Hybrid SAW-BAW Multiplexer for Low Second Harmonic Distortion

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Solution Overview

Problem

Existing acoustic wave filters, particularly those using bulk acoustic wave (BAW) resonators, face challenges in achieving low second harmonic distortion, which is becoming increasingly demanding in certain applications such as 5G New Radio (NR) systems.

Innovation Solution

The proposed solution involves a multiplexer design that includes a receive filter with a shunt surface acoustic wave (SAW) resonator and a plurality of bulk acoustic wave (BAW) resonators. The shunt SAW resonator has a resonant frequency within the transmit passband, which helps reduce second harmonic distortion at the common node.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If bulk acoustic wave (BAW) resonators are used in acoustic wave filters, then the filters can achieve good passband characteristics, but the second harmonic distortion becomes excessively high

Engineering Contradiction:

Improvesecond harmonic distortionVSAvoidlinearity performance

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent combines surface acoustic wave (SAW) resonators and bulk acoustic wave (BAW) resonators into a hybrid filter structure. The SAW resonators are positioned to provide shunt paths that cancel the second harmonic distortion generated by the BAW resonators, while the BAW resonators maintain the desired passband characteristics. This merging of different resonator types resolves the contradiction between achieving low second harmonic distortion and maintaining good linearity performance.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The SAW resonators act as intermediary elements that mediate the harmful second harmonic distortion produced by the BAW resonators. By introducing these intermediate SAW resonators with specific resonant frequencies, the patent creates a mechanism to suppress the distortion without directly modifying the BAW resonator structure, thus preserving the passband characteristics while improving linearity.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Adaptability or versatility

If multiple filters are arranged in a multiplexer to handle different frequency bands, then the system can support multiple communication standards, but the second harmonic distortion from one filter affects the performance of other filters

Engineering Contradiction:

Improvemulti-band supportVSAvoidinter-filter interference

Core Design Contradiction:

Adaptability or versatilityVSObject-generated harmful factors

Solution Approach 1:

The patent converts the harmful second harmonic distortion generated by the receive filter into a beneficial effect by strategically positioning SAW resonators whose resonant frequencies coincide with the transmit filter's passband. The distortion energy is redirected to create transmission zeros that improve the transmit filter's rejection of spurious signals, thus transforming inter-filter interference into a performance enhancement.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent applies preliminary anti-action by designing the SAW resonator frequencies to preemptively counteract the second harmonic distortion before it can interfere with the transmit filter performance. The shunt SAW resonators are configured to create transmission zeros at specific frequencies, proactively preventing the distortion from degrading the overall multiplexer performance.

Inventive Principle:

Principle #9Preliminary anti-action

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

This design effectively reduces second harmonic distortion in the transmit filter, improving the linearity and meeting the stringent specifications of 5G NR applications while maintaining low insertion loss in the receive passband.

Implementation Method 1

A surface acoustic wave resonator can include an interdigital transductor electrode on a piezoelectric substrate. The surface acoustic wave resonator can generate a surface acoustic wave on a surface of the piezoelectric layer on which the interdigital transductor electrode is disposed.

Methodology Applied

Scientific EffectSurface acoustic wave: Surface Acoustic Wave

Implementation Method 2

A surface acoustic wave resonator can include an interdigital transductor electrode on a piezoelectric substrate

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 3

In BAW resonators, acoustic waves propagate in a bulk of a piezoelectric layer

Methodology Applied

Scientific EffectBulk acoustic wave: Surface Acoustic Wave

Data Source

PatentUS12244294B2Multiplexer with acoustic wave filter including different types of resonators

Publication Date: 2025.03.04 SKYWORKS SOLUTIONS INC

AI summary

Aspects of this disclosure relate to multiplexers with that include an acoustic wave resonator. The acoustic wave filter includes a plurality of acoustic wave resonators of a first type and a shunt acoustic wave resonator of a second type. The shunt acoustic wave resonator of the second type has lower second harmonic distortion than the acoustic wave resonators of the first type. The shunt acoustic wave resonator of the second type has a resonant frequency in a passband of another filter of the multiplexer. Related radio frequency modules, wireless communication devices, and methods are also disclosed.