KR102071885B1 - Magnetic-free Balanced In-band Full Duplex RF Front-end using 0°/180° Balancing Power Splitter - Google Patents

Abstract

The present invention relates to an in-band nonmagnetic full duplex communication wireless front end circuit using a balanced and broadband 0°/180° power distributor. More specifically, the in-band nonmagnetic full duplex communication wireless front end circuit comprises a 0°/180° power distributor consisting of a 3-dB Wilkinson power distributor and a pair of 3-dB hybrid combiners. Signals from output terminals of the 0°/180° power distributor are passed through two 3-dB hybrid combiners sequentially connected, and all the signals are radiated to the atmosphere through a specific transmitting antenna. Signals received through specific receiving antennas are only transmitted to receiving terminals, respectively. The signals at the receiving terminal are combined via a 3-dB Wilkinson power combiner and delivered to a receiving unit. The present invention can provide signal isolation features of effectively offsetting a leak signal of a transmitting unit.

Description

Magnetic-free Balanced In-band Full Duplex RF Front-end using 0 ° / 180 ° Balancing Power Splitter}

The present invention relates to an in-band nonmagnetic full-duplex radio front end circuit using a balanced structure and a wideband 0 ° / 180 ° power divider, and more particularly, consisting of a 3-dB Wilkinson power divider and a pair of 3-dB hybrid combiners. 0 ° / 180 ° power divider; including, the signals of the output terminals of the 0 ° / 180 ° power divider passes through two 3-dB hybrid combiner in sequence to radiate all to the atmosphere through a specific transmit antenna, Signals received through specific receive antennas are each delivered only to the receive terminals, and the signals at the receive terminals are combined through a 3-dB Wilkinson power combiner and delivered to the receiver in the same band using a balanced and wideband 0 ° / 180 ° power divider. A non-magnetic full duplex wireless front end circuit is provided.

In general, as high-speed data transmission becomes possible due to the commercialization of LTE mobile communication, an environment for enjoying multimedia contents is provided.

To this end, LTE-A and broadband LTE services have been developed and commercialized to enable faster data rates and high-quality media content. Nevertheless, the network capacity problem due to the increase in the number of users, the increase of data traffic due to the use of various contents, and the lack of frequency resources continue to emerge.

Therefore, in next-generation 5G mobile communication, wider bandwidth is secured to increase network capacity, and traffic distribution and high-speed data transmission are topics. Frequency division duplexing (FDD), as shown in FIG. 1 (a), is a band pass filter using a frequency band independent of a transmission (Tx) and a reception (Rx) band or a channel. Alternatively, the isolation loop can be used to implement transmit and receive signal isolation, but it is difficult to ensure wide frequency bandwidth for transmission and reception. In the time division duplexing (TDD) system as shown in FIG. 1 (b), since data is transmitted and received alternately according to time without separating transmission and reception frequency bands, it is relatively compared to an FDD communication system. It is easy to secure wide frequency bandwidth and will be applied to next generation wireless communication. However, there is a limitation of data transmission time compared to the FDD scheme in which transmission and reception are simultaneously performed all the time, and time synchronization according to a time shift scheme is required between each mobile device and a base station. As shown in FIG. 1C, an in-band full duplexing method simultaneously performs transmission and reception in the same frequency band. Like TDD communication, wide bandwidth can be easily secured by sharing transmission / reception frequency, and it does not require time synchronization and limitation of data transmission time.

However, since the transmission / reception frequency bands are the same, even if a part of the transmission signal having a large signal level is transmitted to the reception unit at the front end of the wireless communication, it causes great interference to the reception signal of a very small signal level that is normally input. Therefore, high signal isolation between the transmitter and the receiver is essential in order not to saturate the receiver's low noise amplifier (LNA) without causing the transmission signal leaked to the receiver to interfere with the normal received signal.

Figure 2 is an example of a conventional co-band full-duplex wireless front end circuit, and unlike the present invention uses a magnetic circulator (circulator). A fixed group delay circuit for forming a signal cancellation path using directional couplers in the RF transceiver, dividing a portion (C) of the transmission signal into several paths and controlling group delay of signals passing through each path. Highly isolated signal transmission and reception by offsetting the transmission signal transmitted to the receiver by adjusting analog attenuators that control delay and signal amplitude, and then combining and applying the analog attenuator circuit to the receiver. Get the characteristics.

