Micro-acoustic filter having compensated cross-talk and method for compensation

Patent metadata

Field	Value
Publication number	US-9362884-B2
Application number	US-201113576653-A
Country	US
Kind code	B2
Filing date	Feb 14, 2011
Priority date	Feb 22, 2010
Publication date	Jun 7, 2016
Grant date	Jun 7, 2016

Abstract

The invention relates to a micro-acoustic filter having a first and a second converter, in which the electromagnetic and capacitive cross-talk between the first and second converters is compensated for by providing additional coupling capacitors and additional current loops. Additional coupling capacitors and current loops are arranged in such a manner that they can counteract the sign of the natural coupling specified by the design and thus completely compensate for said coupling.

First claim

The invention claimed is:

1. A micro-acoustic filter comprising:
a first and a second transducer, which are realized on a common piezoelectric substrate,
wherein the first transducer and the second transducer each have two connection pads; and
a coupling line, which connects a first connection pad of the first transducer to a coupling pad,
wherein the coupling pad is embodied as a metal area and is arranged in the vicinity of that connection pad of the second transducer which is at the greater distance from the first connection pad of the first transducer,
wherein, in at least one of the transducers, the current path to this transducer, comprising the current feeds to the connection pads, the connection pads themselves and that portion of the current path which runs via the acoustic system, forms at least one crossover, such that a complete first loop and at least one part of a second loop are formed in the imaginary geometrical projection of the current path onto the substrate plane,
wherein the current path to or through the other one of the transducers forms a third loop,
wherein a respective inductive coupling takes place between the first and third and between the second and third loops, and
wherein the areas enclosed by first and second loops and projected onto the substrate are in a ratio to one another such that the two inductive couplings mutually compensate for one another.

2. The filter according to claim 1 ,
wherein the first and second transducers are separated by a shielding structure, which is connected to ground via at least one connection pad, and
wherein the shielding structure comprises metallic strips, which either
are guided transversely via an acoustic track of a filter embodied as an SAW filter, the first and second transducers that couple to one another being arranged in said track, or
are arranged between the connection pads or electrodes of the first and second transducers that couple to one another.

3. The filter according to claim 2 , wherein a connection pad of the shielding structure is guided at least partly around an adjacent connection pad of one of the transducers.

4. The filter according to claim 1 , wherein the coupling line either is embodied as a metallic conductor section running on the substrate, or is embodied as a bonding wire or other conductor section arranged not directly on, but rather above or below the substrate.

5. The filter according to claim 1 , wherein in the at least one of the transducers in which the current path forms the complete first loop and the at least one part of the second loop, inductively generated electromagnetic fields in the first loop and the second loop are oppositely polarized.

6. The filter according to claim 1 ,
wherein the filter comprises a chip formed from the material of the substrate,
wherein the chip is mounted on a housing lower part or a carrier substrate,
wherein the connection pads on the chip are connected to external connections at the underside of the housing lower part or of the carrier substrate by means of bonding wires via connection areas on the housing lower part or on the carrier substrate, and
wherein the current paths shaped to form loops at least partly comprise the bonding wires.

7. The filter according to claim 1 ,
wherein the filter comprises a chip formed from the material of the substrate,
wherein the chip is mounted by means of flip-chip connections on a housing lower part or a carrier substrate, and
wherein one of the loops is formed by the connection pads, that portion of the current path which runs via the acoustic system, the flip-chip connections and conductor sections arranged on the housing lower part or the carrier substrate.

8. The filter according to claim 1 , embodied as an SAW filter,
wherein at least one of the transducers is cascaded,
wherein the cascading is different in at least two longitudinal sections of the transducer, and
wherein that section of the current path which is formed by the acoustic system runs substantially transversely through that longitudinal section of the transducer which has the smallest degree of cascading.

9. A method for reducing cross-talk in a micro-acoustic filter, the filter comprising
a first and a second transducer, which are realized on a common piezoelectric substrate,
wherein the first transducer and the second transducer each have two connection pads, and
a coupling line, which connects a first connection pad of the first transducer to a coupling pad,
wherein the coupling pad is embodied as a metal area and is arranged in the vicinity of that connection pad of the second transducer which is at the greater distance from the first connection pad of the first transducer, the method comprising:
varying the size of the coupling pad and/or the distance thereof from the more distant connection pad of the second transducer until optimum decoupling to is achieved;
a) providing the coupling pad with a sufficient size;
b) determining filter properties suitable for determining the coupling;
c) reducing the area of the metallic coupling pad by material removal by a relatively small amount relative to the size of the coupling pad;
d) determining at least one of the filter properties anew;
e) determining whether said at least one of the filter properties has changed positively by comparison with the determination in method step b), and repeating steps c) and d) in the case of an improvement being determined.

10. The method according to claim 9 , with method step b) further comprising:
determining the transfer function of the filter; and
using the suppression in a given stop band as a measure of the coupling.

11. The method according to claim 9 , further comprising:
in method steps b) and d), determining the transfer function of the filter and determining the number of phase changes of the transfer function in a given frequency range all around a passband of the filter as a measure of the coupling,
wherein method step e) involves checking whether an increase in the number of phase changes has taken place, and
wherein an increase is evaluated as improved decoupling.

Assignees

• Moreno Granado Guillermo
• Kiwitt Jürgen
• Pitschi Maximilian
• Gärtner Tilo
• Epcos Ag

Inventors

• Moreno Granado Guillermo
• Kiwitt Jürgen
• Pitschi Maximilian
• Gärtner Tilo

Classifications

• H03H9/02913 Primary

  Measures for shielding against electromagnetic fields (shielding of electrical components in general H05K9/00) · CPC title

• H03H9/02874 Primary

  of direct coupling between input and output transducers · CPC title

• H03H9/02952

  of parasitic capacitance · CPC title

• H03H9/02992

  Details of bus bars, contact pads or other electrical connections for finger electrodes · CPC title

• H03H9/6493

  Side lobe suppression · CPC title