Wave transmission lines and networks – Coupling networks – Electromechanical filter
Patent
1999-03-12
2000-12-19
Pascal, Robert
Wave transmission lines and networks
Coupling networks
Electromechanical filter
333196, 310313D, H03H 964
Patent
active
061632368
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
Longitudinal mode resonator filters, also called dual mode filters or DMS filters, are referred to below as surface wave filters referenced OFW filters that comprise two normal finger transducers arranged within reflectors according to the schematic plan view according to FIG. 1 and that are effective as input or, respectively, output transducer 2, 12. They have two-pole filter characteristics. When two DMS tracks A and B that are frequency-shifted relative to one another such that the high-frequency resonance of the low-frequency track B falls onto the low-frequency resonance of the high-frequency track A are interconnected as shown in FIG. 1, then what is referred to as a twin dual mode filter is obtained, this being distinguished by three-pole filter characteristics and by an enhanced edge steepness compared to the single track.
Given the filter structure according to FIG. 1, a respective bond wire at the side of the filter input and filter output IN or, respectively, OUT must be conducted at least across one connecting line, across one of the DMS tracks A, B in the worst case. This requires additional chip or, respectively, substrate area for the bond pads 5 connected to the transducers 2, 12 via interconnects 4 between the DMS tracks A, B and complicates the fabrication of such a filter.
It is also disadvantageous that the impedances of the filter can be made arbitrarily smaller by enlarging the aperture since disturbing transverse modes occur in this case.
Given symmetrical operation of the twin dual mode filter, over and above this, no optimum suppression of the electrical crosstalk is achieved since the geometry is not symmetrical.
When the DMS tracks are not optimally aligned relative to one another with respect to the resonant frequencies, then increased amplitude and group running time distortions occur in the filter transmission band. Such a de-adjustment is unavoidable in mass production due to the scatters of the manufacturing parameters and the inhomogeneities on the wafer.
SUMMARY OF THE INVENTION
The present invention is based on the object of specifying a twin dual mode filter according to the species initially sited wherein at least the first-cited problem is solved, i.e. a crossing-free layout is created for the bond wires.
In general terms the present invention is a twin dual mode filter, having two interconnected DMS filters with two normal finger transducers as input or, respectively, output transducers per DMS track within reflectors. The DMS tracks are frequency-shifted relative to one another such that the high-frequency resonance of the low-frequency track falls onto the low-frequency resonance of the high-frequency track. Two reflectors respectively interconnected with one of the transducers are arranged between input and output transducers of each DMS track. The reflectors of the input or, respectively, output side are respectively electrically connected to one another via interconnects.
Advantageous developments of the present invention are as follows.
The reflectors are replaced by fingers having a suitable width.
Two twin dual mode filters are connected in parallel.
Two twin dual mode filters have series-connected outputs.
Two twin dual mode filters have inputs connected in series and outputs connected parallel.
Ohmic resistors are connected into the leads to the input and output transducers.
Two reflectors respectively interconnected with one of the transducers and having fingers inclined relative to the propagation direction of the surface waves are arranged between input and output transducers of the low-frequency DMS track.
Terminal elements of the filter input and filter output are applied intersection-free onto the substrate surfaces of the DMS tracks facing away from one another.
BRIEF DESCRIPTION OF THE DRAWINGS
The features of the present invention which are believed to be novel, are set forth with particularity in the appended claims. The invention, together with further objects and advantages, may best be understood by reference
REFERENCES:
patent: 6060964 (2000-05-01), Baier et al.
Pascal Robert
Siemens Matsushita Components GmbH & Co.
Summons Barbara
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