RF circuit and front-end circuit with RF circuit

Abstract

RF circuit (HF-S) for Tx Carrier Aggregation, comprising - a diplexer (DI) with a first port (P1), a common port (PG) and a second port (P2), - a first duplexer (DU-HB-1) for a first frequency band with a transmit port (TX), a common port (PG) and a receive port (RX), - a first duplexer (DU-LB-1) for a second frequency band with a transmit port (TX), a common port (PG) and a receive port (RX), wherein the first frequency band is the 2 GHz band or the 2.5 GHz band and the second frequency band is the 1 GHz band, - a first signal path (SP1) between the common port (PG) of the first duplexer (DU-HB-1) of the first frequency band and the first port (P1) of the diplexer (DI), wherein the first signal path (SP1) connects the common port (PG) of the first duplexer (DU-HB-1) of the first frequency band to the first port (P1) of the diplexer (DI), - a second signal path (SP2) between the common port (PG) of the first duplexer (DU-LB-1) of the second frequency band and the second port (P2) of the diplexer (DI), - in the second signal path (SP2) a phase shifter (PS) which is designed to match the impedances of the first duplexer (DU-LB-1) of the second frequency band and the diplexer (DI) for at least one harmonic of one of the frequency bands in such a way that at least one intermodulation product is reduced, wherein the phase shifter (PS) is tunable in its phase offset.

Description

[0001] The invention relates to RF circuits that can be used, for example, in front-end circuits of mobile radio devices.

[0002] Front-end circuits of mobile devices connect one or more receive or transmit amplifiers to one or more antennas. This connection is made via signal paths and RF filters, which are interconnected in such a way that the signal quality requirements of the mobile devices are met while simultaneously allowing the use of a variety of transmission systems and frequencies.

[0003] RF circuits with a tunable duplexer are known from patent US 7,212,789 B2.

[0004] Multiband reception circuits with reduced interference in the reception path by coupling with another signal path are known from US 2003 / 0125001.

[0005] Front-end circuits with phase shifters as signal dividers are known from US 2007 / 0173210 A1.

[0006] Diplexers with metallized structures between dielectric layers are known from US 2005 / 0146398 A1.

[0007] Multiband multi-antenna systems are known from US 2014 / 0328220 A1.

[0008] A miniaturized and power-saving antenna duplexer is known from US 2005 / 0206478 A1.

[0009] While conventional FSS systems (FDD = frequency division duplexing) already use transmit and receive frequencies simultaneously, to increase the data transmission rate, different transmit frequencies or different receive frequencies can be used simultaneously (carrier aggregation). In interband carrier aggregation systems, two FDD receive frequencies can be used simultaneously with one FDD transmit frequency. It is also possible for two FDD transmit frequencies to be used simultaneously with one or more receive frequencies (Tx carrier aggregation).

[0010] However, such joint use of different frequency bands will cause problems with conventional RF circuits, as these are not adapted to the additional RF power, particularly with regard to the separation of different signal paths.

[0011] The objective is therefore to provide an RF circuit that enables good separation between different signal paths, even when exposed to RF signals from different frequency bands. In particular, interference with a signal path due to intermodulation products should be reduced.

[0012] This object is achieved by the RF circuit according to claim 1. Dependent claims specify advantageous embodiments.

[0013] For this purpose, an RF circuit comprises a diplexer, a first duplexer for a first frequency band, and a first duplexer for a second frequency band. The diplexer has a first port, a common port, and a second port. The first duplexer for the first frequency band has a transmit port, a common port, and a receive port. The first duplexer for the second frequency band also has a transmit port, a common port, and a receive port. The circuit further comprises a first signal path between the common port of the first duplexer of the first frequency band and the first port of the diplexer. The RF circuit further comprises a second signal path between the common port of the first duplexer, the second frequency band, and the second port of the diplexer. The circuit also comprises a phase shifter arranged in the second signal path.The phase shifter is provided to adapt the impedances of the first duplexer of the second frequency band and of the diplexer for at least one harmonic of one of the frequency bands such that at least one intermodulation product is reduced.

[0014] The impedance matching particularly concerns the impedance of the common port of the first duplexer of the second signal path and the second port of the diplexer.

[0015] The harmonic can in particular be the second or third harmonic of transmission frequencies, e.g. of the first frequency band.

[0016] The improved signal separation of such an RF circuit is therefore due to the reduction of intermodulation products. It has been recognized that in conventional RF circuits of front-end circuits, the isolation of a diplexer used can be so poor that unwanted RF signals entering a signal path can cause intermodulation products due to nonlinear effects in a duplexer connected downstream of the diplexer. Their frequencies lie within the passband of the duplexer. Such unwanted RF signals cannot be further eliminated by conventional RF filters because their frequencies are similar to the frequencies of desired signals.

