These and other aspects of the invention are apparent from and will be elucidated, by way of non-limitative example, with reference to the embodiment(s) described hereinafter.
In the drawings:
FIG. 1 shows a first embodiment of a resonant conducting track arrangement, which is similar to a short-circuited capacitor;
FIG. 2 shows a further embodiment of a resonant conducting track arrangement which has similarities to an open coil;
FIGS. 3
a and 3b show examples of multilayered arrangements of the first and second embodiment;
FIG. 4 shows an example of a bandpass filter with two resonators according to the embodiment in FIG. 1 together with an example of a layered structure in a multilayered substrate;
FIG. 5 shows the calculated frequency response of the filter in FIG. 4;
FIG. 6 shows a balancing transformer or balun with a resonator according to FIG. 1;
FIG. 7 shows an embodiment of a combined filter, balancing and adaptor network with two resonators according to FIG. 1;
FIG. 8 shows the calculated frequency response of the network according to FIG. 7;
FIGS. 9
a and 9b show schematically the layer offset v for conducting tracks of width b and its compensation k;
FIG. 10 shows a representation of the phase-frequency characteristic for an uncompensated structure (k=0 μm) according to FIG. 9a and for a compensated structure (k=0μm) according to FIG. 9b;
FIG. 11 shows a schematic representation in cross-section to illustrate the compensation k for layer offset v for coil-like structures;
FIGS. 12
a and 12b show examples of inductive coupling in an embodiment of the invention;
FIG. 13 shows an embodiment of an integrated bandpass filter with two resonators according to the embodiment in FIG. 2 and a coupling according to FIG. 12a.
The resonator shown in FIG. 1 comprises two conducting track sections 10, 12, which oppose each other. In their overlap region, in the actual design there is arranged a thin dielectric layer, although this is not shown in FIG. 1. The larger the dielectric constant is, the smaller the resonator may be built. The dielectric constant ε is therefore preferably larger than 5. Actual embodiments also include materials with dielectric constants ε>17 or even materials with a dielectric constant ε>70. The thickness d of the dielectric layer is smaller than half the width b of a conducting track member 10 or 12. The beginning 16 of the conducting track member 12 is connected to ground, as is the end 18 of the conducting track member 10.
A resonator according to a further embodiment of the invention is shown in FIG. 2. Here, the conducting track structures 20, 22 are designed spiral-shaped, the beginning 24 and the end 26 are linked to each other via a coupling member 28, so that they are at the same, floating potential.
Both with the embodiment according to FIG. 1 and also the embodiment according to FIG. 2, resonators may be realized in a multilayer substrate that are substantially smaller than a quarter wavelength and in which inductance and capacitance are not spatially separated.
FIGS. 3
a and 3b show examples of multilayer structures for resonators according to FIG. 1 or FIG. 2. Again, the dielectric layers are left out between the individual layers. Either similar or different resonator types may be combined in a layered structure.
FIG. 4 shows a bandpass filter made up from two resonators 40, 42 according to FIG. 1. The resonators 40, 42 are attached to earth 44 with their electrically remote ends. A coupling capacitor 46 provides for a further reduction of the resonant frequency of the filter and, together with the inductive coupling through the conducting track members 41 running parallel, an additional zero point in the transmission function. The input or output of signals takes place via connecting members 48, 50 directly connected to the conducting track structures. FIG. 4 also shows an example of a layered structure. The dielectric layer 52 of the filter is 25 μm thick and comprises a material with a dielectric constant ε of 18. The dielectric layers 54 surrounding the filter each have a thickness of 100 μm and comprise a material with a dielectric constant of 7.5. Earthing surfaces 56 complete the symmetrical structure.
FIG. 5 shows the transmission characteristic S21 of the filter in FIG. 4. The stop band lies below 2 GHz and good transmission behavior is achieved in the 5 GHz region. In practice, the dimensions of the filter are approximately 1×1 mm2.
FIG. 6 shows a balancing transformer made from a resonator according to FIG. 1. The input of the differential signals takes place symmetrically by means of the connectors 64 of the conducting track structure 60 or 66 of the conducting track structure 62. The output takes place asymmetrically via the connector 68 on the conducting track structure 60. The ends 72 and 74 of the conducting track structures 60 or 62 are connected to earth 70. The layer sequence of the substrate is as in FIG. 4. For the sake of clarity, the drawing has been elongated in the vertical direction.
