Duplexer

Abstract

A duplexer (1), comprising - an antenna connection (2), - a transmit port (3), and - a receiving connection (4), wherein a first bandpass filter (6) is arranged between the transmit terminal (3) and the antenna terminal (2), wherein a directional line (9) is arranged between the first bandpass filter (6) and the antenna connection (2), wherein the directional line (9) is arranged directly at the antenna connection (2) and has a tunable frequency characteristic which can be tuned to different pass frequencies.

Description

[0001] The present invention relates to a duplexer. The duplexer can comprise exclusively BAW filters (Bulk Acoustic Wave Filters) or a combination of BAW filters and SAW filters (Surface Acoustic Wave Filters). Furthermore, duplexers comprising exclusively SAW filters are also possible. Duplexers implemented using a different technology, such as stripline, waveguide, or dielectric duplexers, are also possible.

[0002] Duplexers can exhibit pronounced nonlinear behavior. The term nonlinearity refers to the occurrence or emergence of interfering frequency components generated by filter structures that are not completely linear. Nonlinearities can arise, in particular, from the superposition of transmitted signals and interference signals.

[0003] A variety of approaches to reducing nonlinearities in duplexer circuits are known in the prior art. Examples include modifying the finger geometry of the filters used or using diversity duplexers. Such a circuit arrangement is disclosed, for example, in DE 10 2011 018918 A1. However, these approaches do not lead to the desired suppression of the interference signal when the frequency is very similar to the frequency of the transmitted signal.

[0004] Furthermore, US 2009 / 0 040 109 A1 discloses a transceiver circuit in which an antenna is directly connected to a duplexer. In the transmit branch of this circuit, an isolator is also connected to the duplexer.

[0005] Document US 5,659,886 A discloses a digital mobile radio device in which a duplexer for connecting a transmitter and a receiver to a common receive / transmit antenna is constructed from an isolator and a receive bandpass filter. The receive bandpass filter prevents a transmitted wave from entering the receiver. The impedance matching is performed such that the isolator can prevent a received wave from entering the transmitter while suppressing the entry of signals radiated by other mobile units in the same transmission frequency band but at a different operating frequency.

[0006] Document DE 10 2004 039 674 A1 discloses a relaying base station comprising an antenna, a duplexer, a first and a second transmission branch, and a first and a second reception branch. The duplexer includes a first and a second transmission / reception filter, each tunable to a first and a second carrier frequency range of the FDD radio signal transmission. The antenna is connected to the first transmission branch via the first transmission / reception filter at a first time and to the first reception branch at a second time.

[0007] Document EP 1 487 121 A1 discloses an isolator circuit for an antenna system comprising a tunable isolator; a detector for detecting a reflected signal; and a tuner for tuning the center frequency of the isolator in response to the reflected signal to reduce the power consumption of the isolator circuit.

[0008] Document US 2011 / 0 279 194 A1 discloses a duplexer module that includes a transmit line, a receive line, and a common antenna line, and performs conversion between a transmit signal and a receive signal and common antenna signals. A transmit filter is inserted into the transmit line, which passes the transmit signal and stops the receive signal. A receive filter is inserted into the receive line, and the receive filter passes the receive signal and stops the transmit signal. A first line of a coupler, which detects the transmit signal, is inserted into the transmit line in a stage after the transmit filter.

[0009] Document US 2013 / 0 070 749 A1 discloses a device for separating signal transmission and reception, comprising first, second, and third device terminals. The device further comprises a circulator having first, second, and third circulator terminals, a transmission filter connected between the first circulator terminal and the first device terminal, and a reception filter connected between the third circulator terminal and the third device terminal. The second circulator terminal is coupled to the second device terminal. An input to the first terminal is output from the second terminal, and an input to the second terminal is output from the third terminal. The circuit provides isolation between transmission and reception to improve communication efficiency and can reduce the size of a communication system.

[0010] It is an object of the present invention to provide a duplexer having improved linearity.

[0011] This object is achieved by a duplexer according to claim 1.