[0017] The phase shifter efficiently prevents the formation of these intermodulation products or at least attenuates them to such an extent that the unwanted but significantly weaker intermodulation products no longer cause any further interference.

[0018] This RF circuit is compatible with common circuit topologies of front-end circuits, whereby the comparatively large gain in signal quality is offset by a comparatively small additional circuit effort.

[0019] It is possible that the diplexer is a ceramic diplexer.

[0020] Such a ceramic diplexer can comprise a base body made of an insulating material, e.g., ceramic. Recesses whose inner surfaces are covered with metallization can be provided in the base body. Such a diplexer typically already exhibits very high linearity.

[0021] It is possible for the first frequency band to be the 2 GHz band, and the second frequency band to be the 1 GHz band. The first frequency band then essentially comprises the frequencies between 1 GHz and 2 GHz, in particular between 1.4 and 2.2 GHz. The second frequency band then essentially comprises frequencies ≤ 1 GHz.

[0022] It is also possible that the first frequency band and the second frequency band are selected from the three frequency ranges: Low Band (LB, approx. 650 to 1000 MHz), Mid Band (MB, 1700 - 2200 MHz) and High Band (HB, frequencies f essentially > 2500 MHz).

[0023] In particular, the mobile radio frequency bands 1, 2, 3, 4, 5, 7, 8, 12, 17, 19, 20, 21, 26, or 28 can be considered as the first or second frequency band, e.g., for carrier aggregation of transmission frequencies. Mobile radio bands 5, 8, 12, 17, 19, 20, 26, and 28 are assigned to the LB. Mobile radio bands 1, 2, 3, 4, and 21 are assigned to the MB, and frequency band 7 is assigned to the HB.

[0024] For example, the following frequency band pairs can be used together: LB and LB: 5 and 12, 5 and 17; LB and MB: 3 and 5, 1 and 5, 3 and 20, 1 and 19, 3 and 8, 4 and 12, 4 and 17, 3 and 26, 3 and 19, 19 and 21; MB and MB: 1 and 21, 2 and 4; MB and HB: 1 and 7, 3 and 7, 4 and 7; LB and HB: 7 and 20, 7 and 28, 5 and 7.

[0025] It is also possible for the RF circuit to further comprise a second or several additional duplexers of the first frequency band. The second duplexer or the several additional duplexers of the first frequency band can be connected in parallel to the first duplexer of the first frequency band on the one hand and to the first signal path on the other. This allows transmission operation—whether simultaneously or sequentially—via different duplexers of the first frequency band.

[0026] It is also possible for the RF circuit to include a switch arrangement, via which the first port of the diplexer can be connected to the second or several other duplexers of the first frequency band. The switch arrangement can be used to individually set which duplexer should be connected to the diplexer. It is possible for exactly one duplexer to be connected to the diplexer at any given time. However, it is also possible for no duplexer at all or for several duplexers to be connected to the diplexer at the same time.

[0027] Furthermore, it is possible for the RF circuit to comprise a second or more additional duplexers of the second frequency band. The second or more additional duplexers of the second frequency band can be connected in parallel to the first duplexer of the second frequency band, on the one hand, and to the second signal path, on the other hand.

[0028] It is also possible for the RF circuit to further comprise a further switch arrangement via which the second port of the diplexer can be connected to one or more of the duplexers of the second frequency band.

[0029] Analogous to the above-mentioned situation of the first frequency band, the number of duplexers of the second frequency band that are connected to the diplexer can also be set individually.

[0030] It is possible for the phase shifter to be tunable. A tunable phase shifter can be understood, in particular, as a phase shifter whose characteristic frequencies and / or phase offset for relevant frequencies can be adjusted.

[0031] It is possible that one phase shifter is provided in the second signal path for each duplexer of the second frequency band.

[0032] If the RF circuit includes multiple phase shifters, these can be selected from any of the alternatives listed above. However, it is also possible for several or all phase shifters to be of the same type.

[0033] The phase shifter can reflect an unwanted signal coming from the diplexer back to the diplexer. Desired signals in the corresponding frequency range can pass through the diplexer without significant power loss. The phase shifter can, in particular, be a tunable phase shifter, in which the degree of phase shift of a signal at a specific frequency can be adjusted. For example, the phase shift caused by the phase shifter preferably varies linearly with the frequency of the applied signal.

[0034] A phase shifter designed as a phase shifter can in particular be an all-pass filter consisting of inductances and capacitances.

[0035] It is also possible to use a stripline as a phase shifter.

[0036] In particular, it is possible for the RF circuit to be integrated into a mobile radio device, e.g., in a front-end circuit of the mobile radio device. A mobile radio device whose front-end circuit includes such an RF circuit provides the user with an increased data rate while simultaneously maintaining signal quality.

