RF FILTER WITH INCREASED BANDWIDTH AND FILTER COMPONENT

Abstract

An RF filter (BPF) with an increased bandwidth is provided. The filter comprises a half-lattice topology and a phase shifter (PS) comprising inductively coupled inductance elements in a parallel branch parallel to a first segment (S1) of a signal path (SP) between a first port (P1) and a second port (P2) of the filter.

Claims

1. A half lattice filter, comprising: an input port, an output port and a signal path between the input port and the output port, a first segment in the signal path, a parallel branch that is electrically connected in parallel to the first segment of the signal path, a first electro acoustic resonator in the first segment, an impedance element in the parallel branch, and a phase shifter electrically connected in the parallel branch in series to the impedance element, wherein the phase shifter comprises two inductively coupled inductance elements.

2. The half lattic filter of claim 1, wherein the impedance element is selected from a capacitance element and an electro acoustic resonator.

3. The half lattic filter of claim 1, where each of the two inductively coupled inductance elements has one connection coupled to ground.

4. The half lattic filter of claim 1, wherein the phase shifter comprises a first capacitance element electrically connected to a first terminal and/or to a second terminal of the phase shifter.

5. The half lattic filter of claim 4, wherein the phase shifter comprises a second capacitance element electrically connected to a second terminal of the phase shifter.

6. The half lattic filter of claim 5, wherein the phase shifter comprises a third capacitance element electrically connecting the two inductively coupled inductance elements to ground.

7. The half lattic filter of claim 1, further comprising a second electro acoustic resonator electrically connected in a signal path between the first electro acoustic resonator and a second port.

8. The half lattic filter of claim 4, further comprising a second capacitance element electrically connected in the parallel branch between the first capacitance element and a second port and a third capacitance element electrically connected in the parallel branch between the second capacitance element and the second port.

9. The half lattic filter of claim 6, further comprising a fourth capacitance element electrically connected between the parallel branch and ground.

10. The half lattic filter of claim 1, further comprising a first impedance matching circuit electrically connected in the a signal path between a first port and the first electroacoustic resonator and/or a second impedance matching circuit electrically connected in a signal path between the first electroacoustic resonator and a second port.

11. The half lattic filter of claim 1, further comprising a plurality of capacitance elements, wherein the plurality of capacitance elements are combined with the electro acoustic resonator in an acoustic package.

12. The half lattic filter of claim 1, being a band pass filter with a relative bandwidth Δf with 13%<=Δf<=24%.

13. The half lattic filter of claim 1, wherein the two inductively coupled inductance elements are established in a multilayer carrier substrate.

14. The half lattic filter of claim 13, wherein the multilayer carrier substrate is selected from a LTCC substrate, a HTCC substrate, a laminate, a substrate for integrated passive devices.

15. The half lattic filter of claim 1, wherein the electro acoustic resonator is selected from a BAW resonator, a SAW resonator, a GBAW resonator, a TF-SAW resonator, or a TC-SAW resonator.

Description

[0048] In the figures:

[0049] FIG. 1 shows a basic construction of a bandpass filter;

[0050] FIG. 2 shows a basic construction of a phase shifter;

[0051] FIG. 3 shows the possibility of having a second electro acoustic resonator;

[0052] FIG. 4 shows the possibility of establishing the impedance element as a capacitance element;

[0053] FIG. 5 shows one parallel capacitance element per inductance element in the phase shifter;

[0054] FIG. 6 shows the use of a single capacitance element between the first terminal and the second terminal of the phase shifter;

[0055] FIG. 7 illustrates the possibility of using a single capacitance element for shunting both inductance elements;

[0056] FIG. 8 illustrates a possible combination of the phase shifter and the other circuit elements of the bandpass filter;

[0057] FIG. 9 illustrates another approach to electrically combine the circuit elements of the phase shifter with the other circuit elements of the bandpass filter;

[0058] FIG. 10 shows a cross-section through a multilayer filter component;

[0059] FIG. 11 shows phase delays of different phase shifter topologies;

[0060] FIG. 12 shows the insertion loss of different phase shifter topologies;

[0061] FIG. 13 shows a comparison between a proposed filter (curve 1) and a conventional filter (curve 3);

[0062] FIG. 14 shows a wideband view of the parameters shown in FIG. 13; and

[0063] FIG. 15 shows the right skirt performances of the proposed and of a conventional filter.

[0064] FIG. 1 shows basic circuit elements of a bandpass filter BPF. The bandpass filter BPF comprises a first port P1 and a second port P2. It is possible but not necessary that the first port P1 is an input port while the second port P2 is an output port o the bandpass filter BPF. The direction of propagation of RF signals can go from the first port P1 to the second port P2 or from the second port P2 to the first port P1.