[0012] A duplexer is proposed which has an antenna connection, a transmit connection and a receive connection, wherein a first bandpass filter is arranged between the transmit connection and the antenna connection, and wherein a directional line is arranged between the first bandpass filter and the antenna connection.

[0013] A directional line is also called an isolator. A directional line can also be referred to as a "one-way line." A directional line is characterized by a preferred forward direction. It exhibits lower insertion loss for signals traveling through it in the direction of the preferred forward direction than for signals traveling in a direction opposite to the preferred forward direction.

[0014] The duplexer therefore has the transmit port, the first bandpass filter, the directional line, and the antenna port, which are connected to each other in this order. The antenna port is suitable for connecting the duplexer to an antenna.

[0015] The arrangement of the directional line between the transmit connection and the antenna connection makes it possible to suppress interference signals received from the antenna connection and directed to the transmit connection, thus avoiding or at least significantly suppressing the occurrence of non-linearities.

[0016] Another advantage of locating the directional line between the transmit port and the antenna port is that it allows for a very compact duplexer with a small footprint. The directional line, along with the duplexer's filters, can be combined into a single component, which can be housed in a single housing.

[0017] Furthermore, the arrangement of the directional line in the immediate vicinity of the antenna connection ensures that interference signals coupled via the antenna connection are suppressed at an early stage, thus avoiding the occurrence of non-linearities.

[0018] In general, the duplexer is advantageous for applications in which two signals are generated and / or processed whose frequencies are identical or similar to each other. The duplexer is particularly advantageous for applications in which two signals are generated and / or processed whose frequencies lie within the passband of a filter and / or whose mixing products lie within the passband of a filter. Examples of this include mobile radio in portable mobile phones, small cell applications, or applications in the field of radar technology.

[0019] The receive port of the duplexer can be single-ended or balanced.

[0020] Furthermore, the directional line can be arranged such that signals passing through the directional line in the direction from the transmitting connection to the antenna connection are attenuated less than signals passing through the directional line in the opposite direction.

[0021] The signals passing through the directional line from the transmit port to the antenna port are typically transmit signals coupled to the transmit port by a transmit-receive circuit. Accordingly, the signal strength of these signals should be reduced as little as possible. The directional line can be arranged so that the preferred direction of travel of the directional line points from the transmit port to the antenna port. This ensures that the transmit signals experience only minimal attenuation by the directional line.

[0022] The signals that pass through the directional line in the direction from the antenna connection to the transmit connection are typically interference signals that are coupled at the antenna connection. Accordingly, the signal strength of these signals should be reduced as much as possible to avoid or at least reduce the occurrence of nonlinearities. If the directional line is arranged, as described above, so that the preferred direction of transmission of the directional line points from the transmit connection to the antenna connection, the interference signals that run opposite to the preferred direction of transmission are significantly attenuated by the directional line.

[0023] Furthermore, the directional line can have an insertion loss of a maximum of 1.0 dB, which affects signals passing through the directional line in the direction from the transmit port to the antenna port. In particular, the directional line can have an insertion loss between 0.2 dB and 1.0 dB, which affects signals passing through the directional line in the direction from the transmit port to the antenna port.

[0024] Furthermore, the directional line can have an insertion loss of at least 5 dB, which acts on signals passing through the directional line in the direction from the antenna connection to the transmit connection. In particular, the directional line can have an insertion loss of between 8 dB and 25 dB, which acts on signals passing through the directional line in the direction from the antenna connection to the transmit connection.

[0025] The numerical ranges given here make it clear that the directional line can be designed in such a way that signals passing through the directional line in the direction from the transmit connection to the antenna connection experience a significantly lower insertion loss than signals passing through the directional line in the direction from the antenna connection to the transmit connection.

[0026] The insertion loss value ranges specified here refer to signals whose frequencies lie within the frequency bands specified in the mobile communications standards, in particular in the LTE frequency bands.

