COMBINED IMPEDANCE MATCHING AND RF FILTER CIRCUIT

Abstract

What is specified is a combined impedance matching and RF filter circuit having improved impedance matching in conjunction with good frequency-tunability of the filter circuit. The circuit comprises a reactance elimination circuit for reducing the reactance and a tunable RF filter circuit, which is frequency-tunable and can carry out a resistance matching.

Claims

1. A combined impedance matching and RF filter circuit, comprising a signal input, a signal output, a reactance elimination circuit between the signal input and the signal output, a frequency-tunable RF filter circuit interconnected in series with the reactance elimination circuit between the signal input and the signal output, wherein the signal input and the signal output are provided for being interconnected with circuit components having different connection impedances, the reactance elimination circuit makes available an output impedance without reactance, the tunable RF filter circuit is suitable for carrying out a matching of the resistance with unchanged reactance.

2. The circuit according to claim 1, wherein the tunable RF filter circuit comprises a resistance matching circuit on the input or output side or the input and output side.

3. The circuit according to claim 1, wherein the tunable RF filter circuit comprises at least one of tunable capacitive or inductive elements for the frequency tuning.

4. The circuit according to claim 1, wherein the tunable RF filter circuit is constructed from passive circuit elements.

5. The circuit according to claim 1, wherein the reactance elimination circuit comprises at least one of capacitive or inductive elements.

6. The circuit according to claim 5, wherein the reactance elimination circuit comprises at least one of tunable capacitive or inductive elements for reducing the absolute value of the reactance.

7. The circuit according to claim 1, wherein the tunable RF filter circuit comprises a filter core having a first impedance element in a first signal route and having electromagnetically coupled impedance elements interconnected in series in a second signal route interconnected in parallel with the first signal route.

8. The circuit according to claim 1, which is interconnected in a receiving or transmitting path of a mobile communication device.

9. The circuit according to claim 1, which is interconnected together with a further circuit according to claim 1 in a mobile communication device, wherein the two tunable RF filter circuits together form a duplexer.

10. The circuit according to claim 1, comprising two reactance elimination circuits and a tunable RF filter circuit interconnected between the two reactance elimination circuits.

11. An amplifier circuit, comprising a combined impedance matching and RF filter circuit according to claim 1, an antenna connection, and either a power amplifier interconnected with the signal input of the combined impedance matching and filter circuit, or a low noise amplifier interconnected with the signal output of the combined impedance matching and filter circuit, wherein the combined impedance matching and RF filter circuit are interconnected between the amplifier and the antenna connection.

12. A combined impedance matching and RF filter circuit, comprising a signal input, a signal output, a reactance elimination circuit between the signal input and the signal output, a frequency-tunable RF filter circuit interconnected in series with the reactance elimination circuit between the signal input and the signal output, wherein the signal input and the signal output are provided for being interconnected with circuit components having different connection impedances, the reactance elimination circuit makes available an output impedance without reactance, the tunable RF filter circuit is suitable for carrying out a matching of the resistance with unchanged reactance the tunable RF filter circuit comprises a filter core having a first impedance element in a first signal route and having electromagnetically coupled impedance elements interconnected in series in a second signal route, which is interconnected in parallel with the first signal route.

13. The circuit according to claim 2, wherein the tunable RF filter circuit comprises at least one of tunable capacitive or inductive elements for the frequency tuning or the reactance elimination circuit comprises at least one capacitive or inductive elements.

14. The circuit according to claim 2, wherein the tunable RF filter circuit comprises a filter core having a first impedance element in a first signal route and having electromagnetically coupled impedance elements interconnected in series in a second signal route interconnected in parallel with the first signal route.

15. The circuit according to claim 3, wherein the tunable RF filter circuit comprises a filter core having a first impedance element in a first signal route and having electromagnetically coupled impedance elements interconnected in series in a second signal route interconnected in parallel with the first signal route.

16. The circuit according to claim 2, comprising two reactance elimination circuits and a tunable RF filter circuit interconnected between the two reactance elimination circuits.

17. The circuit according to claim 3, comprising two reactance elimination circuits and a tunable RF filter circuit interconnected between the two reactance elimination circuits.

