Series-Connected SAW Filter IDTs for Leakage Power Durability
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Solution Overview
Problem
Conventional surface acoustic wave (SAW) duplexers suffer from poor power durability and non-linearity in the receive filter, leading to leakage power issues that can break the filter or cause sensitivity degradation.
Innovation Solution
A multimode type SAW filter is designed with IDTs connected in series via a floating conductor, where adjacent electrode fingers are connected to either the input/output electrode or ground electrode, reducing electrostatic capacitance and improving power durability while suppressing non-linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional multimode type SAW filter is used in the receive filter, then high out-of-band attenuation and steep cutoff characteristic are achieved, but power durability is poor and non-linearity occurs due to leakage power
Solution Approach 1:
The patent divides a single IDT into multiple IDTs connected in series between the input/output electrode and ground electrode. This segmentation reduces the electrostatic capacitance of each individual IDT, thereby improving power durability and suppressing non-linearity caused by leakage power while maintaining the filter's frequency characteristics.
Solution Approach 2:
The patent changes the electrical parameters by connecting multiple IDTs in series, which reduces the overall electrostatic capacitance compared to a single IDT. This parameter change allows the filter to withstand higher power levels without breaking down or exhibiting non-linear behavior.
2Reliability
If a ladder type SAW filter is used for high power transmission, then power durability is improved, but the receive filter cannot achieve high out-of-band attenuation and steep cutoff characteristic
Solution Approach 1:
The patent applies segmentation to the IDT structure, dividing it into multiple series-connected IDTs. This enables the receive filter to achieve both high power durability (like ladder type) and high out-of-band attenuation with steep cutoff characteristic (like multimode type) by reducing electrostatic capacitance while maintaining the multimode resonance structure.
3Reliability
If leakage power passes through the matching circuit to the receive filter, then the receive filter may break or exhibit non-linearity, but increasing power handling capacity degrades receive sensitivity
Solution Approach 1:
By segmenting the IDT into multiple series-connected units, the patent reduces electrostatic capacitance, allowing the receive filter to handle leakage power without breaking down or exhibiting non-linearity. This maintains receive sensitivity while improving power durability.
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 enhances power durability and reduces non-linearity in SAW filters, preventing filter breakdown and maintaining receive sensitivity without degrading filter characteristics.
Implementation Method 1
A drive voltage is applied to the input IDT, and resultant SAWs are propagated between the reflectors
Implementation Method 2
resultant SAWs are propagated between the reflectors. There are multiple standing waves between the reflectors
Implementation Method 3
A pair of reflectors formed on a piezoelectric substrate, an input IDT and an output IDT are interposed between the pair of reflectors
Data Source
AI summary
A multimode type SAW filter includes a piezoelectric substrate, and IDT groups formed on the piezoelectric substrate, the IDT groups each having multiple IDTs connected in series in which an input/output electrode and a ground electrode are coupled via a floating conductor. Adjacent electrode fingers between adjacent IDTs among the multiple IDTs of the IDT groups include a first electrode finger connected to the floating conductor in one of the IDT groups and a second electrode finger connected to one of the input/output electrode and the ground electrode in another one of the IDT groups.