XBAR Matrix Filters With Built-In RF Impedance Matching

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Solution Overview

Problem

Current RF filters, particularly those using acoustic wave resonators, are not well-suited for higher frequencies and wider bandwidths required by future communication networks, such as the 5G NR standard, which includes bands like N77, N79, and millimeter wave frequencies, necessitating improved filtering capabilities.

Innovation Solution

The development of Transversely-Excited Film Bulk Acoustic Resonator (XBAR) matrix filters with impedance matching to radio frequency front-end (RFFE) elements, allowing for noncontiguous passbands and eliminating the need for external impedance matching or switching, utilizing XBAR resonators with interleaved fingers on a piezoelectric diaphragm for high electromechanical coupling and frequency capability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If traditional acoustic wave resonators are used for RF filtering, then filtering functionality is provided, but they are not well-suited for higher frequencies and wider bandwidths required by future communication networks

Engineering Contradiction:

Improvefrequency capabilityVSAvoidsuitability for future communication networks

Core Design Contradiction:

SpeedVSReliability

Solution Approach 1:

The patent changes the fundamental operating parameters of the resonator by transitioning from surface acoustic wave (SAW) or bulk acoustic wave (BAW) modes to transverse electric (TE) mode resonators. This parameter change enables operation at higher frequencies (millimeter wave bands) and provides wider bandwidth capability, making the filter suitable for future communication networks while maintaining filtering functionality

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces traditional mechanical acoustic wave resonators (SAW/BAW) with a resonator structure that uses transverse electric mode operation. This substitution fundamentally changes the physical mechanism from mechanical acoustic waves to electromagnetic resonance in TE mode, enabling higher frequency operation and improved bandwidth performance

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Ease of operation

If impedance matching components are added to match filter impedances to RFFE elements, then impedance matching is improved, but device complexity and number of external components increase

Engineering Contradiction:

Improveimpedance matchingVSAvoidnumber of external components

Core Design Contradiction:

Ease of operationVSDevice complexity

Solution Approach 1:

The filter design incorporates built-in impedance matching capabilities through its internal resonator structure and circuit topology. The TE mode resonators and filter architecture are designed to naturally present matched impedances to standard RFFE elements (power amplifiers, low noise amplifiers, antennas), eliminating the need for external impedance matching components and reducing overall device complexity

Inventive Principle:

Principle #25Self-service

3Adaptability or versatility

If switches are added for impedance switching between different RFFE elements, then adaptability is improved, but device complexity and potential noise figure increase

Engineering Contradiction:

Improveimpedance switching capabilityVSAvoidswitching components

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The filter is designed with universal impedance characteristics that work with multiple different RFFE elements simultaneously. The TE mode resonators and filter topology provide broadband impedance matching that accommodates various power amplifiers, low noise amplifiers, and antennas without requiring switching mechanisms, thereby reducing device complexity and potential noise figure while maintaining adaptability

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 XBAR matrix filters provide enhanced performance by achieving high-frequency filtering with noncontiguous passbands, reducing the need for external components, and minimizing noise figure, thus supporting advanced communication standards like 5G NR with improved size, cost, and reliability.

Implementation Method 1

An interdigital transducer (IDT) is formed on opposing surfaces of the piezoelectric material

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

A plurality of acoustic wave resonators are formed on the piezoelectric material

Methodology Applied

Scientific EffectAcoustic wave resonance: Resonance

Data Source

PatentUS11929733B2Transversely-excited film bulk acoustic resonator matrix filters with input and output impedances matched to radio frequency front end elements

Publication Date: 2024.03.12 MURATA MFG CO LTD

AI summary

There are disclosed matrix filters having an antenna port, receive ports and transmit ports. A receive matrix filter is coupled between each receive port and the antenna port; an a transmit matrix filter is coupled between the antenna port and each transmit port. An impedance at the receive port is matched to an input impedance of a low noise amplifier (LNA), an impedance at the transmit port is match to an output impedance of a power amplifier (PA), and an impedance at the antenna port is match an impedance of an antenna.