# US 2022/0045663 A1 · Acoustic filter with improved reflectivity

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- Number: US 2022/0045663 A1
- Document ID: US20220045663A1
- Status: Published application
- Kind: A1
- Application number: 17/297,906
- Filed: 2019-12-13
- Published: 2022-02-10
- Earliest claimed: 2018-12-19
- Assignees: Rf360 Europe GmbH
- Applicants: Rf360 Europe GmbH
- Inventors: Simone COLASANTI; Samir TAZARINE; Robert KOCH; Franz KUBAT
- Web page: https://patentgrep.com/patent/US20220045663A1

## CPC

- H03H 9/542: {including passive elements (H03H9/545 takes precedence)}
- H03H 7/463: {Duplexers}
- H03H 9/02102: {of temperature influence (cutting angles H03H9/02015)}
- H03H 9/02834: {of temperature influence (cut angles H03H9/02543)}
- H03H 9/17: having a single resonator (crystal tuning forks H03H9/21)
- H03H 9/568: {consisting of a ladder configuration}
- H03H 9/605: {consisting of a ladder configuration}
- H03H 9/6483: {Ladder SAW filters}
- H03H 9/6493: {Side lobe suppression}
- H03H 9/706: {Duplexers}
- H03H 9/725: {Duplexers}
- H03H: IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS (waveguides, resonators, lines or other devices of the waveguide type H01P)

## Abstract

A filter circuit comprises a main operating unit (MU) arranged in the series signal line providing most of the filter function of the filter circuit. A micro acoustic last series resonator (RLs) as a last element of the main operating unit in the series signal line is prone to excite a spurious mode that is damped with a final series capacitance (CEs) circuited between the last element and the antenna terminal (AT).

## Claims

### Claim 1

A filter circuit that provides a pass band, comprising:
a series signal line (SLS) that connects a first terminal (T1) and an antenna terminal (AT);
a main operating unit (MU) arranged in the series signal line providing most of the filter function of the filter circuit;
a micro acoustic last series resonator (RSL) that is a last element in the series signal line and part of the main operating unit; and
a final series capacitance (CES) circuited between the last element and the antenna terminal.

### Claim 2 (depends on 1)

The filter circuit of claim 1,
wherein the filter circuit is formed on a substrate, and
wherein the final series capacitance is embodied as an external discrete element or as an integrated capacitance on the substrate or is a resonator acting with its static capacitance only and having a resonance frequency outside the pass band.

### Claim 3 (depends on 1)

The filter circuit of claim 1,
wherein a further node (N) is arranged in the series signal line between the last element and the final series capacitance, and
wherein a further parallel branch is circuited between the further node and a ground terminal, the further parallel branch comprising an impedance element (IE) chosen from a further parallel resonator, a parallel coil and a parallel capacitance.

### Claim 4 (depends on 1)

The filter circuit of claim 1,
wherein an additional parallel capacitance (CPA) is arranged in the further parallel branch, and
wherein an additional series coil (ISA) is circuited in parallel to the final series capacitance (CES).

### Claim 5 (depends on 1)

The filter circuit of claim 1,
wherein a phase shifting circuit is circuited between the main operating unit (MU) and the antenna terminal, the phase shifting circuit comprising the last series resonator, an additional parallel coil (IPA) arranged in the last parallel branch and the final series capacitance in the series signal line.

### Claim 6 (depends on 1)

The filter circuit claim 1,
wherein the main operating unit ends with a last node and a last parallel branch is connected to the last node, and a parallel micro-acoustic resonator is arranged in the parallel branch, and
wherein said last node is directly connected to the final series capacitance and the final series capacitance is directly connected to the antenna terminal.

### Claim 7 (depends on 1)

The filter circuit of claim 1,
wherein the main operating unit comprises a ladder type arrangement of series and parallel resonators.

### Claim 8 (depends on 1)

The filter circuit of claim 1,
wherein the resonators of the ladder type arrangement comprise SAW or BAW resonators.

### Claim 9 (depends on 1)

The filter circuit of claim 1,
wherein the main operating unit comprises a DMS filter series-connected to a micro-acoustic series resonator.

### Claim 10 (depends on 1)

The filter circuit of claim 1,
wherein the last series resonator is a temperature compensated thin film SAW resonator or a BAW resonator.

### Claim 11 (depends on 1)

The filter circuit of claim 1,
wherein a first operating unit comprising the filter circuit and a second micro-acoustically operating unit chosen from a passband filter circuit or a notch-filter are connected to the same antenna terminal in a permanent or switchable form,
wherein the first or the second operating unit comprises a micro acoustic resonator next to the antenna terminal,
wherein this resonator next to the antenna terminal is prone to produce a spurious mode in the operating frequency band of the respective other unit, and
wherein the final series capacitance suppresses this spurious mode.