[0065] The signal path SP is arranged between the first port P1 and the second port P2. The signal path comprises a first segment S1. The first segment S1 is arranged between a first node N1 and a second node N2. Further, a parallel branch PB is electrically connected in parallel to the first segment S1 between the first node N1 and the second node N2. In the first segment S1 a first electro acoustic resonator EAR1 is electrically connected between the first port P1 and the second port P2. In the parallel branch PB a series connection of an impedance element IE and a phase shifter PS is electrically connected. It is possible that the impedance element IE is electrically connected between the first node Ni and the phase shifter PS while the phase shifter PS is electrically connected between the impedance element IE and the second port P2 or the second node N2.

[0066] FIG. 2 illustrates a basic embodiment of the phase shifter PS. The phase shifter PS has a first terminal T1 and a second terminal T2 and a connection to ground. The first terminal T1 can be an input terminal and the second terminal T2 can be an output terminal or vice versa. The phase shifter PS comprises a first inductance element INE1 and a second inductance element INE2. The first and the inductance elements establish inductively coupled inductance elements as indicated by the arrow. The first inductance element INE1 electrically connects the first terminal T1 to ground. The second inductance element INE2 electrically connects the second terminal T2 to ground.

[0067] The coupling between the inductance elements can be a direct coupling (k=1) or an opposite coupling (k)−1).

[0068] With the first terminal T1 the phase shifter PS can be electrically connected to or coupled to the impedance element shown in FIG. 1. With the second terminal T2 the phase shifter PS shown in FIG. 2 can be electrically connected to the second node N2 shown in FIG. 1.

[0069] The configuration comprising the topology shown in FIG. 1 with the embodiment of the phase shifter PS shown in FIG. 2 provides a substantially increased bandwidth while maintaining excellent other filter properties.

[0070] FIG. 3 illustrates the possibility of using a second electro acoustic resonator EAR2 in the bandpass filter BPF as the impedance element IE.

[0071] FIG. 4 illustrates an alternative approach where the impedance element IE is realized by a capacitance element CE.

[0072] The difference between the topologies shown in FIGS. 3 and 4 is that the impedance element IE shown in FIG. 3 is acoustically active while the impedance element IE shown in FIG. 4 is acoustically inactive.

[0073] However, the basic construction of the two impedance elements can be essentially similar except for the acoustic activity.

[0074] FIG. 5 shows a further possibility of providing the phase shifter PS. In addition to the inductively coupled inductance elements INE1, INE2 a first capacitance element CE1 is electrically connected between the first terminal and ground. A second capacitance element CE2 is electrically connected between the second terminal T2 and ground.

[0075] FIG. 6 shows a possibility of a phase shifter PS where in addition to the first and second coupled inductance elements INE1, INE2 a first capacitance element CE1 is connected between the first terminal T1 and the second terminal T2.

[0076] The two capacitance elements electrically connected in parallel to the inductance elements can be optionally present in the phase shifter shown in FIG. 6.

[0077] FIG. 7 shows the possibility of shunting the corresponding terminals of the coupled inductance elements INE1, INE2 via a specifically dedicated node N and via a third capacitance element CE3 to ground.

[0078] The capacitance element shown in FIG. 6 and the two capacitance elements shown in FIG. 5 can be optionally present in the phase shifter PS of FIG. 7.

[0079] FIG. 8 shows a possible combination of the circuit elements of the phase shifter in combination with the other circuit elements of the bandpass filter BPF.

[0080] In addition, impedance matching circuits can also be present.

[0081] The topology of the bandpass filter BPF shown in FIG. 8 comprises an additional, second electro acoustic resonator EAR2 between the second node and the second port P2. A first impedance matching circuit IMC1 is electrically arranged between the first port P1 and the first node. A second impedance matching circuit IMC2 is electrically configured between the second electro acoustic resonator EAR2 and the second port P2. In the parallel branch the impedance element IE is realized as a first capacitance element CE1. An additional, second capacitance element CE2 is arranged between the first capacitance element CE1 and the second node. A further, third capacitance element CE3 is electrically connected between the second capacitance element CE2 and the second node. Thus, the three capacitance elements CE1, CE2 and CE3 establish a series connection in the parallel branch PB.

[0082] One terminal of the first coupled inductance elements INE1 is connected to a node between the first capacitance element CE1 and the second capacitance element CE2. The respective other terminal of the inductance element INE1 is connected to ground. Correspondingly, a first terminal of the second coupled inductance element INE2 is electrically connected to a node between the second capacitance element CE2 and the third capacitance element CE3. The respective other terminal of the inductance element is connected to ground.

[0083] The two electro acoustic resonators EAR1, EAR2 together with the three capacitance elements CE1, CE2, CE3 are realized in the acoustic package AP. The respective other circuit elements, e.g. of the first and of the second impedance matching circuit IMC1, IMC2 and the inductance elements are established outside the acoustic package, e.g. within a multilayer construction of the carrier substrate.