Conventionally, the circuit achieves approximately 60 dB signal isolation at the wireless front end using analog cancellation, and adds 50 dB signal isolation at the baseband using a digital microprocessor, resulting in a total of 110 dB signal isolation. Implemented. However, because the analog cancellation circuitry has multiple paths, a 1: n RF signal divider and n: 1 RF signal combiner (Σ), fixed delays and variable delays that allow each path to have different transmission times. Variable attenuators increase the size of the entire wireless front end. In addition, it is difficult to maintain and integrate characteristics at high frequency because a very complicated adjustment algorithm is required to control signals of various paths, and the design complexity is high and magnetic elements such as a circulator are used. .

Conventionally, a circulator and a 3-dB hybrid combiner cancel a transmission signal reflected from an antenna, and a 40-45 dB signal isolation characteristic is obtained by using a cancellation path at a transceiver. However, a dual-feed antenna must be used, and the size of the entire wireless front end becomes large due to the use of multiple circulators and 3-dB hybrid couplers.

As shown in FIG. 3, the transmitter and the receiver are connected to the input and isolation terminals of the ring hybrid, respectively, and the isolation characteristics between the transmission and reception are implemented using the isolation characteristics of the ring hybrid. However, it is difficult to achieve high isolation of 60 dB and large isolation appears only in narrow bands. In addition, half of the transmit power output from the power amplifier (PA) is dissipated at 50Ω termination, resulting in very low transmitter power efficiency.

4 is a block diagram of a co-band full-duplex communication circuit as another example. Unlike other co-band full-duplex circuits, the circuit is composed of two antennas using one transmit (Tx) and one receive (Rx) antenna. Half of the transmitted signal is radiated through the transmit antenna and the other half is used at the receiver to eliminate leakage signals due to the coupling between the transmit (Tx) and receive (Rx) antennas. Therefore, transmitter efficiency cannot exceed 50%.

In addition, broadband isolation characteristics are due to the signal propagation characteristics of the transmit (Tx) -receive (Rx) antenna paths and other propagation characteristics of the offset signals transmitted to the receiver via the balun-attenuator-delay paths. Hard to get.

Therefore, there is a need for a new band full-duplex full-duplex front end to solve these problems.

The co-band full-duplex communication method can simultaneously transmit and receive a transmission and reception signal in the same frequency band, and thus has a frequency efficiency more than twice that of a conventional communication method using a separate transmission and reception frequency.

However, the signal isolation between the transmitter and receiver is very important because the transmission and reception of the radio signal is performed through the same band frequency. For the transmission and reception signal isolation characteristics, high signal isolation characteristics can be obtained by connecting the transmitting and receiving units to isolation terminals of 90 ° hybrid and 180 ° ring hybrids, respectively. not.

In addition, when the transmitter, receiver and antenna are connected to three terminals due to the characteristics of the four-terminal circuit, the other terminal is terminated by 50 Ω. At this time, half of the transmit output power is consumed at the 50 Ω termination, which increases the efficiency of the entire transmitter circuit. It cannot exceed 50%, and it is difficult to obtain wideband signal isolation when forming a cancellation loop using a directional coupler.

In addition, if a circulator (circulator) made of a conventional magnetic material can be relatively easily obtained isolation characteristics, there is a disadvantage that can not deteriorate the isolation characteristics and circuit direct at high frequency.

[1] P. Pirinen, "A brief overview of 5G research activities," 5G for Ubiquitous Connectivity Conf., Pp. 17-22, Nov. 2014. [2] D. Bharadia, E. Mcmilin, and S. Katti, "Full duplex radios," in Proc. ACM SIGCOMM 2013 Conf. on SIGCOMM, pp. 375-386, Oct. 2013. [3] M. E. Knox, "Single antenna full duplex communications using a common carrier," in Proc. 13th Annual Wireless and Microwave Technology Conference (WAMICON), pp. 1-6, Apr. 2012 [4] F. Passerini and A. M. Tonello, "In band full duplex PLC: the role of the hybrid coupler," International Symposium on Power Line Communications and its Applications, May 2016 [5] M. Jain, et al., "Practical, real-time, full duplex wireless," in Proc. 17th Annu. Int. Conf. Mobile Computer Network, pp. 301 ?? 312, Sep. 2011 [6] Q. Wang, H. Kang, S. Jeong, J, Jeong, P. Kim and Y. Jeong. Analysis and design of conventional wideband branch line balun. International Symposium on Information Technology Convergence, pp. 386-389, 2015

The present invention has been made to solve the above problems, and narrowband signal isolation characteristics of the RF front-end of the in-band full duplex proposed in the 5th generation mobile communication system. A new broadband nonmagnetic full duplex wireless front end circuit is proposed to improve the performance

In addition, the present invention implements a physical balance structure with a wideband 0 ° / 180 ° power divider to achieve high signal isolation between the transmitter and receiver over the broadband, effectively preventing the transmitter leakage signal transmitted to the receiver over the broadband frequency. Offset signal isolation can be achieved.