[0027] In one embodiment, the first bandpass filter may have a tunable passband. Accordingly, the passband of the first bandpass filter can be adjusted to different frequencies. In this way, the duplexer can be used for transmitting and / or receiving data in different frequency ranges.

[0028] The directional line also has a passband, whereby it attenuates signals whose frequencies lie within this passband less than signals whose frequencies lie outside the passband. The passband of the directional line can be wider than the passband of the first bandpass filter. If the first bandpass filter has a tunable passband and the passband of the directional line is not tunable, the tunable passband of the first bandpass filter can be limited so that the tunable passband of the first bandpass filter can only be set to frequencies that lie within the passband of the directional line.

[0029] Furthermore, the directional line can have a tunable frequency characteristic that can be adjusted to different passband frequencies. This allows the passband of the directional line to be tuned. Accordingly, the duplexer can be used for a wider frequency range. In this case, the bandwidth of the directional line no longer acts as a limiting factor.

[0030] In particular, the combination of a first bandpass filter whose pass frequency is tunable with a directional line whose pass frequency is tunable results in a duplexer that can be used over a very wide frequency range.

[0031] Furthermore, a second bandpass filter and a first phase shifter can be arranged between the receiving terminal and the antenna terminal.

[0032] The second bandpass filter can also have a tunable passband. The second bandpass filter is connected to the receive port. If the second bandpass filter has a tunable passband, the duplexer can be tuned to receive signals from different frequency bands.

[0033] Furthermore, a second phase shifter can be arranged between the directional line and the antenna connection.

[0034] The first and second phase shifters can have frequency characteristics that can be tuned to different pass frequencies. This feature also allows the duplexer to be better adapted for use in different frequency bands.

[0035] According to a further aspect, the present invention relates to a circuit arrangement comprising a first duplexer and a second duplexer, wherein the first and second duplexers are each a duplexer in which a first bandpass filter and a directional line are arranged between a transmit connection and an antenna connection. Thus, the first and second duplexers can each be one of the duplexers described above. In particular, the first and second duplexers can have any structural and functional feature disclosed herein in connection with the duplexer according to claim 1 and the corresponding embodiments of this duplexer.

[0036] Furthermore, in the circuit arrangement, a first antenna can be connected to the antenna terminal of the first duplexer and a second antenna can be connected to the antenna terminal of the second duplexer.

[0037] Accordingly, the circuit arrangement is particularly suitable for use in mobile communications standards, where signals are transmitted and / or received simultaneously via two antennas. If frequencies from the same frequency band are used, the duplexers enable the commonly occurring nonlinearities to be significantly attenuated. The directional conduction in each duplexer allows the transmitter's own transmission signal to pass through the duplexer virtually unattenuated, significantly attenuating any interference signal coming from the respective antenna connection.

[0038] The SV-LTE (Simultaneous Voice LTE) standard is a mobile communications standard in which signals are transmitted and / or received simultaneously via two antennas. SVDO (Simultaneous Voice Data Optimized) systems also transmit and / or receive signals simultaneously via two antennas. Accordingly, the circuit arrangement described above offers advantages, particularly for these systems. However, it can also be used to improve linearity when using other transmission standards.

[0039] The invention is explained in more detail below using exemplary embodiments and the associated figures. The figures show various exemplary embodiments of the invention using schematic representations that are not to scale. Fig. 1 shows a duplexer. Fig. 2 also shows the Fig. 1, where the power level curve for two different signals in the duplexer is indicated. Fig. 3 shows a circuit arrangement having two duplexers. Fig. 4 shows a second embodiment of the duplexer. Fig. 5 shows a third embodiment of the duplexer. Fig. 6 shows a fourth embodiment of the duplexer. Fig. 7 shows a fifth embodiment of the duplexer. Fig. 8 shows a sixth embodiment of the duplexer. Fig. 9 shows a seventh embodiment of the duplexer.

[0040] Fig. Figure 1 shows a duplexer 1 according to the invention. The duplexer 1 has an antenna port 2, a transmit port 3, and a receive port 4. The transmit port 3 is connected to the antenna port 2 via a transmit path 10. The receive port 4 is connected to the antenna port via a receive path 11.

