Tunable duplexer having a circulator

Abstract

A tunable duplexer is specified is disclosed. In an embodiment, the duplexer includes a transmission port, a reception port, a common port and a core having a first inductive element and a second inductive element. The duplexer further includes a first signal path electrically connecting the transmission port to the core, a second signal path electrically connecting the reception port to the core and a third signal path electrically connecting the common port to the core. A first tunable capacitive element electrically connects the first signal path to ground and a second tunable capacitive element electrically connects the second signal path to ground, wherein the first inductive element and the second inductive element are inductively and conductively coupled to one another.

Claims

1. A tunable duplexer comprising: a transmission port; a reception port; a common port; a core having a first inductive element and a second inductive element; a first signal path electrically connecting the transmission port to the core; a second signal path electrically connecting the reception port to the core; a third signal path electrically connecting the common port to the core; a first tunable capacitive element that electrically connects the first signal path to electric ground; a second tunable capacitive element that electrically connects the second signal path to the electric ground, wherein the first inductive element and the second inductive element are inductively and conductively coupled to one another; a first inductor-capacitor (LC) parallel circuit that electrically connects the first signal path to the electric ground; a second LC parallel circuit that electrically connects the second signal path to the electric ground; and a third LC parallel circuit that electrically connects the third signal path to the electric ground.

2. The tunable duplexer according to claim 1, wherein the core is a circulator.

3. The tunable duplexer according to claim 1, further comprising a third inductive element inductively and conductively connected to the first inductive element, wherein the third inductive element is inductively and conductively connected to the second inductive element, and wherein the second inductive element is electrically connected to the third signal path.

4. The tunable duplexer according to claim 1, further comprising a third capacitive element that electrically connects the third signal path to the electric ground.

5. The tunable duplexer according to claim 1, further comprising: a series capacitive element that is electrically connected in series in the first signal path; a series capacitive element that is electrically connected in series in the second signal path; and a series capacitive element that is electrically connected in series in the third signal path.

6. The tunable duplexer according to claim 1, further comprising: a series inductive element that is electrically connected in series in the first signal path; a series inductive element that is electrically connected in series in the second signal path; and a series inductive element that is electrically connected in series in the third signal path.

7. The tunable duplexer according to claim 1, the first and second inductive elements and the first and second tunable capacitive elements are formed as patterned metallizations in a multilayer substrate.

8. The tunable duplexer according to claim 1, further comprising a series capacitive element electrically connected in series in the third signal path.

9. The tunable duplexer according to claim 1, wherein the first inductive element is electrically connected to the first signal path and the second inductive element is electrically connected to the second signal path.

10. The tunable duplexer according to claim 9, wherein the first inductive element and the first tunable capacitive element form a resonant circuit connected to the electric ground that is suitable for producing a resonance at a center frequency in a selectable transmission frequency band, and wherein the second inductive element and the second tunable capacitive element form a resonant circuit electrically connected to the electric ground that is suitable for producing a resonance at a center frequency in a selectable reception frequency band.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Aspects of the duplexer and some embodiments are explained in more detail below with reference to schematic figures, in which:

(2) FIG. 1 shows an equivalent circuit diagram of a duplexer;

(3) FIG. 2 shows a further possible embodiment of the duplexer;

(4) FIG. 3 shows the operation of the circulator;

(5) FIG. 4 shows a further possible refinement of the duplexer;

(6) FIG. 5 shows a possible configuration of the duplexer with further circuit elements;

(7) FIG. 6 shows a possible implementation of circuit elements in a multilayer substrate;

(8) FIG. 7 shows electrical properties of a duplexer for a first set of selected operating frequencies; and

(9) FIG. 8 shows electrical properties of the duplexer from FIG. 7 with a second set of selected operating frequencies.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

(10) FIG. 1 essentially shows the equivalent circuit diagram of an embodiment of the duplexer DPX in which a central circuit core K essentially implements the interconnection of a transmission port TX, a reception port RX and a common port GP. In this case, the core K of the duplexer comprises the first inductive element IE1 and the second inductive element IE2. One side of each of the two inductive elements is electrically connected to one another at a central circuit node ZSK. The other ends of the inductive elements are electrically connected to the relevant sections of the signal paths to the relevant ports. As such, the first inductive element IE1 is electrically connected to the transmission port TX via the first signal path SP1. The second inductive element IE2 is electrically connected to the reception port RX via the second signal path SP2. The third signal path SP3 electrically connects the circuit core K to the common port GP. The third signal path SP3 is in this case likewise electrically connected to the central circuit node ZSK. The first signal path SP1 is electrically connected to ground via the first tunable capacitive element KE1. The second signal path is electrically connected to ground via the second tunable capacitive element KE2.

(11) The curved arrow with two arrow tips symbolizes the inductive coupling of the two inductive elements IE1, IE2 in the circuit core K. In one specific circuit element, the two inductive elements IE1, IE2 of the duplexer DPX are arranged relative to one another such that the desired inductive coupling that is needed for operation of the duplexer DPX is obtained.