[0084] The first and the second impedance matching circuits IMC1, IMC2 can comprise LC elements electrically configured in Pi and Tee configurations to match an external circuit environment of the bandpass filter BPF at the corresponding ports P1, P2. The matching impedance can be 50 ohm, 100 ohm or 200 ohm.

[0085] FIG. 9 illustrates a configuration where the parallel branch PB is electrically connected to ground at the place of the second node via a fourth capacitance element CE4. A second electro acoustic resonator EAR2 is electrically connected between the second node N2 and the second port P2. Further, a first impedance matching circuit IMC1 and a second impedance matching circuit IMC2 are electrically connected between the first port P1 and the first node and between the second electro acoustic resonator EAR2 and the second port P2, respectively.

[0086] While the inductively coupled inductance elements electrically shunt the parallel branch PB to ground in the topology shown in FIG. 8, the inductance elements INE1, INE2 are electrically connected in series in the parallel branch PB and the node between the two inductance elements INE1, INE2 is electrically connected to ground.

[0087] The two electro acoustic resonators EAR1, EAR2 and the impedance element IE are realized as a first capacitance element CE1 and the fourth capacitance element CE4 are realized in the acoustic package AP while the respective other circuit elements are realized outside the acoustic package AP, e.g. in a multilayer construction of the carrier substrate.

[0088] FIG. 10 illustrates a cross-section through a possible multilayer filter component MLFC. The multilayer filter component comprises a multilayer carrier substrate with a plurality of layers L. The layers L comprise or consist of a dielectric material. Conductive structures realized as metallized patterns between the layers L realize passive circuit elements such as impedance elements like inductance elements IN and capacitance elements CE. The acoustic package AP is arranged at the top side of the multilayer carrier substrate and electrically connected to the impedance elements in the substrate. A connection can take place via a bump connection or via wire bonding connections. The sensitive MEMS structures (MEMS=micro electro mechanical system) are protected in a hermetically sealed environment HS.

[0089] FIG. 11 shows a comparison of three different phase shifter topologies. Curve 1 shows a three-stages high pass phase shifter. Curve 3 shows a three-stages low pass phase shifter. In contrast, curve 2 shows a phase shifter comprising two coupled parallel coils as suggested above. The phase error (slope of the phase curve) for frequencies around 4.2 GHz is much smaller in curve 2, i.e., a phase shift around 180° degrees is achieved for a much wider frequency range. In this context it is to be noted that a phase difference of 180° is equal to a phase difference of −180°. The vertical boundaries of −180° and 180° are choosen arbitrarily. Thus, a relatively stable phase in a wide frequency range, e.g. from 3 GHz to 6 GHz is obtained.

[0090] FIG. 12 shows the corresponding insertion loss of the phase shifters described in the context of FIG. 11. Curve 2 denotes the insertion loss of the phase shifter with the two coupled inductance elements. A wide frequency range with a low insertion loss and a phase shift around 180° are simultaneously obtained.

[0091] FIG. 13 shows the passband performance of the bandpass filter shown in FIG. 8 without a coupling of the inductance elements (curve 1) and the corresponding passband performance of the bandpass filter according to FIG. 9 with coupled inductance elements (curve 3). The bandwidth specification is fulfilled in both filters, the important point as mentioned in the following paragraph, is that both passband bandwidth specification and isolation level above the passband can be simultaneously achieved.

[0092] FIG. 14 illustrates the corresponding performances shown in FIG. 13 in a wider frequency range

[0093] FIG. 15 shows the right skirt performance of a topology indicated by FIG. 8 without the coupling of the inductance coils (curve 1) and the right skirt performance of the filter shown in FIG. 9 including the coupling between the inductance elements (curve 3) showing that the isolation levels above the passband are significantly improved fulfilling now the specified parameters.

[0094] The above-described bandpass filters provide a substantially better close-in suppression above the passband while other important filter parameters are essentially maintained.

[0095] The filter or the filter component are not limited to the specific details shown in the figures or described above. Filters or filter components can comprise further circuit elements, e.g. for impedance matching, and further structural elements, e.g. for embedding impedance elements in a multilayer substrate or protecting sensitive MEMS structures like resonators from detrimental influences.

LIST OF REFERENCE SIGNS

[0096] AP: acoustic package [0097] BPF: bandpass filter [0098] CE: capacitance element [0099] CE1, CE2, CE3 CE4: capacitance element [0100] EAR1, EAR2: first, second electro acoustic resonator [0101] HS: hermetical seal [0102] IE: impedance element [0103] IMC1, IMC2: first, second impedance matching circuit [0104] IN: inductance element [0105] INE1, INE2: first, second inductively coupled inductance element [0106] L: layer [0107] MLFC: multilayer filter component [0108] N: node [0109] N1, N2: first, second node in the signal path [0110] P1, P2: first, second port of the filter [0111] PB: parallel branch [0112] PS: phase shifter [0113] S1: first segment of signal path [0114] SP: signal path [0115] T1, T2: first, second terminal of the phase shifter [0116] W: wire connection through one or more layers