[0041] Fig. Figure 1 further shows that the antenna port 2 is connected to an antenna 5. Furthermore, the transmit port 3 and the receive port 4 can be connected to a transmit-receive circuit (not shown). The duplexer 1 is particularly suitable for use in a mobile terminal, where it is connected to an antenna 5, via which signals are simultaneously received and transmitted. These signals are, for example, signals whose frequencies lie within the frequency bands specified by the mobile communications standards, in particular within the LTE frequency bands.

[0042] The Fig. The duplexer 1 shown in Figure 1 has a first bandpass filter 6 and a second bandpass filter 7. The first bandpass filter 6 is arranged between the transmit port 3 and the antenna port 2. The second bandpass filter 7 is arranged between the receive port 4 and the antenna port 2.

[0043] Furthermore, the duplexer 1 has a first phase shifter 8. The first phase shifter 8 is arranged between the second bandpass filter 7 and the antenna connection 2.

[0044] Furthermore, the duplexer 1 has a directional line 9. The directional line 9 is arranged between the first bandpass filter 6 and the antenna connector 2. The directional line 9 is characterized by a preferred forward direction. It has a lower insertion loss for signals passing through it in the direction of the preferred forward direction than for signals passing through it in a direction opposite to the preferred forward direction.

[0045] The directional line 9 is arranged such that its preferred transmission direction runs from the transmission port 3 to the antenna port 2. Accordingly, transmission signals fed into the transmission port 3 of the duplexer 1 are only slightly attenuated in the directional line 9 and therefore reach the antenna 5 almost unattenuated. Conversely, interference signals received by the antenna 5 and entering the transmission path 10 in the direction of the transmission port 3 are attenuated more strongly by the directional line 9.

[0046] For example, in its preferred forward direction, the directional line 9 has an insertion loss of between 0.2 and 1.0 dB. Preferably, it has an insertion loss of 0.5 to 0.7 dB. In the direction opposite to the preferred forward direction, the directional line has an insertion loss of 5 to 50 dB, preferably 8 to 25 dB. These specifications refer to signals whose frequencies lie in one of the bands of the LTE mobile communications standard. In particular, these specifications refer to signals whose frequencies lie in band 2 of the LTE standard.

[0047] Fig. 2 explains the functionality of the Fig. 1, where the power level curve for two different signals in the duplexer 1 is given using an example calculation. The respective frequency f1 or f2 of the two signals lies in the passband of the first bandpass filter 6.

[0048] A first signal is applied to the transmit port 3 as a transmit signal with a frequency f1 and a signal strength of 26.6 dBm. The frequency f1 is within the passband range of the first bandpass filter 6. In the first bandpass filter 6, this signal is attenuated by 2 dB, so that it has a signal strength of 24.6 dBm between the first bandpass filter 6 and the directional line 9. The transmit signal passes through the directional line 9 in the preferred pass direction and is accordingly attenuated by 0.6 dB. The signal thus has a signal strength of 24 dBm when it reaches the antenna 5.

[0049] Furthermore, a second signal is received by antenna 5 as an interference signal with frequency f2 and a signal strength of 14 dBm. It is further assumed here that frequency f2 lies in the same frequency band as frequency f1 of the first signal and is thus within the passband of the first bandpass filter 6. The second signal passes through the directional line 9 opposite to the preferred passband direction and is accordingly attenuated by 10 dB. Furthermore, the second signal is attenuated by a further 2 dB in the first bandpass filter 6. Accordingly, when it reaches the transmitting port 3, it only has a signal strength of 2 dBm.

[0050] Fig. Figure 2 thus clearly shows that the arrangement of the directional line 9 proposed here enables the effective suppression of interference signals coupled into the antenna connection 2. In particular, the directional line 9 also enables significant attenuation of interference signals that lie in the frequency band of the transmission signal. This also significantly reduces nonlinearities in the duplexer 1, which result from mixed terms of these interference signals and the transmission signals, since the power of the interference signals is significantly attenuated.