18. The circuit according to claim 3, wherein the tunable RF filter circuit comprises a resistance matching circuit on the input or output side or the input and output side, the circuit further comprising two reactance elimination circuits and a tunable RF filter circuit interconnected between the two reactance elimination circuits.

Description

[0079] In the figures:

[0080] FIG. 1: shows the reactance elimination circuit XES and the tunable RF filter circuit AHF, which together form the essential components of the combined impedance matching and RF filter circuits KIAF,

[0081] FIG. 2: shows one possible arrangement of two reactance elimination circuits in the tunable RF filter circuit,

[0082] FIG. 3: shows one possible circuit topology of the tunable RF filter circuit,

[0083] FIG. 4: shows more extensive details of one possible configuration of the tunable RF filter circuit,

[0084] FIG. 5: shows details of an alternative configuration of the tunable RF filter circuit,

[0085] FIG. 6: shows details of a tunable RF filter circuit comprising acoustic, ceramic or MEMS-based resonators,

[0086] FIG. 7a: shows one possible use of the circuit in a mobile communication device,

[0087] FIG. 7b: shows one possible use of the circuit in a receiving branch of a mobile communication device,

[0088] FIG. 7c: shows one possible use of the circuit comprising two reactance elimination circuits,

[0089] FIG. 8: shows one possible use of the circuit in a communication device comprising further circuit components,

[0090] FIG. 9: shows a mobile communication device comprising at least two of the circuits described.

[0091] FIG. 1 shows the two important circuit components of the combined impedance matching and RF filter circuit KIAF. A reactance elimination circuit XES and a frequency-tunable RF filter circuit AHF are interconnected between the signal input IN of the circuit and the signal output OUT of the circuit. A port of an external circuit environment, e.g. of an amplifier, which has a connection impedance Z=R+jX, can be connected to the signal input IN. In this case, R is the resistance, while X is the reactance. The reactance elimination circuit makes available at its output facing the signal output OUT an output impedance whose reactance X is substantially 0. The impedance Z is thus substantially reduced to a real value having an absolute value around the value R.

[0092] The tunable RF filter circuit AHF is configured such that it can carry out a matching of the resistance R, without changing the value of the reactance X. The tunable RF filter circuit AHF thus comprises the functionality of a resistance matching circuit RAS.

[0093] At its signal output OUT the circuit KIAF thus makes available an RF signal corrected with regard to undesired signals by the filter effect of the tunable RF filter circuit. The signal is made available at a port with a connection impedance adjusted with regard to its reactance and its resistance such that signals can be forwarded without reflection to a circuit environment connected to the signal output OUT.

[0094] Since the matching of the reactance and of the resistance is carried out in different assemblies of the circuit, in particular the reactance elimination circuit XES can be simplified and optimized with regard to a low insertion loss such that the entire circuit operates with improved energy efficiency.

[0095] In a transmitting branch, the connection IN can be connected to a power amplifier and, in a receiving branch, the connection IN can be connected to a low noise amplifier. In this case, the designations IN and OUT are interchangeable insofar as they denote the signal input and signal output, respectively.

[0096] FIG. 2 shows one possible form of the tunable RF filter circuit AHF, in which a respective resistance matching circuit RAS is arranged both on the input side and on the output side. In this regard, the input-side resistance matching circuit RAS is arranged between the input E of the tunable RF filter circuit AHF and a filter core FK substantially responsible for the filter effect of the tunable RF filter circuit. The output-side resistance matching circuit RAS is arranged between the filter core FK and the output A of the tunable RF filter circuit AHF.

[0097] If two resistance matching circuits RAS exist in the tunable RF filter circuit AHF, then the matching of the resistance can be carried out in two stages. A single-stage matching is likewise possible; the input-side or the output-side resistance matching circuit can then be omitted.

[0098] However, it is also possible for the filter core FK itself to realize not only the filter effect but also additionally a resistance matching.

[0099] Via the input E of the tunable RF filter circuit, the latter can be interconnected with the reactance elimination circuit XES. The output A of the tunable RF filter circuit can correspond to the signal output OUT of the circuit. It is also possible for another resistance matching circuit RAS to be arranged between the output A of the tunable RF filter circuit in FIG. 3 and the signal output OUT in FIG. 1.