[0037] The number of duplexers per first or second frequency band is not limited. Both the first and second frequency bands can independently have 1, 2, 3, 4, or more duplexers.

[0038] The first frequency band can have 1, 2, 3, 4, 5, or more duplexers. The second frequency band can also have 1, 2, 3, 4, 5, or more duplexers.

[0039] In the following, central principles of the RF circuit and some non-exhaustive embodiments are explained in more detail using schematic figures.

[0040] They show: Fig. 1 the basic structure of an RF circuit, Fig. 2 a configuration with several duplexers of the first frequency band, Fig. 3 an embodiment with several duplexers of the second frequency band, Fig. 4 a design with a tunable phase shifter, Fig. 5 an embodiment with several duplexers of the first frequency band and several duplexers of the second frequency band, Fig. 6 characteristic transmission curves of a typical diplexer, Fig. 7 characteristic transmission curves of a typical diplexer with slightly better isolation, Fig. 8 the effect of a phase shifter within an RF circuit using different curves, each representing a measure of an intermodulation product, at different values ​​of the phase shift, Fig. 9 the effect of a phase shifter within an RF circuit with an improved diplexer using different curves, each representing a measure of an intermodulation product, at different values ​​of the phase shift, Fig. 10 the dependence of the strength of intermodulation products on a phase shift by the phase shifter at the center frequency.

[0041] Fig. 1 shows a simple embodiment of an RF circuit HF-S with a first duplexer of a first frequency band DU-HB-1, a first duplexer of a second frequency band DU-LB-1, and a diplexer DI. A second signal path SP2 connects the first duplexer of the second frequency band DU-LB-1 to the second port P2 of the diplexer DI. A phase shifter PS is connected in the second signal path SP2. A first signal path SP1 connects the common port PG of the first duplexer of the first frequency band DU-HB-1 to the first port P1 of the diplexer DI. The common port PG of the diplexer DI can be connected to an antenna of a communications device. Each of the two duplexers has a transmit port TX and a receive port RX. The two duplexers can be connected to one or more transceiver circuits of a mobile radio device via the transmit and receive ports.

[0042] The following situation is critical when operating a conventional RF circuit: A transmit signal is coupled via both transmit ports TX of both duplexers, which travels to the diplexer DI via the signal paths SP1 and SP2. Due to the finite isolation of the diplexer DI, part of the transmit signal from the first frequency band is coupled into the second signal path SP2 in the direction of the duplexer of the second frequency band. Typically, the duplexers themselves are circuits with non-exclusively linear behavior, whereby in this case various TX signals converge at the TX filter of the duplexer of the second frequency band DU-LB-1. Due to non-linear effects of the duplexer of the second frequency band, an intermodulation product is created, which can potentially pass through the receive filter RX and interfere with or even prevent simultaneous reception by the communication device.For example, if the communication device is to transmit simultaneously in bands 3 and 5, an intermodulation product can arise at 1710 MHz - 824 MHz = 886 MHz. This lies within the band 5 receive frequency band (RX) and can therefore pass the receive filter virtually unattenuated.

[0043] In the present RF circuit HF-S, a signal leaking from the diplexer DI into the second signal path 2 is phase-shifted by the phase shifter so that mixing with the transmit signal for the second signal path SP2 at the duplexer is prevented. This prevents the intermodulation product from occurring at 886 MHz, or attenuates its intensity to such an extent that reception is possible without problems.

[0044] Fig. Figure 2 shows an embodiment in which three duplexers DU-HB-1, DU-HB-2, and DU-HB-3 are provided for the first frequency band. Using an individual switch SW, each of the duplexers can be coupled to the first signal path SP1.

[0045] Essentially analogous to this, Fig. 3 shows an embodiment of an RF circuit HF-S, in which three duplexers DU-LB-1, DU-LB-2, DU-LB-3 of the second frequency band are provided. Each of the three duplexers can be individually coupled to the second signal path SP2 using switches. Each of the three duplexers can have a dedicated phase shifter PS. The switches are preferably connected between the phase shifters and the diplexer.

[0046] Fig. Figure 4 shows how, instead of the three different phase shifters, a single phase shifter can be connected in the second signal path SP2. This phase shifter PS is designed and suitable for preventing or attenuating intermodulation products for all three duplexers of the second frequency band.

[0047] Fig. 5 shows an embodiment in which three duplexers are provided in both the first frequency band and the second frequency band.

[0048] Fig. Figure 6 shows characteristic curves of a typical diplexer with relatively low isolation.

[0049] Fig. Figure 7 shows characteristic curves of a typical diplexer with higher isolation.