It is particularly space-saving if the filter is used simultaneously as a balancing transformer and adaptor network. FIG. 7 shows an example of a combined filter, balancing and adaptor network with two resonators 80 and 82 designed according to the principle shown in FIG. 2. Coupling with the first resonator 80 takes place symmetrically via the connectors 84, 86. The output takes place asymmetrically via the connecting member 88. The impedance of the symmetrical connecting members 84, 86 and of the asymmetrical connecting member 88 may be amended by suitable selection of the position of the taps on each resonator 80 or 82. If greater stop band attenuation or steeper flanks are desired than in the spectrum shown in FIG. 8, further resonators may be connected in. The coupling of the resonators 80, 82 is incidentally amplified via a contact bridge 90, as described in greater detail in connection with FIG. 12a.
Since, dependent upon manufacturing, the metal layers of the conducting track structures are not perfectly aligned one over the other, variations in the distributed capacitance and inductance of the conducting tracks is to be expected. FIG. 9a shows an uncompensated structure in which two conducting tracks are arranged with an offset v above and below a dielectric layer of thickness d. The effects of this unwanted offset v on the resonant frequency may be compensated for with a conducting track of width 2k, as shown in FIG. 9b, where k is chosen to be approximately equal to the maximum position offset v plus half the layer thickness d of the dielectric layer. The effects of the position offset on an arrangement with two b=450 μm-wide conducting tracks for a layer sequence shown in FIG. 4 with d=25 μm are shown in FIG. 10. The dashed curves are the results for the uncompensated structure with k=0 μm according to FIG. 9a and the continuous curves are the results for a compensated structure with k=50 μm according to FIG. 9b.
For multilayer, coil-like conducting tracks, the arrangement according to FIG. 11 offers advantages because it may be designed in a more space-saving manner compared with the compensation according to FIG. 9b. If what is important is only a precise inductance at low frequencies, then the approximation given above for k may be used. For precise adjustment of the resonant frequency, a compensation k of the size of the maximum layer offset v is suitable. If earth surfaces are brought close to the conducting tracks, the compensation may even be chosen to be smaller than v. In FIG. 11, because of production variability, the lower two conducting tracks are offset by a value v to the right. To compensate, on the upper layer, the neighboring conducting tracks are moved further apart by an amount k. The distributed capacitance and inductance are reduced in the conducting track pair at left in FIG. 11, but the opposite conditions apply in the conducting track pair at right, so that the resonant frequency remains constant overall. The proposed resonators are also less sensitive to variations in the width of the conducting tracks. If the conducting track width increases, the capacitance also increases, but the decreasing inductance compensates for this effect in part. The higher the ratio of the width of the conducting track to the separation from the earth surfaces, the less the resonant frequency changes.
FIGS. 12
a and 12b show simple measures as to how the coupling between conducting track structures may be strengthened. The bridge 90 in FIG. 12a and the common conducting track member 92 in FIG. 12b act like an amplified magnetic coupling between the conducting track members 93 and 94 or 95 and 96. A simple adjustment of the coupling strength may be achieved by displacing the bridge without having greatly to change the remainder of the circuit. Given identical coupling, the conductors according to FIG. 12a or FIG. 12b may therefore have larger separations or be shorter. In the case of small separations, the coupling depends, according to the prior art, very strongly on the precision during production, whilst the position of a bridge may be very precisely specified. In the case of longer conducting track structures also, which may not be regarded as more than coils, the magnetic coupling is increased if, close to the foot, a bridge 90 or a common conducting track member 92 is introduced. This is particularly meaningful for broadband applications or for applications on thin substrates.
The bandpass filter illustrated in FIG. 13 is formed by two resonators 110, 112 according to FIG. 2, which are compensated according to FIG. 11 against offsets and are connected to earth 115 at their end. The conducing track member 114 amplifies the magnetic coupling between the parallel-arranged conducting tracks 113. In addition, the capacitor 118 couples the resonators. The coupling of the infeed lines 122, 124 to the resonators takes place capacitively 116 and directly. The conductor structure 120 forms an end capacitor linked to earth, which reduces the resonant frequency.
Patent Application
20080048797