[0100] FIG. 3 shows an equivalent circuit diagram of one possible tunable RF filter circuit AHF, in which a signal path SP is arranged between an input E and an output A. In this case, the signal path SP comprises two parallel-connected partial sections, namely the first signal route SW1 and the second signal route SW2. An impedance element IMP is interconnected in the first signal route SW1. The impedance element IMP can be realized as a capacitive element or as an inductive element. The three resonant circuits RK1, RK2, RK3 are arranged one after another in the second signal route SW2. The resonant circuits are electrically or magnetically coupled and each comprise at least one tunable impedance element. Each of the three resonant circuits interconnects the second signal route with ground.

[0101] In this case, the first resonant circuit RK1 is coupled to the input E. In this case, the third resonant circuit RK3 is coupled to the output A. Those resonant circuits which are coupled to the input E or to the output A directly rather than via another resonant circuit constitute the so-called outer resonant circuits. These two outer resonant circuits thus enclose the other resonant circuit(s), which thus constitute inner resonant circuits.

[0102] In the equivalent circuit diagram in FIG. 3, therefore, the first resonant circuit RK1 and the third resonant circuit RK3 constitute the outer resonant circuits, while the second resonant circuit RK2 constitutes the (sole) inner resonant circuit.

[0103] The electrical and/or magnetic coupling of the resonant circuits is symbolized by the coupling designated by K. In this case, the first resonant circuit RK1 is electrically and/or magnetically coupled to the second resonant circuit RK2. The second resonant circuit RK2 is also coupled to the third resonant circuit RK3 besides the first resonant circuit RK1.

[0104] Via the coupling of the resonant circuits, an electrical signal can be forwarded from resonant circuit to resonant circuit, such that an RF signal can propagate in the second signal route SW2 as well.

[0105] FIG. 4 shows one possible equivalent circuit diagram of the tunable RF filter circuit in which the resonant circuits are realized as LC circuits. Each resonant circuit, shown here on the basis of the example of the first resonant circuit RK1comprises a parallel connection of an inductive element IE and a tunable capacitive element AKE. The tunable capacitive element AKE in this case constitutes the tunable impedance element of the corresponding resonant circuit. Conversely, each resonant circuit could also comprise a tunable inductive element. The corresponding parallel-connected impedance element of the resonant circuit would then be a capacitive element.

[0106] The tunable capacitive element AKE is interconnected with a control logic STL. The control logic STL comprises circuit elements that can be used to receive a control signal of an external circuit environment. The control signal of the external circuit environment is interpreted and control signals are output to the individual tunable capacitive elements AKE via corresponding signal lines SL.

[0107] The electromagnetic coupling between the resonant circuits is realized by a capacitive coupling of capacitive elements KE as coupling elements. For this purpose, each resonant circuit essentially comprises an electrode of a capacitive element KE via which it is coupled to the adjacent resonant circuit or the adjacent resonant circuits. In this case, a coupling via capacitive elements KE essentially constitutes a capacitive electrical coupling. In this case, the quality factor Q of said capacitive elements is permitted to be lower than the quality factor Q of the elements used in the resonant circuits.

[0108] The input-side resonant circuit can comprise a tunable capacitive element whose capacitance is adjustable in a range around 34.34 pF. At the input of the tunable RF filter circuit, there may be present in the signal path in series a further tunable capacitive element (not shown), the capacitance of which is adjustable at least in a range of between 1 and 5 pF. In this regard, a good matching to impedances of between 5 and 50 ohms is possible. The range of the capacitance can also be chosen such that good matchings to customary impedances with a magnitude of 5, 10, 25, 50, 100, 200 and 500 ohms are possible. A 5 ohm matching is achieved in the case of 5 pF in the signal path and 34.34 pF relative to ground. A 50 ohm matching is achieved in the case of pF in the signal path and 38.81 pF relative to ground.