[0050] Fig. Figure 8 shows the strength of the intermodulation interference in a carrier aggregation of the two Tx bands B5 and B7 when the diplexer of the Fig. 6 is used. The different curves each represent a different phase shift due to the phase shifter. The intermodulation product has frequency components around 880 MHz: B7-Tx (2540 MHz) - 2 x B5-Tx (2 x 830 MHz) = B5-Rx (880 MHz). The RF circuit includes a tunable phase shifter with an adjustable phase shift. Depending on the selected phase shift, intermodulation noise can be reduced by up to approximately 30 dB.

[0051] Accordingly, Fig. 9 different isolation values ​​of an RF circuit, which determine the “better” diplexer of the Fig. 7 with increased isolation - in addition to a tunable phase shifter as a phase shifter - contains. The different in Fig. The curves shown in Figure 8 represent the insulation values ​​with varied phase shift by the phase shifter. Analogous to Fig. 7, the reduction of intermodulation interference can be improved by up to 30 dB by selecting a suitable phase shift.

[0052] Overall, the Fig. 6 to 9 show that RF circuits with both poorer and better diplexers benefit significantly from the new circuit topology.

[0053] Fig. 10 shows the intensity of intermodulation products for RF circuits, each with one of the two Fig. 6 and a phase shifter designed as a phase shifter. It turns out that the improved isolation does indeed lead to a reduction in intermodulation products – but only if the phase shifter is optimally dimensioned and adjusted accordingly.

[0054] The RF circuit is not limited to the described or illustrated embodiments. An RF circuit may, in particular, contain additional circuit components, signal paths, filters, and switches. List of reference symbols DB-HP passband of the high-pass filter of the diplexer DB-LP passband of the low-pass filter of the diplexer DI Diplexer DU Duplexer DU-HB-1 first duplexer of the first frequency band DU-HB-2 second duplexer of the first frequency band DU-HB-3 third duplexer of the first frequency band DU-LB-1 first duplexer of the second frequency band DU-LB-2 second duplexer of the second frequency band DU-LB-3 third duplexer of the second frequency band HF-S RF circuit IS Isolation of the diplexer PG Shared Port RX receive port PS phase shifter SD switch SP1 first signal path SP2 second signal path TX send port

Claims

[1] RF circuit (RF-S) for Tx Carrier Aggregation, comprising - a diplexer (DI) with a first port (P1), a common port (PG) and a second port (P2), - a first duplexer (DU-HB-1) for a first frequency band with a transmit port (TX), a common port (PG) and a receive port (RX), - a first duplexer (DU-LB-1) for a second frequency band with a transmit port (TX), a common port (PG) and a receive port (RX), wherein the first frequency band is the 2 GHz band or the 2.5 GHz band and the second frequency band is the 1 GHz band, - a first signal path (SP1) between the common port (PG) of the first duplexer (DU-HB-1) of the first frequency band and the first port (P1) of the diplexer (DI), wherein the first signal path (SP1) connects the common port (PG) of the first duplexer (DU-HB-1) of the first frequency band to the first port (P1) of the diplexer (DI), - a second signal path (SP2) between the common port (PG) of the first duplexer (DU-LB-1) of the second frequency band and the second port (P2) of the diplexer (DI), - in the second signal path (SP2), a phase shifter (PS) which is provided to adapt the impedances of the first duplexer (DU-LB-1) of the second frequency band and of the diplexer (DI) for at least one harmonic of one of the frequency bands in such a way that at least one intermodulation product is reduced, wherein the phase shifter (PS) is tunable in its phase offset. [2] RF circuit according to the preceding claim, wherein the diplexer (DI) is a ceramic diplexer. [3] RF circuit according to one of the preceding claims, further comprising a second or more further duplexers (DU-HB-2, DU-HB-3) of the first frequency band, which can be connected in parallel to the first duplexer (DU-HB-1) of the first frequency band and to the first signal path (SP1). [4] RF circuit according to the preceding claim, further comprising a switch arrangement (SW) via which the first port (P1) of the diplexer (DI) can be connected to one or more of the duplexers (DU-HB-1, DU-HB-2, DU-HB-3) of the first frequency band. [5] RF circuit according to one of the preceding claims, further comprising a second or more further duplexers (DU-LB-2, DU-LB-3) of the second frequency band, which can be connected in parallel to the first duplexer (DU-LB-1) of the second frequency band and to the second signal path (SP2). [6] RF circuit according to the preceding claim, further comprising a switch arrangement (SW) via which the second port (P2) of the diplexer (DI) can be connected to one or more of the duplexers (DU-LB-1, DU-LB-2, DU-LB-3) of the second frequency band. [7] RF circuit according to one of the preceding claims, wherein a phase shifter (PS) is provided in the second signal path (SP2) for each duplexer (DU-LB-1, DU-LB-2, DU-LB-3) of the second frequency band. [8] Mobile radio device comprising an RF circuit (HF-S) according to one of the preceding claims. [9] Use of an RF circuit (HF-S) according to one of the preceding claims in a front-end circuit of a mobile radio device.

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