers 256a, 256b, and an output coupler 257. A first input of the input coupler 255 is connected to the signal input port 251, and a second input is connected to the input isolated port 252. A first output of the input coupler 255 is connected to an input of the first power amplifier 256a, and a second output of the input coupler 255 is connected to an input of the second power amplifier 256b. An output of the first power amplifier 256a is connected to a first input of the output coupler 257, and an output of the second power amplifier 256b is connected to a second input of the output coupler 257. A first output of the output coupler 257 is connected to the signal output port 253, and a second output of the output coupler 257 is connected to the output isolated port 254.

The input coupler 255 may be a 3dB/90° coupler that divides an input signal into two output signals having the same amplitude and thus a signal level reduced by 3dB with regard to the input signal 131, and a relative phase of 90° with regard with each other. The output coupler 257 also may be a 3dB/90° coupler that divides each of its input signals into two components having the same amplitude and a phase shift of 90° with regard to each other. Two signal paths are thus provided between the signal input port 251 and each of the signal output port 253 and the output isolated port 254.

In the transmit operation, the signals of the two signal paths reaching the signal output port 253 each have been subjected to one phase shift by 0° and one phase shift of 90°. They therefore are in phase and constructively interfere with each other to form by their addition the transmit signal. At the output isolated port 254, however, the signal of the one signal path has twice been subjected to a relative phase shift of 0°, and the signal of the other signal path has twice been subjected to a relative phase shift of 90°. Therefore, the two components have a phase difference of 180° and destructively interfere with each other to cancel each other. Thus, the isolation between the signal output port 253 and the output isolated port 254 is achieved without that any further element such as a signal switch or a circulator is required for this purpose. Additional isolation is provided in the half-duplex transmit mode by the transmit/receive switch 240 which is opened during this operation mode.

In the receive operation, a signal delivered by the antenna port 211 to the signal output port 253 propagates through the output coupler 257 in its reverse direction and is divided into two output signals having the same amplitude and a relative phase of 90° with regard with each other. The components are then reflected at the outputs of the power amplifiers 256a, 256b. Each of the reflected components again is divided by the output coupler 257 into two output signals having the same amplitude and a relative phase of 90° with regard with each other. Two signal paths are thus provided between the signal output port 253 back to the signal output port 253 as well as to the output isolated port 254.

At the output isolated port 254, the signals of the two signal paths each have been subjected to one phase shift by 0° and one phase shift of 90°. They therefore are in phase and constructively interfere with each other to form by their addition the receive signal that is supplied to the receive path input 231. Since the output reflection coefficients of power amplifiers generally are very high and thus the reflection losses very low, the insertion loss of the path from the antenna port 211 to the receive path input 231 can also be very low. The power amplifiers 256a, 256b may also especially be designed to have a large output reflection coefficient not only at small signal operation, but also at large signal operation.

At the signal output port 253, however, the signal of the one signal path has twice been subjected to a relative phase shift of 0°, and the signal of the other signal path has twice been subjected to a relative phase shift of 90°. Therefore, the two components have a phase difference of 180° and destructively interfere with each other to cancel each other. The input reflection in the receive mode therefore is very low.

If an improved isolation of the receive path 230 from the transmit path 220 in the full-duplex operation is required, the radio frequency front end 200 may also comprise a switchable self interference cancellation path 260 which is similar to the one realized in the radio frequency front end 100 by elements 160 to 180 and which is operated as described above.

It is pointed out that the present invention is not limited to the exact circuit structure of the quadrature balanced amplifier described above. For example, more than two power amplifiers may be provided which are, for example, divided into two groups. The power amplifiers of the same group may be connected in parallel, for example by directly connecting the inputs in parallel and by connecting the outputs in parallel, or by using equal phase dividers and combiners at the input and output side, respectively, so that each of the two groups of power amplifiers corresponds to one of the power amplifiers 256a, 256b of Fig. 2.

On the other hand, the quadrature balanced power amplifier may further comprise additional input couplers which are arranged in a way that a signal supplied to the signal input port is divided in more than two output signals, each of which is amplified by a corresponding power amplifier or by a group of power amplifiers connected in parallel, as described above. It may also comprise additional output couplers which are arranged in a way that the resulting amplified signals are then combined to form a transmit signal at the signal output port and to cancel each other at the output isolated port. It has to be made sure that a signal received by the antenna and supplied to the signal output port is sufficiently reflected by the stages before a final combiner so that the reflected components constructively add at the output isolated port to form the receive signal supplied to the receive path.

The radio frequency front end 200 can achieve the same effects as the radio frequency front end 100 shown in Fig. 1. It has the additional effect that no bulky element such as a circulator is required.

In summary, the present invention relates to a radio frequency front end for wireless

communication, especially to a radio frequency front end in which transmitting and receiving is performed using the same antenna and which is suited both for half-duplex operation and for full- duplex operation. The radio frequency front end comprises an antenna port configured to connect an antenna, a transmit path comprising a transmit path output for a transmit signal to be supplied to the antenna port, a receive path comprising a receive path input for a receive signal to be received from the antenna port, a transmit/receive switch connected with a first terminal to the receive path input, and an isolation device connected to the antenna port, the transmit path output, and a second terminal of the transmit/receive switch. The isolation device is configured to isolate the second terminal of the transmit/receive switch from the transmit path output, to supply the transmit signal from the transmit path output to the antenna port, and to supply the receive signal from the antenna port to the second terminal of the transmit/receive switch. While the present invention has been illustrated and described in detail in the drawings and the foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. The invention is not limited to the disclosed embodiments. From reading the present disclosure, other modifications will be apparent to a person skilled in the art. Such modifications may involve other features, which are already known in the art and may be used instead of or in addition to features already described herein.