(12) FIG. 2 illustrates how the connection of the tunable capacitive elements to the relevant inductive elements in the circuit core K forms a resonant circuit in order to produce the insertion loss of the duplexer in the relevant frequency band. As such, a first resonant circuit RK1 comprising the first tunable capacitive element KE1 and the first inductive element IE1 forms a resonant circuit to ground in order to produce the insertion loss in the transmission frequency band. The central circuit node ZSK is likewise electrically connected to ground for this purpose.

(13) Similarly, the second inductive element and the second tunable capacitive element form a resonant circuit in order to form the profile of the insertion loss in the reception frequency band.

(14) FIG. 3 illustrates the operation of the circuit core K, which in this case is in the form of a circulator. The three inductive elements in the circuit core K are electrically connected to one another centrally, and inductively coupled to one another. As such, particularly each of the inductive elements is inductively coupled to each of the other two inductive elements. Received signals that are received from the common port GP and are intended to be routed exclusively to the reception port RX can be split into a signal portion that propagates in a clockwise direction and a signal portion that propagates in a counterclockwise direction. Both signal portions preferably have a tiny phase offset at the location at which the circuit core K is electrically connected to the second signal path to the reception port, as a result of which said signal portions are constructively superimposed. The phase of the signal portions at the transmission port results in destructive superimposition, on the other hand, as a result of which the received signals cannot leave the duplexer at the transmission port TX.

(15) The same applies in a similar fashion to transmission signals that are coupled into the duplexer at the transmission port TX and interfere constructively at the common port GP, while the isolation is ensured by destructive interference at the reception port RX.

(16) Selection of the capacitance values of the two tunable capacitive elements allows the relative phase to be set on the frequency-dependent basis such that the duplexer can operate at different transmission frequencies and at different reception frequencies.

(17) FIG. 4 shows an embodiment of the duplexer DPX in which each of the three signal paths contains a series capacitive element SKE and a series inductive element SIE electrically connected in series with one another and in series with the signal path. The symmetrical arrangement of the series inductive and capacitive elements is not absolutely necessary in this case. The three signal paths can together also comprise just a single inductive or capacitive element that is electrically connected in one of the three signal paths in each case. The provision of two capacitive or two inductive elements in each case that are distributed over the three signal paths is also possible.

(18) Particularly the relevant series inductive element SIE may be embodied by conductor structures that serve to feed a signal to the duplexer.

(19) FIG. 5 shows an embodiment in which the signal paths additionally have their peripheral end electrically connected to ground via a parallel circuit comprising a capacitive element KE and an inductive element IE.

(20) This may allow better matching of the duplexer to external circuit environments, particularly impedance matching.

(21) The grounded inductive element at the common port GP also allows signals that have been caused by discharge of a static charge to be drained to ground such that the remainder of the circuit elements are not affected. In that case, the inductive element works an ESD protection element.

(22) FIG. 6 shows the possibility of integrating circuit elements as patterned metallizations SM in a multilayer substrate MLS. As such, capacitive elements KE may be formed by patterned metallization areas SMF. Inductive elements may be formed by plated-through holes DK made linearly or made in a manner looped through the substrate layers. In this case, the different substrate layers are formed by dielectric layers DL, between which metallization layers are arranged. The top of the multilayer substrate MLS may have further circuit elements, e.g. discrete circuit elements such as coils or capacitive elements having a high Q factor, arranged on it. A cover D may be provided in order to cover the circuit elements on the top of the multilayer substrate MLS. The underside of the multilayer substrate MLS may be provided with pads that are used to connect up the duplexer as part of a frontend circuit to an external circuit environment of a communication appliance.

(23) FIG. 7 shows computed absolute values of the matrix elements S.sub.2,1, S.sub.3,2, S.sub.3,1. As such, the curve marked by triangles shows the insertion loss for (S.sub.2,1) for transmission signals that propagate from the transmission port TX to the common port GP. The center frequency of the transmission band is set to 880.71 MHz in this case. The center frequency of the reception band is set to 930.59 MHz. The duplexer is thus set such that it operates at the frequencies of the FDD (FDD=Frequency Division Duplexing) band 8. The lowest insertion loss in the transmission band is 0.141 dB in this case. The lowest insertion loss in the reception band is 0.293 dB. The isolation between transmission signal path and received signal path is always better than 12 dB in this case.

(24) FIG. 8 shows the corresponding computed values for the frequencies of the FDD band 13. In this case, the transmission frequencies (center frequency 777.2 MHz) are above the reception frequency band (center frequency 751.27 MHz). The minimum insertion losses are 1.17 dB in the transmission frequency band and 0.65 dB in the reception frequency band.

(25) FIGS. 7 and 8 show instances of the same duplexer being matched to different frequency bands in this case, the orientations of transmission signal band and received signal band in relation to one another being reversed: when the transmission frequency band is below the reception frequency band in band 8, the transmission frequency band is above the reception frequency band in band 13.

(26) For conventional tunable duplexers, it is almost impossible in this case to deal with frequency bands having transposed transmission frequencies and reception frequencies and at the same time to have such low insertion losses.

(27) In this case, the tunable duplexers are not limited to the embodiments described or shown. Further embodiments with additional circuit elements in the circuit core or in the signal paths or duplexers whose signal ports have further filter circuits connected to them are likewise covered.