In addition, the present invention can implement the circuit only with a nonmagnetic element to maintain the circuit directing and characteristics even at ultra-high frequency.

In order to solve the above problems, the present invention includes a 0dB / 180 ° power divider consisting of a 3-dB Wilkinson power divider and a pair of 3-dB hybrid combiner, and the signal of the output terminal of the 0 ° / 180 ° power divider. They pass through two 3-dB hybrid combiners sequentially connected and radiate all of the air through a specific transmit antenna into the air, and the signals received through the specific receive antennas are delivered to the receive terminals, respectively, and the signals at the receive terminals are 3-dB Wilkinson power. It is coupled via a combiner and delivered to the receiver.

The 3-dB Wilkinson power divider distributes the transmission signal applied to the transmission input stage into signals of in-phase and of the same amplitude.

The pair of 3-dB hybrid combiners have an open and shorted coupling and transmission stages, respectively, and signals distributed through the 3-dB Wilkinson power divider have the same amplitude while passing through a pair of 3-dB hybrid combiners, but are 180 ° from each other. Are converted into signals having a phase difference of.

Due to the electrical characteristics of the two 3-dB hybrid couplers connected sequentially, the signals of the output terminals of the broadband 0 ° / 180 ° power divider are transmitted only to the transmitting antenna terminal and not to the receiving antenna terminal.

Due to the electrical characteristics of the two sequentially connected 3-dB hybrid combiners, signals received through the receiving antennas are respectively transmitted only to the receiving terminals, and not to the output terminals of the wideband 0 ° / 180 ° power divider.

The present invention as described above improves the narrow-band signal isolation characteristics of the RF front-end in-band full duplex proposed in the fifth generation mobile communication system.

In addition, the present invention implements a physical balance structure with a wideband 0 ° / 180 ° power divider to achieve high signal isolation between the transmitter and receiver over the broadband, effectively preventing the transmitter leakage signal transmitted to the receiver over the broadband frequency. Offset signal isolation can be achieved.

In addition, there is no 3 dB loss of the transmitted signal, which is a problem of the full-duplex radio front end circuit using the conventional 3-dB hybrid combiner or ring hybrid.

In addition, the present invention exhibits good offset characteristics in a wide band around 2.5 GHz through a balanced broadband 0 ° / 180 ° power divider.

1 is a diagram illustrating transmission and reception signal distribution according to a communication method according to the related art (a) frequency division method, (b) time division method, (c) co-band full-duplex method.
2 is a block diagram illustrating a wireless front end part of a conventional full-band full duplex communication system according to the present invention.
3 is a diagram illustrating a co-band full-duplex front end using a ring hybrid according to the related art.
4 is a diagram illustrating a co-band full-duplex front end having an independent transmit / receive antenna according to the related art.
FIG. 5 is a diagram illustrating a co-band nonmagnetic full-duplex wireless front end circuit using a balanced structure and a wideband 0 ° / 180 ° power divider according to the present invention.
6 is a diagram illustrating a leak signal pair and a path in the balanced structure of the present invention.
FIG. 7 shows (a) a balanced broadband 0 ° / 180 ° power divider and (b) a reflective 3-dB hybrid structure.
8 is a diagram illustrating a signal cancellation test diagram of 0 ° / 180 ° power divider circuits.
9 is a diagram illustrating signal cancellation measurement results when a conventional balun, a ring hybrid, and a balanced broadband 0 ° / 180 ° power divider of the present invention are used as the 0 ° / 180 ° power divider of FIG. 8, respectively.
FIG. 10 is a diagram illustrating a co-band nonmagnetic full duplex wireless front end fabricated at 2.5 GHz. FIG.
11 is a diagram illustrating transmission and reception isolation characteristics of a fabrication circuit according to the presence or absence of an antenna.

In order to fully understand the present invention, preferred embodiments of the present invention will be described with reference to the accompanying drawings. Embodiment of the present invention may be modified in various forms, the scope of the invention should not be construed as limited to the embodiments described in detail below. This embodiment is provided to more completely explain the present invention to those skilled in the art. Therefore, the shape of the elements in the drawings and the like may be exaggerated to emphasize a more clear description. It should be noted that the same members in each drawing are sometimes indicated by the same reference numerals. In addition, detailed descriptions of well-known functions and configurations that are determined to unnecessarily obscure the subject matter of the present invention are omitted.