[0051] Fig. 3 further shows a circuit arrangement 12 in which two of the Fig. 1 are connected to a transmit / receive circuit 13. The transmit / receive circuit 13 has amplifiers 15, 16, each of the amplifiers 15, 16 being connected to the transmit connection 3 of the respective duplexer 1. In each of the two duplexers 1, a directional line 9 is arranged between the respective first bandpass filter 6 and the respective antenna connection 2 such that the preferred forward direction of the directional line 9 runs from the first bandpass filter 6 to the antenna connection 2.

[0052] Furthermore, the antenna port 2 of one of the two duplexers 1 is connected to a first antenna 5. The antenna port 2 of the other of the two duplexers 1 is connected to a second antenna 14.

[0053] The circuit arrangement 12 is suitable, for example, for use in data transmission in SV-LTE (Simultaneous Voice-LTE) mode. The circuit arrangement 12 allows data to be transmitted via the first antenna 5 and a call to be conducted via the second antenna 14 simultaneously. Frequencies from a single frequency band, for example, LTE band 2, can be used for both data transmission via the first antenna 5 and signal transmission via the second antenna 14.

[0054] In this case, the signals emitted by the first antenna 5 are coupled into the second antenna 14 as interference signals. Conversely, the signals emitted by the second antenna 14 are coupled into the first antenna 5 as interference signals. A particular problem is that this configuration can lead to non-linear behavior of the circuit arrangement 12 if mixed products arise from the interference signals and the transmitted signals and the frequency of these mixed products lies in the frequency band of the respective received signal.

[0055] However, the duplexer 1 ensures good decoupling of the interference signals coupled from one antenna 5, 14 to the other antenna 14, 5. This significantly suppresses the occurrence of mixing terms described above, which could cause nonlinear behavior. The circuit arrangement 12 therefore makes it possible to significantly suppress the nonlinear behavior that can occur when operating two antennas 5, 14 in the same frequency band.

[0056] By using the directional line 9 in the transmit branch of the duplexer 1, the interference power can be reduced by about 10 dB before it reaches the first bandpass filter 6.

[0057] The advantages described here in connection with SV-LTE can also be exploited with SVDO (Simultaneous Voice Data Optimized) systems. These systems also allow simultaneous conversations and independent data transmission, using frequencies from the same frequency band for both.

[0058] As discussed above, duplexer 1 is particularly advantageous in configurations where two frequencies from a single transmission frequency band can be combined, so that their mixing products lie in the reception frequency band belonging to this transmission frequency band. However, the arrangement of directional line 9 in the transmission path also results in improved suppression of interference signals in other configurations.

[0059] Fig. 4 shows a second embodiment of the duplexer 1. In the Fig. In the duplexer 1 shown in Figure 4, the receiving port 4 is balanced. Fig. In the duplexer 1 shown in Figure 1, the receive port 4 is single-ended. Otherwise, the two duplexers 1 are identical.

[0060] Fig. 5 shows a third embodiment of the duplexer 1. The duplexer 1 according to the third embodiment differs from that shown in Fig. 1 in that it has a second phase shifter 17. The second phase shifter 17 is arranged in the transmission path 10. The second phase shifter 17 is arranged between the directional line 9 and the antenna connection 2. In the duplexer 1 shown in Fig. In the duplexer 1 shown in Figure 5, the receiving port 4 is single-ended.

[0061] In a fourth embodiment, the receiving terminal 4 can be balanced. The fourth embodiment is shown in Fig. 6 shown.

[0062] Fig. 7 shows a fifth embodiment of duplexer 1. Duplexer 1 according to the fifth embodiment differs from duplexer 1 according to the third embodiment in that the first bandpass filter 6 and the second bandpass filter 7 are each tunable in their respective passbands. This allows duplexer 1 to be set to different frequency ranges, making it suitable for transmitting and receiving signals from these frequency ranges. The tunable passbands of the first and second bandpass filters 6, 7 increase the bandwidth in which duplexer 1 can be used. However, this bandwidth is limited by a passband of directional line 9.

