Acoustic Wave Filter Matching Network With Shared RF Terminal
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Solution Overview
Problem
Existing multi-band communication devices face complexity and cost issues due to the need for numerous matching components and long, lossy transmission lines when connecting RF filters to an antenna, particularly in designs employing bulk acoustic wave (BAW), surface acoustic wave (SAW), and thin film bulk acoustic resonator (FBAR) filters.
Innovation Solution
A radio frequency (RF) signal processing device with a common terminal and a plurality of matching capacitors, where each filter is connected either directly to the common terminal or a corresponding matching capacitor, with an inductor or transmission line connected between the common terminal and ground, simplifying the matching network and reducing component count.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional series and shunt transmission lines are used for matching multiple filters, then frequency band matching can be achieved, but the number of components increases and transmission lines become long and lossy
Solution Approach 1:
The patent combines multiple matching functions into a single parallel circuit configuration. Instead of using separate series and shunt transmission lines for each filter, the invention uses one parallel transmission line with multiple capacitive coupling points, where each coupling point connects to a different filter. This merging approach reduces the total number of components while maintaining the ability to match multiple frequency bands simultaneously.
Solution Approach 2:
The single parallel transmission line structure serves multiple functions: it provides impedance matching for multiple filters across different frequency bands, acts as a common ground reference, and enables selective coupling to different filters through the capacitive networks. Each capacitive coupling point can be independently tuned to match a specific filter's frequency characteristics, making the structure universally applicable to multi-band filter systems.
2Reliability
If multiple transmission lines are used to isolate components, then frequency band separation is achieved, but four-layer PCB is required increasing cost and complexity
Solution Approach 1:
The patent merges the isolation function previously requiring separate transmission lines into the single parallel transmission line structure. The capacitive coupling networks provide electrical isolation between different frequency band paths while maintaining a common ground reference, eliminating the need for additional isolation transmission lines and reducing PCB layer requirements.
Solution Approach 2:
The capacitive coupling networks act as intermediary elements between the parallel transmission line and the filters. These capacitors provide frequency-selective coupling while maintaining galvanic isolation between different frequency bands, allowing multiple filters to share a common ground reference without interfering with each other's performance.
3Reliability
If empirical design with RF simulator is used to optimize component values, then best performance can be achieved, but too many matching components are used and results are not guaranteed
Solution Approach 1:
The patent changes the fundamental parameters of the matching network topology from series/shunt transmission lines to a parallel transmission line with capacitive coupling. This parameter change simplifies the design space, reducing the number of variables that need to be optimized through empirical simulation. The design now primarily involves selecting capacitor values and coupling points rather than optimizing multiple transmission line lengths and component values.
Data Source
AI summary
A method and circuit matches a device to n filters, wherein each filter is a SAW filter, BAW filter, or FBAR filter. The method and system: (a) provide an inductor or transmission line connected between a common terminal and ground; (b) provide a plurality of capacitance values (C1m, C2m, . . . , Cnm) each corresponding to one of the n filters; and (c) for each of the n filters, directly connect a first terminal of the filter to either: (1) the common terminal, or (2) a first terminal of a corresponding capacitor having the correspondence capacitance value calculated in step (b), where a second terminal of the corresponding capacitor is directly connected to the common terminal.