Radio front end of the same-band nonmagnetic full-duplex communication using balanced structure and wideband 0 ° / 180 ° power divider

5 is a diagram illustrating a co-band nonmagnetic full duplex wireless front end circuit using a balanced structure and a wideband 0 ° / 180 ° power divider of the present invention, and FIG. 6 is a diagram illustrating a leakage signal pair and a path in the balanced structure of the present invention. Drawing.

As shown in FIG. 5, the present invention is composed of a co-band nonmagnetic full-duplex wireless front end circuit using a balanced structure and a wideband 0 ° / 180 ° power divider.

At the transmit (Tx) input, a wideband 0 ° / 180 ° power divider was implemented using 3-dB Wilkinson power dividers and 3-dB hybrid combiners.

The transmit signal is applied to the transmit (Tx) input stage and distributed into signals of in-phase and equal amplitude via a 3-dB Wilkinson power divider.

These signals are output to terminals ① and ③ through a reflective 3-dB hybrid coupler, each having a coupled end and a through end shorted and open, respectively. Has a phase difference of °.

At this time, since the two distribution paths are physically symmetrical, the magnitude and group delay of the transmission characteristics according to the frequency become the same.

After that, the signals of the output terminals ① and ③ of the broadband 0 ° / 180 ° power divider pass through two 3-dB hybrid couplers connected in sequence, and finally two transmit antennas Ant. _Tx1 and Ant. All is emitted into the atmosphere via _Tx2 .

At this time, the receiving antenna Ant. _Rx1 and Ant. _{The signals} of the output terminal ① and output terminal ③ of the wideband 0 ° / 180 ° power divider are not transmitted to the _Rx2 terminal.

Therefore, 3 dB loss of the transmission signal, which is a problem of the full-duplex radio front end circuit using the conventional 3-dB hybrid combiner or ring hybrid, does not occur in the circuit according to the present invention.

Receive antenna Ant. _Rx1 and Ant. Signals received through _Rx2 are transmitted to terminal ② and terminal ④, respectively, and not to terminal ① and terminal ③.

The received signals of terminals ② and ④ are combined through a 3-dB Wilkinson power combiner and transmitted to the receiver (Rx).

The circuit according to the present invention has used a balanced structure to achieve high isolation between transmission and reception at broadband.

In the balanced circuit according to the present invention, there are leakage signal pairs leaking from the transmit (Tx) stage to the receive (Rx) stage.

These leakage signal pairs have the same frequency propagation characteristics because they have the same physical transmission path due to the equilibrium structure, and the final reception (Rx) because they have the same amplitude and 180 ° phase difference propagation characteristics over a wide band by a 0 ° / 180 ° power divider. ) Cancel each other out over broadband.

There are three leakage signal pairs in the circuit according to the present invention, and the paths of the offset signal pairs may be represented as shown in FIG. 6.

First, the first pair of leakage signals are the leakage paths ①-② and ③-④ between the input and isolation terminals of the 3-dB hybrid coupler.

The paths of the second leaky signal pair and the third leaky signal pair are ①-Ant. _Tx1 -Ant. _Rx1- ② and ③-Ant. _Tx2 -Ant. _Rx2 -④ and ①-Ant. _Tx1 -Ant. _Rx2 -④ and ③-Ant. _Tx2 -Ant. _Rx1- ②.

Each signal pair and detailed transmission path can be summarized as shown in Table 1 (leak signal pairs and their paths).

Broadband 0 ° / 180 ° Power Divider

7 is a diagram illustrating a reflective 3-dB hybrid structure used for (a) a balanced broadband 0 ° / 180 ° power divider used in the present invention and (b) a balanced broadband 0 ° / 180 ° power divider used in the present invention. FIG. 8 is a diagram illustrating signal cancellation experiments for confirming electrical performance of 0 ° / 180 ° power divider circuits, and FIG. 9 is a conventional balun, ring hybrid, and a balanced broadband 0 ° / 180 of the present invention. This figure shows the result of measuring signal cancellation of power divider.

Since the leakage signal pairs of the balanced circuit according to the present invention can be canceled with each other by the 0 ° / 180 ° power divider of the transmitting end, a broadband 0 ° / 180 ° power divider is required to obtain the transmission and reception isolation characteristics in the broadband. .

Generally, balun and ring hybrid are mainly used to achieve 0 ° / 180 ° power distribution. However, these circuits cannot achieve wideband characteristics because they have 0 ° / 180 ° phase distribution characteristics mainly in narrow frequency bands.

Therefore, the structure according to the present invention implements a broadband 0 ° / 180 ° power divider using a 3-dB Wilkinson power divider and a 3-dB hybrid combiner.

The S-parameters of the reflective 3-dB hybrid shown in FIG. 7 (b) may be expressed by Equation 1 below.

