Multiplexer Filter Circuit for Stable Attenuation Pole Frequency
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Solution Overview
Problem
The stability of filter characteristics is compromised due to parasitic inductance variations when filters are mounted on substrates, leading to inconsistent performance across different mounting methods and production tolerances.
Innovation Solution
A filter design incorporating multiple inductors and capacitors, including a resonant circuit with inductors connected in parallel to ground terminals, which stabilizes filter characteristics by minimizing the impact of parasitic inductances, and an acoustic wave resonator to enhance frequency stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single inductor is used in the filter circuit, then the device complexity is reduced, but the filter characteristics become unstable due to parasitic inductance variations from different mounting methods
Solution Approach 1:
The single inductor is segmented into multiple inductors (first inductor L1, second inductor L2, third inductor L3) connected in a specific configuration where L2 and L3 are connected in parallel between node N2 and ground terminals. This segmentation allows the filter to compensate for parasitic inductance variations, as the combined effect of multiple inductors reduces the impact of individual parasitic variations from different mounting methods.
Solution Approach 2:
The invention changes the electrical parameters by introducing multiple inductors with specific inductance relationships (L2 and L3 each have inductance of 0.01 to 0.5 times that of L1). This parameter configuration creates a resonant circuit that forms an attenuation pole, stabilizing the filter characteristics against parasitic inductance variations by adjusting the resonant frequency properties of the circuit.
2Ease of manufacture
If the filter is mounted on a substrate using conventional methods, then the manufacturing process is simple, but parasitic inductance is generated between the ground terminal and substrate, causing characteristic variations
Solution Approach 1:
The second inductor L2 and third inductor L3 act as intermediary elements between the main inductor L1 and the ground terminals. These intermediary inductors create additional current paths that bypass the parasitic inductance generated at the ground terminal mounting interface, thereby reducing the impact of mounting-induced parasitic inductance on overall filter performance.
Solution Approach 2:
The invention applies different inductance values to different parts of the circuit (L1 has a larger inductance value while L2 and L3 have smaller values), creating local quality variations that optimize the circuit's response to parasitic inductance. The parallel connection of L2 and L3 specifically addresses the ground terminal parasitic issue, while L1 maintains the primary filtering function.
3Reliability
If multiple ground terminals are used to reduce parasitic inductance impact, then the filter characteristic stability improves, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The ground connection is segmented into multiple independent ground terminals (first ground terminal and second ground terminal), each connected through separate inductors (L2 and L3). This segmentation allows each ground path to independently handle parasitic inductance, and the parallel configuration ensures that the combined effect stabilizes the resonant frequency and attenuation pole characteristics.
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 proposed filter design significantly reduces the variation in attenuation pole frequencies and improves the stability of filter characteristics, achieving more consistent performance across different mounting conditions.
Implementation Method 1
the capacitive element may be an acoustic wave resonator, and the acoustic wave resonator may form a second local minimum of a second attenuation pole between the first local minimum and the passband
Data Source
AI summary
A filter includes an input terminal, an output terminal, a first ground terminal, a second ground terminal, a first inductor having a first end coupled to a first node in a path between the input terminal and the output terminal and a second end coupled to a second node, a second inductor having a first end coupled to the second node and a second end coupled to the first ground terminal, and a third inductor having a first end coupled to the second node and a second end coupled to the second ground terminal.