[0109] FIG. 5 shows the equivalent circuit diagram of the tunable RF filter circuit in which the coupling between the resonant circuits RK is effected inductively. In this case, each resonant circuit has at least one inductive element IE via which a coupling to another inductive element of the corresponding resonant circuit is effected. Since the first resonant circuit RK1 is only inductively coupled to the second resonant circuit RK2, the first resonant circuit RK1 needs only one inductive element IE1 for coupling. The second resonant circuit RK2 is inductively coupled both to the first resonant circuit RK1 and to the third resonant circuit and therefore requires two inductive elements.

[0110] Whether the resonant circuits are coupled inductively or capacitively is unimportant for the fact that RF signals can be transmitted, such that the series arrangement of resonant circuits constitutes the second signal route SW2.

[0111] The capacitive elements for coupling between the resonant circuits in FIG. 5 and the inductive elements for coupling the resonant circuits in FIG. 6 are in this case arranged and configured such that the correct degree of coupling is obtained. In this case, the degree of coupling can be set by the distance between the electrodes or the electrode area or the coil shape, coil size and coil distance.

[0112] In each case two inductively coupled inductive elements of adjacent resonant circuits here essentially form a transformer circuit.

[0113] FIG. 6 shows an equivalent circuit diagram of the tunable RF filter circuit in which the resonant circuits comprise an acoustic resonator AR besides a tunable capacitive element AKE. Acoustic resonators are distinguished by high quality factors and at the same time by small dimensions. However, since they cause comparatively high production costs and require measures for decoupling and for protection against interfering ambient conditions on account of their mechanical mode of operation, the use of LC components may be preferred. Other types of resonators such as ceramic resonators, disk resonators, cavity resonators, MEMS-based resonators and the like are likewise possible.

[0114] FIG. 7a shows one possible application of the circuit between an amplifier, e.g. a power amplifier, and an antenna connection of a mobile communication device, which is interconnected with an antenna ANT. The sudden change in impedance from the amplifier to the antenna is generally particularly large, but the splitting of the matching into a matching of the reactance and a matching of the resistance brings about a particularly good matching in conjunction with a relatively simple construction even with the use of a tunable filter.

[0115] FIG. 7b shows one possible application of the circuit between an amplifier, e.g. a low noise amplifier, and an antenna connection of a mobile communication device, which is interconnected with an antenna ANT.

[0116] FIG. 7c shows one possible application of the circuit between an amplifier and an antenna connection of a mobile communication device. The amplifier may be depending on the direction of the RF signala power amplifier in a transmitting path or a low noise amplifier in a receiving path or both in a duplexed signal path. The task of eliminating the reactance is divided between two separate circuit segments. A first section of the reactance elimination circuit XES is interconnected between the antenna ANT and the tunable RF filter AHF and a second section of the reactance elimination circuit XES is interconnected between the tunable RF filter AHF and the antenna ANT. In this regard, the variability in the reduction of the reactance is increased.

[0117] FIG. 8 shows one possible application in which the tunable RF filter AHF is part of a duplexer DU. The tunable RF filter in this case constitutes a bandpass filter which, together with a further, if appropriate tunable, bandpass filter of a parallel signal path, ensures the filter effect in conjunction with good isolation of the duplexer.

[0118] FIG. 9 shows a double application of the circuit KIAF, which is used both in a transmitting path between a power amplifier PA and an antenna connection and in a reception signal between a low noise amplifier LNA and the antenna connection.

[0119] The circuit in this case is not restricted exclusively to the exemplary embodiments shown; circuits comprising further filters, resonant circuits or impedance matching sections are likewise encompassed. Uses other than the uses shown above in transmitting or receiving paths or in a duplexer are also possible.

LIST OF REFERENCE SIGNS

[0120] A: Output of the tunable RF filter circuit [0121] AHF: Tunable RF filter circuit [0122] ANT: Antenna [0123] DU: Duplexer [0124] E: Signal input of the tunable RF filter circuit [0125] FK: Filter core [0126] IMP: Impedance element [0127] IN: Signal input of the circuit [0128] KIAF: Combined impedance matching and RF filter circuit, also referred to just as circuit for the sake of simplicity [0129] LNA: Low noise amplifier [0130] OUT: Signal output of the circuit [0131] PA: Power amplifier [0132] RAS: Resistance matching circuit [0133] SP: Signal path [0134] SW1, SW2: First, second signal route [0135] XES: Reactance elimination circuit