Abstract
A multiplexer circuit with good isolation characteristics and a compensated frequency characteristic at the transmission side is presented. The multiplexer circuit has a reception filter notch circuit (RFNC) active at a frequency within a passband of a reception filter (RXF) and coupled between an input port and a transmission filter (TXF).
Claims
1. A multiplexer circuit comprising an input port, a common port, an output port and a signal line between the input port and the common port, a transmission filter between the input port and the common port, a reception filter coupled to the output port, a reception filter notch circuit coupled between the input port and the transmission filter, wherein the reception filter has a passband and the reception filter notch circuit is active at a frequency within the passband of the reception filter.
2. The multiplexer of claim 1, wherein the reception filter comprises a capacitive element.
3. The multiplexer of claim 2, wherein the capacitive element of the reception filter notch circuit electrically connects the signal line to ground.
4. The multiplexer of claim 1, wherein the reception filter notch circuit is provided to create a notch in the transfer function S21.
5. The multiplexer of claim 1, wherein the multiplexer is a duplexer and the transmission filter and the reception filter are filters of the duplexer, or the multiplexer is a multiplexer of a degree higher than 2, and the multiplexer comprises an additional reception filter.
6. The multiplexer of claim 1, wherein the reception filter notch circuit improves reception cross isolation in a carrier aggregation system.
7. The multiplexer of claim 1, further comprising an impedance matching circuit between the input port and the transmission filter.
8. The multiplexer of claim 1, further comprising a power amplifier connected to the input port and the transmission filter and/or a low noise amplifier connected to the output port.
9. A frontend module, comprising the multiplexer of claim 1 and a power amplifier, wherein the circuit elements of the multiplexer and the circuit elements of the power amplifier are combined in a single component.
Description
[0048] Central aspects of the present multiplexer and details of preferred embodiments are presented and further explained by the accompanying schematic figures.
[0049] In the figures:
[0050] FIG. 1 illustrates the basic concept of the multiplexer.
[0051] FIG. 2 illustrates an example in the form of a duplexer.
[0052] FIG. 3 illustrates the use of a ladder-type-like configuration for transmission and reception filters.
[0053] FIGS. 4 to 6 illustrate the possibility of further matching elements at the common port.
[0054] FIG. 7 illustrates the use of a capacitance element in the reception filter notch circuit.
[0055] FIG. 8 illustrates a quadplexer.
[0056] FIG. 9 illustrates the use of an impedance matching circuit.
[0057] FIG. 10 illustrates the connection to power amplifier.
[0058] FIG. 11 illustrates the effects of a series element and a parallel element.
[0059] FIG. 12 illustrates the effect of an normal additional parallel element in enlarged view of the TX passband.
[0060] FIG. 13 illustrates an enlarged view of the passband frequencies with a normal additional parallel element.
[0061] FIG. 14 illustrates transmission characteristics of a multiplexer as described above.
[0062] FIG. 15 illustrates an enlarged view of the passband frequencies.
[0063] FIG. 1 shows a basic configuration of the multiplexer circuit MC. The multiplexer circuit MC has an input port IN, a common port CP and an output port OUT. The input port IN is provided to receive RF signals that should be transmitted and that should be received from an external circuit environment. The output port OUT is provided to submit received RF signals to an external circuit environment of the corresponding mobile communication device. The common port CP is the port via which transmission signals are transmitted and reception signals are received. To that end the common port CP can be connected to an antenna AN, e.g. via an antenna port (not shown). A signal path electrically connects the input port IN to the common port CP. In the signal path a transmission filter TXF is connected. Between the input port IN and the transmission filter TXF the reception filter notch circuit RFNC is arranged. It was recognized that taking a corresponding circuit from a reception filter RXF and placing it before the transmission filter TXF allows maintaining a good isolation level while making handling the frequency dependencies in the transmission signal path easier. The translation of the corresponding circuit elements from the reception filter RXF to the transmission signal side keeps the total number of circuit elements constant and thus maintains compatibility with the trend towards miniaturization.
[0064] It is to be noted that the reception filter RXF does not necessarily have to be the reception filter thatin combination with the transmission filter TXFestablishes a duplexer. The reception filter RXF can be another reception filter of a multiplexer of a higher degree. Then the reception filter has its own input port IN2 via which reception signals are received.
[0065] By removing the corresponding circuit component from its origin O in the reception filter RXF, designing the reception filter RXF is simplified.
[0066] FIG. 2 illustrates the possibility of establishing a duplexer: The transmission filter TXF and the reception filter RXF establish the two RF filters of the multiplexer circuit MC, which is realized as a duplexer.
[0067] Further, it is possible that the reception filter notch circuit RFNC is arranged before the transmission filter TXF and electrically connected in a shunt path between the signal path connected to the input port IN on the one side and to ground on the other side.
[0068] FIG. 3 illustrates the possibility of utilizing a ladder-type-like structure for the transmission filter TXF and for the reception filter RXF. A ladder-type-like filter comprises series elements such as series resonators SR electrically connected in series in the signal path SP. In shunt paths between the signal path and ground parallel resonators PR are arranged.
[0069] Such a ladder-type-like configuration can be used to establish bandpass filters or band rejection filters. In the case of a transmission filter and of a reception filter the use of a bandpass filter is preferred.