The invention has been described in conjunction with various embodiments herein. However, other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Although the present invention has been described with reference to specific features and embodiments thereof, it is evident that various modifications and combinations can be made thereto without departing from the spirit and scope of the invention. The specification and drawings are, accordingly, to be regarded simply as an illustration of the invention as defined by the appended claims, and are contemplated to cover any and all modifications, variations, combinations or equivalents that fall within the scope of the present invention.

Claims

1. A radio frequency front end (100) for wireless communication, comprising:

an antenna port (111) configured to connect an antenna (110),

a transmit path (120) comprising a transmit path output (121) for a transmit signal (122) to be supplied to the antenna port (111),

a receive path (130) comprising a receive path input (131) for a receive signal (132) to be received from the antenna port (111),

a transmit/receive switch (140) connected with a first terminal (141) to the receive path input (131), and

an isolation device (150) connected to the antenna port (111), the transmit path output (121), and a second terminal (142) of the transmit/receive switch, and configured to isolate the second terminal (142) of the transmit/receive switch (140) from the transmit path output (141), wherein the isolation device (150) is further configured to supply the transmit signal (122) from the transmit path output (121) to the antenna port (111), and to supply the receive signal (132) from the antenna port (111) to the second terminal (142) of the transmit/receive switch (140).

2. The radio frequency front end (100) according to claim 1, being further adapted

to close the transmit/receive switch (140) when the radio frequency front (100) end is in a full-duplex operation mode or in a half-duplex receive operation mode, and/or

to open the transmit/receive switch (140) when the radio frequency front end (100) is in a half-duplex transmit operation mode.

3. The radio frequency front end (100) according to claim 1 or 2, wherein the isolation device (150) comprises a circulator.

4. The radio frequency front end (200) according to any of claims 1 to 3, wherein the isolation device comprises an output stage of a quadrature balanced amplifier (260) having a transmit signal output port (263) connected to the antenna port (211) and an output isolated port (264) connected to the second terminal (242) of the transmit/receive switch (241).

5. The radio frequency front end (100) according to any of claims 1 to 4, further comprising a signal subtracting device (160) configured to branch-off a first portion (161) of the transmit signal (122),

a filter (170) configured to process the branched-off first portion (161) of the transmit signal, and a signal adding device (180) configured to add the processed branched-off first portion (171) of the transmit signal at the receive path input (131).

6. The radio frequency front end (100) according to claim 5, wherein the filter (170) is a self interference cancellation, SIC, filter configured to process the branched-off first portion (161) of the transmit signal in a way that it causes self interference cancellation with a second portion of the transmit signal that has reached the receive path input (131) via the isolation device (150).

7. The radio frequency front end (100) according to claim 5 or 6, wherein the signal subtracting device (160) comprises a first switching unit (162) that is configured to switch between a first state in which the transmit signal (122) is entirely supplied to the antenna port (111) and a second state in which the first portion (161) of the transmit signal (122) is branched-off towards the filter (170).

8. The radio frequency front end (100) according to any of claims 5 to 7, wherein the signal adding device (180) comprises a second switching unit (182) that is configured to switch between a third state in which the filter (170) is isolated from the receive path input (131) and a fourth state in which the processed branched-off portion (171) of the transmit signal is added at the receive path input (131).

9. The radio frequency front end (100) according to claim 7 or 8, being configured

to switch the first switching unit (162) into the first state and/or the second switching unit (182) into the third state in a half-duplex receive operation mode and/or a half-duplex transmit operation mode, and/or

to switch the first switching unit (162) into the second state and/or the second switching unit (182) into the fourth state in a full-duplex operation mode.

10. The radio frequency front end (100) according to any of claims 1 to 9, wherein an antenna (110) is connected to the antenna port (111).

11. A method for operating a radio frequency front end (130) for wireless communication, the method comprising

supplying a receive signal (132) from an antenna port (111) via an isolation device (150) and a transmit/receive switch (140) to a receive path input (131) of a receive path (130), and/or

supplying a transmit signal (122) from a transmit path output (121) of a transmit path (120) to an antenna port (111) via the isolation device (150) and isolating the transmit/receive switch (140) from the transmit path output (141) by the isolation device (150).

12. The method according to claim 11, further comprising

closing the transmit/receive switch (241) when the radio frequency front (100) end is in a full-duplex operation mode or in a half-duplex receive operation mode, and/or

opening the transmit/receive switch (241) when the radio frequency front end (100) is in a half-duplex transmit operation mode.

13. The method according to claim 11 or 12, further comprising

branching-off (160) a first portion (161) of the transmit signal (122)

processing (170) the branched-off first portion (161) of the transmit signal, and adding (180) the processed branched-off first portion (171) of the transmit signal at the receive path input (131).

14. The method according to claim 13, wherein the branched-off first portion (161) of the transmit signal is processed in a way that it causes self interference cancellation with a second portion of the transmit signal that has reached the receive path input (131).

15. The method according to claim 13 or 14, further comprising

switching into a state in which the transmit signal (122) is entirely supplied to the antenna port (111) and/or no signal is added to the signal at the receive path input (131) in a half-duplex receive operation mode and/or a half-duplex transmit operation mode, and/or

switching into a state in which a portion (161) of the transmit signal (122) is branched-off and/or a processed branched-off portion (171) of the transmit signal is added to the signal at the receive path input (131) in a full-duplex operation mode.