Acoustic Wave Multiplexer Using SAW Shunt for Harmonic Suppression
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Solution Overview
Problem
Existing acoustic wave filters, particularly those using bulk acoustic wave (BAW) resonators, face challenges in achieving low second harmonic distortion, which is becoming increasingly demanding in certain applications such as 5G New Radio (NR) systems.
Innovation Solution
The proposed solution involves a multiplexer design that includes a receive filter with a shunt surface acoustic wave (SAW) resonator and a plurality of bulk acoustic wave (BAW) resonators. The shunt SAW resonator has a resonant frequency within the transmit passband, reducing second harmonic distortion at the common node.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If bulk acoustic wave resonators are used in the filter, then the filter can achieve good frequency selectivity and high power handling, but the second harmonic distortion increases
Solution Approach 1:
A shunt surface acoustic wave resonator is introduced as an intermediary element between the bulk acoustic wave resonators and the common node. This SAW resonator acts as a mediator that suppresses the second harmonic distortion generated by the BAW resonators while preserving their frequency selectivity and power handling capabilities. The shunt configuration allows it to effectively shunt the second harmonic signals away from the output.
2Object-generated harmful factors
If multiple types of acoustic wave resonators are combined, then the second harmonic distortion is reduced, but the device complexity increases
Solution Approach 1:
Instead of replacing all resonators with a different type, the invention applies local quality by using surface acoustic wave resonators specifically at critical locations (shunt positions near the common node) where second harmonic suppression is most needed, while maintaining bulk acoustic wave resonators in series positions where their high power handling and frequency selectivity are most beneficial.
3Object-generated harmful factors
If the shunt resonator resonant frequency is set within the transmit passband, then the second harmonic distortion is suppressed, but the insertion loss in the receive passband may increase
Solution Approach 1:
The invention inverts the conventional approach by placing the shunt resonator's resonant frequency within the transmit passband rather than the receive passband. This unconventional frequency placement allows the shunt resonator to effectively suppress second harmonic distortion in the transmit path while having minimal impact on receive passband insertion loss, as the resonator appears as a high impedance at receive frequencies.
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 design effectively reduces second harmonic distortion in the transmit filter, improving the linearity and meeting the stringent specifications of 5G NR applications while maintaining low insertion loss in the receive passband.
Implementation Method 1
A surface acoustic wave resonator can include an interdigital transductor electrode on a piezoelectric substrate. The surface acoustic wave resonator can generate a surface acoustic wave on a surface of the piezoelectric layer on which the interdigital transductor electrode is disposed.
Implementation Method 2
A surface acoustic wave resonator can include an interdigital transductor electrode on a piezoelectric substrate
Implementation Method 3
In BAW resonators, acoustic waves propagate in a bulk of a piezoelectric layer
Data Source
AI summary
Aspects of this disclosure relate to multiplexers with acoustic wave resonators. The multiplexer includes a first filter and a second filter. The first filter includes a plurality of bulk acoustic wave resonators and a shunt surface acoustic wave resonator. The shunt acoustic wave resonator can have a resonant frequency in a passband of the second filter. The passband of the second filter is below a passband of the first filter. In certain applications, the first filter is a receive filter and the second filter is a transmit filter.