[0070] However, the reception filter notch circuit can be realized as a band rejection filter having its own ladder-type-like configuration between the signal path SP and ground.
[0071] Series resonators and parallel resonators can be electroacoustic resonators working with acoustic waves. Resonators can be SAW resonators (SAW=surface acoustic wave), BAW resonators (BAW=bulk acoustic wave), GBAW resonators (GBAW=guided bulk acoustic wave) and/or TFSAW resonators (TF=thin film).
[0072] In electroacoustic resonators electrode structures combined with a piezoelectric material convert between RF signals and acoustic waves. Acoustic energy is confined to a resonator area utilizing acoustic mirror structures.
[0073] FIG. 4 illustrates the use of matching elements ME arranged between an output port of the transmission filter TXF and the common port CP. As an alternative (compare FIG. 5) it is possible to arrange matching elements ME between the common port and the input port of the reception filter RXF.
[0074] FIG. 6 illustrates the possibility of providing matching elements ME between the output port of the transmission filter TXF and the common port CP and between the common port CP and the input port of the reception filter RXF.
[0075] The matching elements shown in FIGS. 4 to 6 can be used to match the output impedance of the transmission filter for the corresponding frequency ranges to the input impedance of the reception filter. In particular, a high input impedance at the input port of the reception filter is wanted for transmission frequencies, while a desired specific impedance, e.g. 25 ohms, 5 ohms, 100 ohms or 200 ohms, is wanted at the input port of the reception filter for reception frequencies. Correspondingly, the impedance at the output port of the transmission filter should be an open circuit impedance for reception frequencies and an impedance matched to 25 ohms, 50 ohms, 100 ohms or 200 ohms for transmission frequencies.
[0076] This is obtained by choosing capacitance and inductance values of capacitance and inductance elements of the matching elements ME that lead to the needed electric decoupling of the filters.
[0077] FIG. 7 shows the possibility of using a capacitance element as an essential element of the reception filter notch circuit RFNC. The capacity of the capacitance element can be chosen such that the wanted notch in the corresponding frequency range of the corresponding reception signal path is obtained.
[0078] FIG. 8 shows the possibility of realizing the multiplexer circuit as a quadplexer. In addition to the transmission filter TXF and the reception filter RXF an additional transmission filter TXF2 and an additional reception filter RXF2 are provided. It is not necessarily the case that the origin of the circuit elements of the reception filter notch circuit RFNC is in the reception filter directly associated with a transmission filter TXF. In the configuration shown in FIG. 8 the origin O of the circuit elements of the reception filter notch circuit RFNC is from a reception filter RXF associated to the second transmission filter TXF2. In this configuration the reception filter notch circuit can be used for RX cross isolation, e.g. in a carrier aggregation system.
[0079] FIG. 9 illustrates the possibility of having an impedance matching circuit IMC between the input port and the transmission filter TXF, in particular between the input port IN and the reception filter notch circuit RFNC.
[0080] FIG. 10 illustrates the additional possibility of having the impedance matching circuit and/or the transmission filter receive RF signals from the power amplifier PA.
[0081] Additionally or as an alternative it is possible to provide a low noise amplifier LNA in a reception signal path.
[0082] FIG. 11 illustrates the relevance of shunt elements and series elements to establish a bandpass filter, e.g. in a ladder-type-like configuration. It is possible that a shunt element, e.g. a shunt resonator electrically connecting a signal path to ground, causes a notch at a lower frequency. A series element, e.g. a series resonator in a ladder-type-like configuration, causes a notch at a higher frequency. If the shunt element is combined with the series element in the ladder-type configuration, the combined effects of shunt and series elements create the shown transmission characteristic in the form of a passband.
[0083] When further frequency requirements are necessary, e.g. with the presence of a reception frequency band RX near a transmission frequency band, then additional measures are needed. In this case, an additional shunt element can be used to create an additional notch. In FIG. 12 (and in an enlarged view in FIG. 13) it is shown that isolation is improved. However, in the transmission frequency band an unwanted additional attenuation is obtained together with a passband ripple (the dashed line shows the effect of the additional notch element arranged at the reception side of a duplexer).
[0084] In contrast, FIGS. 14 and 15 (in an enlarged view) show transfer characteristics for the presented multiplexer circuit topology. It can be seen that in FIG. 14 the isolation is improved in the frequency range above the transmission frequency band while (compare FIG. 15) the shape of the transmission frequency band remains undisturbed.
[0085] The multiplexer circuit and the frontend module are not limited to the shown embodiments. Multiplexer circuits can comprise further circuit elements and/or further signal paths. Frontend modules can comprise further circuit components integrated therein.
LIST OF REFERENCE SIGNS
[0086] AN: antenna [0087] CE: capacitance element [0088] CP: common port [0089] IN: input port [0090] IN2: input port of the reception filter RXF [0091] IN3: third input port [0092] LNA: low noise amplifier [0093] MC: multiplexer circuit [0094] ME: matching elements [0095] O: origin of the circuit elements of the reception filter notch circuit [0096] OUT: output port [0097] OUT2: second output port [0098] PA: power amplifier [0099] PR: parallel resonator [0100] RFNC: reception filter notch circuit [0101] SR: series resonator [0102] TXF: transmission filter
