Ladder-Type SAW Duplexer Electrode Ratios for Low Loss and Isolation

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Solution Overview

Problem

Ladder-type SAW devices for duplexers face challenges in achieving low loss and high isolation while being miniaturized, as existing designs either increase insertion loss or reduce isolation due to electrode finger ratios and spacing, which affect static capacitance and parasitic capacitance.

Innovation Solution

The SAW device is configured with specific electrode finger ratios (LT/PT) for transmission and (LR/PR) for receiving, where (LT/PT) < (LR/PR), to reduce static capacitance in transmission and increase parasitic capacitance in receiving, thereby achieving low insertion loss and high isolation without increasing substrate size.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If the ratio L/P of electrode finger width to pitch is set to more than 0.5 to improve formation process precision, then manufacturing precision is improved, but the spacing between electrode fingers is narrowed, increasing static capacitance and insertion loss

Engineering Contradiction:

Improveprecision of formation processVSAvoidinsertion loss

Core Design Contradiction:

Manufacturing precisionVSLoss of energy

Solution Approach 1:

The patent applies different L/P ratios to different functional blocks: the transmission SAW device uses L/P > 0.5 for manufacturing precision, while the receiving SAW device uses L/P < 0.5 to reduce static capacitance and improve isolation. This local differentiation resolves the contradiction by optimizing each block for its specific function rather than using a uniform design.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The duplexer is segmented into separate transmission and receiving SAW devices, each with independently optimized electrode finger ratios. This segmentation allows the transmission path to prioritize low loss while the receiving path prioritizes isolation, resolving the contradiction through functional separation.

Inventive Principle:

Principle #1Segmentation

2Reliability

If the ratio L/P of electrode finger width to pitch is set to less than 0.5 to improve attenuation characteristics, then isolation is improved, but the spacing between electrode fingers is widened, reducing static capacitance and increasing insertion loss

Engineering Contradiction:

Improveisolation characteristicsVSAvoidinsertion loss

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

Inventive Principle:

Principle #3Local quality

3Reliability

If the number of pairs of electrode fingers and cross width are increased to reduce insertion loss and improve attenuation characteristics, then transmission and isolation are improved, but the size of the SAW resonator increases

Engineering Contradiction:

Improveattenuation characteristicsVSAvoidsize of SAW resonator

Core Design Contradiction:

ReliabilityVSArea of moving object

Solution Approach 1:

The patent changes the L/P ratio parameter to optimize performance without increasing size. By adjusting the electrode finger width relative to pitch, the patent achieves improved isolation and attenuation characteristics while maintaining compact resonator dimensions, avoiding the need to increase the number of electrode finger pairs or cross width.

Inventive Principle:

Principle #35Parameter changes

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 configuration results in a SAW device with reduced transmission signal attenuation, enabling low power consumption and high-quality communication with minimal receiving noise, suitable for small-sized duplexers and communications equipment.

Implementation Method 1

a plurality of SAW resonators for transmission connected in series with a transmission signal line and a plurality of SAW resonators for transmission connected in parallel with the transmission signal line; and a plurality of SAW resonators for receiving connected in series with a receiving signal line and a plurality of SAW resonators for receiving connected in parallel with the receiving signal line

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

SAW device formed on a main surface or main surfaces of one or a plurality of piezoelectric substrates, comprising a ladder-type transmission SAW device

Methodology Applied

Scientific EffectSurface acoustic wave propagation: Surface Acoustic Wave

Data Source

PatentUS7456705B2Surface acoustic wave device, duplexer, and communications equipment

Publication Date: 2008.11.25 KYOCERA CORP

AI summary

A SAW device D1 according to the present invention comprises a ladder-type SAW device T1 for transmission and a ladder-type SAW device R2 for receiving on a main surface of a piezoelectric substrate. The ratio (LT/PT) of the width LT of electrode fingers to the pitch PT between the electrode fingers in a SAW resonator S1 in the ladder-type SAW device T1 for transmission is made lower than the ratio (LR/PR) of the width LR of electrode fingers to the pitch PR between the electrode fingers in a SAW resonator S2 in the ladder-type SAW device R2 for receiving. As a result, the SAW device D1 has a low loss within a band and has steep attenuation characteristics outside the band, and is miniaturized.