Acoustic-Wave Ladder Filter Impedance Tuning for Lower Insertion Loss
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Solution Overview
Problem
Existing SAW ladder filters for diplexers face challenges in meeting specific frequency response specifications due to high insertion loss and sensitivity to resistance values, particularly in achieving optimal performance across various frequency bands.
Innovation Solution
The proposed acoustic-wave ladder filter incorporates a series resonator and a shunt circuit with a functional circuit, including a resistor and an inductor, connected between the series resonator and the grounding terminal, which reduces insertion loss and improves frequency response by optimizing the resistance and inductance values within specific ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a conventional SAW ladder filter is used for a diplexer, then the structure is simple, but the insertion loss is high and the frequency response specification cannot be met
Solution Approach 1:
The filter is divided into multiple resonators (first resonator, second resonator, third resonator) with distinct functions. The first resonator handles the primary filtering function while the second and third resonators form a shunt circuit that specifically addresses insertion loss. This segmentation allows each component to be optimized for its specific role, reducing overall insertion loss while maintaining manageable complexity through modular design.
Solution Approach 2:
The patent introduces a dynamic element - the variable resistor connected in series with the third resonator. This variable resistor allows the filter's electrical characteristics to be dynamically adjusted to optimize performance for different frequency responses. The ability to vary resistance values enables the filter to adapt to different diplexer specifications, improving insertion loss characteristics without permanently increasing structural complexity.
2Reliability
If the resistance value in the shunt circuit is increased to improve frequency response, then the frequency response specification is met, but the sensitivity to resistance values increases
Solution Approach 1:
The patent employs parameter changes by introducing a variable resistor that can be adjusted to different resistance values. This allows the filter to be tuned for optimal frequency response characteristics. The variable resistor enables continuous adjustment of the electrical parameters, allowing the design to meet specific frequency response specifications while finding a balance point that reduces sensitivity to exact resistance values through iterative optimization.
Solution Approach 2:
The measurement and simulation process described in the patent embodies a feedback approach. The filter design is simulated with different resistance values, the frequency response is evaluated against specifications, and adjustments are made accordingly. This iterative feedback process allows the design team to identify resistance values that meet specifications while minimizing sensitivity, effectively using measurement feedback to optimize the balance between reliability and ease of operation.
3Loss of energy
If a shunt circuit with resistor and inductor is added to reduce insertion loss, then the frequency response improves, but the device complexity increases
Solution Approach 1:
The patent merges the shunt circuit components (second resonator, third resonator, variable resistor) into a unified configuration that works synergistically with the first resonator. Rather than adding separate independent circuits, the components are integrated into a cohesive filter structure where the shunt circuit parallel to the first resonator creates a coordinated impedance transformation effect. This merging approach reduces the overall complexity compared to adding multiple separate correction circuits.
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 allows the acoustic-wave ladder filter to meet specific frequency response specifications with reduced insertion loss and improved rejection, enhancing the overall performance of the diplexer by minimizing the sensitivity to resistance values and optimizing the frequency response across the required bands.
Implementation Method 1
The IDT includes two sets of metal strips (electrode fingers), which are formed on the surface of the piezoelectric substrate. The electrode fingers in each set are connected by a bus bar. The SAW impedance element can generate surface acoustic waves in both directions under a condition that a voltage is applied to the two bus bars due to the piezo-effect.
Implementation Method 2
Each of the two reflecting gratings is used to a surface acoustic wave, and includes a periodic system of planar electrodes disposed on an acoustic channel of the IDT.
Data Source
AI summary
An acoustic-wave ladder filter has a first port, a second port and a ground terminal, and includes a series resonator and a shunt circuit. The series resonator is coupled to and disposed between the first and the second ports in series. The shunt circuit is coupled to and disposed between the series resonator and the grounding terminal, and includes a shunt resonator and a functional circuit. The functional circuit is connected in series with the shunt resonator. The functional circuit includes a resistor having a resistance value. The resistance value is greater than 5 Ohms and is smaller than 50 ohms. The functional circuit may further have an inductance.