Elastic Wave Duplexer Circuit for Balanced Signal Isolation
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Solution Overview
Problem
Elastic wave devices with unbalanced-balanced conversion functions exhibit insufficient differential transmission characteristics, including isolation, due to differences in amplitude characteristics between unbalanced and balanced signal terminals, which affect performance in duplexers used in mobile wireless communication.
Innovation Solution
Incorporating first and second inductances with different values between interdigital transducers and ground potential, and optionally capacitances, to adjust and equalize amplitude characteristics between balanced signal terminals, thereby improving transmission and isolation characteristics in a duplexing device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If an unbalanced-balanced conversion elastic wave device is used in a duplexer, then the reception filter can be connected to an IC in the next stage, but the differential transmission characteristics including isolation between transmitted and received signals become insufficient
Solution Approach 1:
The patent applies local quality by making the inductance values asymmetric - specifically setting the inductance connected to the first balanced signal terminal (L1) to be different from the inductance connected to the second balanced signal terminal (L2). This local asymmetry in the electrical characteristics compensates for the phase differences between signals, thereby equalizing the amplitude characteristics and improving differential transmission characteristics without changing the overall unbalanced-balanced conversion structure.
2Adaptability or versatility
If the elastic wave device uses five IDTs with opposite phase configuration, then unbalanced-balanced conversion function is achieved, but amplitude characteristics differ between the two balanced signal terminals
Solution Approach 1:
The patent changes the electrical parameters by introducing inductances L1 and L2 with different values into the circuit. By adjusting these inductance values, the overall electrical characteristics of the device are modified to compensate for the inherent amplitude imbalances caused by the five-IDT opposite-phase configuration, thereby achieving balanced amplitude characteristics while maintaining the unbalanced-balanced conversion function.
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 solution effectively reduces the difference in amplitude characteristics between balanced signal terminals, enhancing transmission and isolation performance in duplexers, particularly in differential mode operations.
Implementation Method 1
first to fifth interdigital transducers (IDTs) 21 to 25 are disposed in that order on the piezoelectric substrate 12
Implementation Method 2
an elastic wave propagation direction along a surface of the piezoelectric substrate 12
Data Source
AI summary
A balanced-unbalanced conversion-type elastic wave device includes an unbalanced signal terminal, first and second balanced signal terminals, and first to fifth interdigital transducers disposed along an elastic wave propagation direction. One end of each of the first, third, and fifth interdigital transducers is connected in common to the unbalanced signal terminal, one end of each of the second interdigital transducer and the fourth interdigital transducer is connected to the first and second balanced signal terminals respectively, a first inductance is connected between the first interdigital transducer and a ground potential, and a second inductance is connected between the fifth interdigital transducer and the ground potential. First and second inductance values of the first and second inductances, respectively, are different.