RF Filter Ground Layout for Adjacent-Channel Suppression
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Solution Overview
Problem
Existing RF filters face challenges in achieving good adjacent-band suppression and power durability while minimizing insertion loss and maintaining a steep edge in their passband, particularly in miniaturized terminal devices.
Innovation Solution
A RF filter design comprising a reactance filter sub-filter with two parallel resonators and one series resonator, combined with a DMS filter sub-filter, where the ground terminals of the first parallel resonator and the second sub-filter are separated and connected to external housing contacts to reduce galvanic coupling, and the filter is constructed on a common piezoelectric substrate with optimized housing and metallization to enhance power durability and adjacent-band suppression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a reactance filter is used to achieve good adjacent-band suppression, then the suppression performance is improved, but the insertion loss increases and power durability deteriorates
Solution Approach 1:
The filter is divided into two separate sub-filters (reactance filter and DMS filter) that are connected in series. Each sub-filter performs a specific function: the reactance filter provides adjacent-band suppression while the DMS filter provides low insertion loss. This segmentation allows each part to be optimized for its specific purpose without compromising the other.
Solution Approach 2:
The patent combines two different filter technologies (reactance filter and DMS filter) into a single hybrid filter structure. By merging the strengths of both filter types, the overall filter achieves both good adjacent-band suppression and low insertion loss, which neither filter type could achieve alone.
2Device complexity
If ground terminals are connected together to simplify the structure, then the device complexity is reduced, but galvanic coupling causes undesirable signals and falsifies the useful signal
Solution Approach 1:
The ground terminals of the two sub-filters are separated into distinct ground connections rather than being connected together. This segmentation prevents galvanic coupling between the sub-filters, eliminating the harmful signals that would otherwise be generated. Each sub-filter has its own independent ground path to the housing.
Solution Approach 2:
The housing serves as an intermediary ground connection point for the two sub-filters. By using the housing as a common ground reference rather than directly connecting the ground terminals, the patent eliminates galvanic coupling while still providing a common reference potential. The housing acts as a mediator that prevents direct electrical coupling between the sub-filters.
3Loss of energy
If a DMS filter is used to achieve low insertion loss, then the power efficiency is improved, but the adjacent-band suppression is insufficient
Solution Approach 1:
The filter functionality is segmented into two specialized sub-filters: the DMS filter handles the low insertion loss requirement while the reactance filter handles the adjacent-band suppression requirement. This segmentation allows each sub-filter to be optimized for its specific function without compromise.
Solution Approach 2:
The patent merges the DMS filter and reactance filter in a series configuration, combining their complementary strengths. The DMS filter provides low insertion loss in the passband while the reactance filter provides sharp adjacent-band suppression, achieving overall performance that exceeds either filter type alone.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The combined filter achieves improved adjacent-band suppression, high edge steepness, and power durability by leveraging the strengths of reactance and DMS filters, with reduced insertion loss and minimized galvanic coupling, leading to better performance in suppressing unwanted frequencies and maintaining signal integrity.
Implementation Method 1
The first and second sub-filters can be constructed on a common piezoelectric substrate and connected to one another there
Implementation Method 2
SAW or surface wave elements, which are distinguished by a small size and a great variety with respect to the electrical parameters that can be adjusted, are particularly preferred
Implementation Method 3
RF filters constructed on the basis of bulk acoustic wave resonators or surface acoustic wave elements offer good electrical properties
Data Source
AI summary
The invention relates to a filter with a first partial filter (TF1), comprising a series resonator (S1) and at least two parallel resonators (P1, P2) that are arranged in respective parallel branches, and with a second partial filter (TF2) configured as a DMS filter. The filter also comprises a housing with a plurality of internal housing contacts (GKi) on a base plate that are connected to terminal areas on the substrate (SU) and external housing contacts (GKa), fewer than the internal contacts, that are connected to the internal housing contacts (GKi) via lines (DL1, DL2) guided within the base plate. At least two lines for connections to ground of the first parallel resonator (P1) and the second partial filter (TF2) are guided separately in or on the base plate and are connected to at least two different external housing contacts (E4, E2).