Multiplexer Resonator Tuning for Spurious Emission Suppression
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Solution Overview
Problem
Existing multiplexers suffer from attenuation characteristic deterioration outside the second frequency band due to spurious emissions attributed to the interdigital electrode structure of longitudinally coupled resonators.
Innovation Solution
Incorporating an additional circuit with interdigital transducer electrodes on a piezoelectric substrate, where the peak frequency of the additional circuit's response is matched with the lowest impedance frequency of the main filter circuit to prevent spurious emissions, thereby improving attenuation characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an additional circuit with longitudinally coupled resonator is connected to improve attenuation characteristic in predetermined frequency band, then attenuation characteristic in second frequency band is improved, but spurious emissions occur outside the second frequency band causing attenuation characteristic deterioration
Solution Approach 1:
The invention converts the harmful spurious emissions from the IDT electrodes into a beneficial effect by intentionally designing the additional circuit to generate a response at the same frequency as the spurious emission. This response creates an impedance minimum that cancels out the spurious emission, transforming the harmful interference into a useful cancellation mechanism that improves overall attenuation characteristics.
Solution Approach 2:
The invention changes the electrical parameters of the additional circuit, specifically designing the IDT electrode pitch and number of electrodes to control the resonance frequency. By adjusting these parameters, the circuit generates a response at a specific frequency that coincides with the spurious emission frequency, creating an impedance minimum that effectively cancels the harmful emissions while maintaining improved attenuation in the desired frequency band.
2Reliability
If additional circuit is added to improve attenuation, then attenuation characteristic in pass band is improved, but device complexity increases
Solution Approach 1:
The additional circuit serves multiple functions simultaneously: it improves attenuation characteristics in the predetermined frequency band, generates a response to cancel spurious emissions, and creates an impedance minimum at the spurious emission frequency. By designing a single circuit that performs these multiple functions, the invention avoids the need for separate circuits for each function, thereby reducing overall device complexity while achieving the desired performance improvements.
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 solution effectively enhances attenuation characteristics by preventing spurious emissions, ensuring desired attenuation levels of up to 35 dB in the out-of-pass-band frequencies.
Implementation Method 1
a resonator including a plurality of interdigital transducer electrodes on a piezoelectric substrate
Implementation Method 2
a peak frequency for a response that occurs in a bandpass characteristic of the additional circuit and that is attributed to the interdigital transducer electrodes is f1
Data Source
AI summary
A multiplexer includes a first filter connected between a common terminal and an input/output terminal and having a pass band including a first frequency band, a second filter connected between the common terminal and an input/output terminal and having a pass band including a second frequency band higher than the first frequency band, and an additional circuit connected in parallel to a path connecting the common terminal and the input/output terminal. The additional circuit includes a longitudinally coupled resonator including IDT electrodes. If a peak frequency in an IDT response occurring in a bandpass characteristic of the additional circuit is f1, and if a frequency corresponding to a lowest impedance among frequencies higher than the second frequency band in an impedance characteristic viewing the multiplexer from the common terminal is f2, f2×(1−0.0012)≤f1≤f2×(1+0.0012) is satisfied.