[0063] Fig. Figure 8 shows a sixth embodiment of duplexer 1, in which the passband of directional line 9 is also tunable. In particular, the frequency characteristic of directional line 9 can be tuned. Thus, the bandwidth of duplexer 1 is no longer limited by the passband of directional line 9.

[0064] Fig. Figure 9 shows a seventh embodiment of the duplexer 1, in which the first and second phase shifters 8, 17 are also tunable. In particular, the frequency characteristics of the first and second phase shifters 8, 17 can be tuned so that the phase shifters 8, 17 can also be optimized for the respective frequency band.

[0065] Fig. 7, Fig. 8 and Fig. 9 each show the receiving port 4 in a single-ended configuration. However, in alternative configurations, this can also be configured as a balanced port.

[0066] For those in Fig. 3, any two duplexers 1 according to one of the first to seventh embodiments can be combined with each other. Reference symbol 1 duplexer 2 antenna connections 3 Transmission connection 4 Reception connection 5 (first) antenna 6 first bandpass filter 7 second bandpass filter 8 first phase shifter 9 Directional line 10 Send path 11 Reception path 12 Circuit arrangement 13 Transceiver circuit 14 second antenna 15 amplifiers 16 amplifiers 17 second phase shifter

Claims

[1] A duplexer (1), comprising - an antenna connection (2), - a transmission connection (3), and - a receiving connection (4), wherein a first bandpass filter (6) is arranged between the transmitting connection (3) and the antenna connection (2), wherein a directional line (9) is arranged between the first bandpass filter (6) and the antenna connection (2), wherein the directional line (9) is arranged directly at the antenna connection (2) and has a tunable frequency characteristic which can be tuned to different pass frequencies. [2] Duplexer (1) according to claim 1, wherein the directional line (9) is arranged such that signals passing through the directional line (9) in the direction from the transmitting connection (3) to the antenna connection (2) are attenuated to a lesser extent than signals passing through the directional line (9) in the opposite direction. [3] Duplexer (1) according to one of the preceding claims, wherein the directional line (9) has an insertion loss of maximum 1.0 dB acting on signals passing through the directional line (9) in the direction from the transmitting port (3) to the antenna port (2). [4] Duplexer (1) according to one of the preceding claims, wherein the directional line (9) has an insertion loss between 0.2 dB and 1.0 dB acting on signals passing through the directional line (9) in the direction from the transmitting port (3) to the antenna port (2). [5] Duplexer (1) according to one of the preceding claims, wherein the directional line (9) has an insertion loss of at least 5 dB acting on signals passing through the directional line (9) in the direction from the antenna terminal (2) to the transmit terminal (3). [6] Duplexer (1) according to one of the preceding claims, wherein the directional line (9) has an insertion loss between 8 dB and 25 dB acting on signals passing through the directional line (9) in the direction from the antenna terminal (2) to the transmit terminal (3). [7] Duplexer (1) according to one of the preceding claims, wherein the first bandpass filter (6) has a tunable passband. [8] Duplexer (1) according to one of the preceding claims, wherein a second bandpass filter (7) and a first phase shifter (8) are arranged between the receiving terminal (4) and the antenna terminal (2). [9] Duplexer (1) according to claim 8, wherein the second bandpass filter (7) has a tunable passband. [10] Duplexer (1) according to claim 8, wherein the first phase shifter (8) has a tunable frequency characteristic that can be tuned to different pass frequencies. [11] Circuit arrangement comprising a first duplexer (1) according to one of the preceding claims and a second duplexer (1) according to one of the preceding claims. [12] Circuit arrangement according to claim 11, wherein a first antenna (5) is connected to the antenna terminal (2) of the first duplexer (1) and a second antenna (14) is connected to the antenna terminal (2) of the second duplexer (1).

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