At this time, according to load, transfer characteristic S ₂₁ = -jΓ _L It is determined that Γ _L is represented by Equation 2 according to the open and short conditions.

Since the magnitude of the transfer characteristic is different and the sign differs depending on the load of the open and short circuits, the 0 ° / 180 ° power divider can achieve 0 ° / 180 ° signal distribution in a wide band.

As shown in Fig. 8, the two distributed output signals of the conventional balun and ring hybrid having the 0 ° / 180 ° signal distribution characteristics and the balanced broadband 0 ° / 180 ° power divider of the present invention are combined again into a Wilkinson power combiner. Signal cancelation characteristics were measured.

As shown in FIG. 9, the conventional balun and ring hybrids mainly exhibit good offset characteristics in a specific frequency band, but the balanced broadband 0 ° / 180 ° power divider of the present invention has good offset characteristics in a wide band around 2.5 GHz. It is showing.

Transmission and reception isolation characteristic measurement result

FIG. 10 is a diagram illustrating a non-magnetic full duplex wireless front end of a non-magnetic band manufactured at 2.5 GHz, and FIG. 11 is a diagram illustrating transmission and reception isolation characteristics of a fabrication circuit according to the presence or absence of an antenna.

As shown in FIG. 10, the same band nonmagnetic full duplex wireless front end circuit using a balanced structure implemented at 2.5 GHz and a wideband 0 ° / 180 ° power divider. The measurement was performed using four commercial dipole antennas.

As shown in FIG. 11, when the antenna (antenna port is 50 Ω termination) is measured, only the first pair of the leakage signal pairs shown in Table 1 is present, which shows better characteristics than when the antenna is present.

Based on 60 dB isolation, the absence of an antenna has a bandwidth of 190 MHz (2.37 to 2.56 GHz).

In the case of measurement using an antenna, the characteristics are relatively degraded since all leakage signal pairs shown in Table 1 exist and each cancels at the receiving end. The measured 60 dB isolation bandwidth is 113 MHz (2.446 to 2.559 GHz).

10: 0 ° / 180 ° power divider
12: 3-dB Wilkinson Power Splitter
14, 16: 3-dB hybrid combiner
18-1, 18-2: receiving antenna
18-3, 18-4: transmitting antenna
20: 3-dB hybrid combiner
30: 3-dB Wilkinson Power Combiner

Claims (5)

In the same band nonmagnetic full duplex wireless front end circuit using a balanced structure and a wideband 0 ° / 180 ° power divider,
0 ° / 180 ° power divider 10 consisting of a 3-dB Wilkinson power divider 12 and a pair of 3-dB hybrid combiners 14 and 16;
Signals of the output terminals of the 0 ° / 180 ° power divider 10 are respectively passed through two 3-dB hybrid combiners 20 sequentially connected to the air through specific transmit antennas 18-3 and 18-4. Radiate all, and the signals received through the specific receiving antennas 18-1 and 18-2 are transmitted to the receiving terminals, respectively, combined through the 3-dB Wilkinson power combiner 30, and transmitted to the receiving unit Rx. A non-magnetic full-duplex radio front end circuit using a balanced structure and a wideband 0 ° / 180 ° power divider. The method of claim 1,
The 3-dB Wilkinson power divider distributes a transmission signal applied to a transmission (Tx) input stage into signals of the same phase and the same amplitude, and the same band using a wideband 0 ° / 180 ° power divider. Nonmagnetic full duplex wireless front end circuit. The method of claim 2,
The 3-dB hybrid combiner has an equilibrium structure and a wideband bandwidth, wherein the coupler and the through end are respectively opened and shorted, and the divided signals have the same amplitude but phase differences of 180 ° from each other. Coband nonmagnetic full duplex wireless front end circuit using 0 ° / 180 ° power divider. The method of claim 1,
Due to the electrical characteristics of the two 3-dB hybrid couplers 20 sequentially connected, signals of the output terminals of the broadband 0 ° / 180 ° power divider are not transmitted to the terminals of the reception antennas 18-1 and 18-2. A coband nonmagnetic full-duplex wireless front end circuit using a balanced structure and a wideband 0 ° / 180 ° power divider, characterized in that. The method of claim 1,
The signals received through the receiving antennas 18-1 and 18-2 are respectively transmitted to the receiving terminals by the electrical characteristics of the two 3-dB hybrid couplers connected sequentially, and the broadband 0 ° / 180 ° power divider output terminals are provided. A non-magnetic full-duplex wireless front end circuit using a balanced structure and a wideband 0 ° / 180 ° power divider, characterized in that it is not transmitted to the furnace.

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