Cascaded SAW Filter for High Power and Small Size
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Solution Overview
Problem
Existing surface acoustic wave filter apparatuses face challenges in achieving high maximum allowable power without increasing the size, particularly in portable communication devices, where the size of the piezoelectric substrate and chip size are concerns.
Innovation Solution
A surface acoustic wave filter apparatus utilizing a cascade connection of longitudinally coupled resonator SAW filters with a specific configuration of IDTs and reflectors on a piezoelectric substrate, allowing for unbalanced-to-balanced conversion and high maximum allowable power without enlarging the device, achieved by connecting N first longitudinally coupled resonator SAW filters to an unbalanced signal terminal and M second longitudinally coupled resonator SAW filters to balanced signal terminals, where N > M.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If multiple SAW filters are connected in parallel to achieve high maximum allowable power, then the maximum allowable power is improved, but the piezoelectric substrate size increases
Solution Approach 1:
The invention divides the filter system into multiple cascaded stages, each stage consisting of series-connected IDTs and shunt resonators. This segmentation allows the power handling capability to be distributed across multiple stages rather than requiring a single large parallel configuration, thereby achieving high maximum allowable power while maintaining compact substrate size.
Solution Approach 2:
The invention transitions from a two-dimensional parallel arrangement of filters to a multi-stage cascaded structure that utilizes both series and shunt connections. This dimensional reorganization of the circuit topology enables power handling improvement without proportional increase in substrate area, as the power capability is achieved through staged amplification rather than parallel scaling.
2Loss of energy
If multiple SAW filters are connected in parallel to reduce insertion loss, then the insertion loss is reduced, but the piezoelectric substrate size increases
Solution Approach 1:
The filter is segmented into multiple cascaded stages with series IDTs and shunt resonators. This segmentation creates multiple signal paths that can be optimized for low insertion loss while maintaining a compact overall structure, avoiding the need for large parallel configurations.
Solution Approach 2:
The invention merges the functions of multiple filters into a single cascaded structure where series IDTs and shunt resonators work together. This merging achieves the insertion loss reduction benefit of parallel connections while consolidating the implementation into a compact integrated design that reduces substrate area.
3Power
If the number of IDTs is increased to improve power handling, then the power handling capability is improved, but the chip size increases
Solution Approach 1:
The IDTs are segmented into series-connected groups within each stage, with shunt resonators providing power handling enhancement. This segmentation allows power capability to be improved through staged configuration rather than simply increasing the number of IDTs, thereby maintaining compact chip size.
Solution Approach 2:
The invention changes the operational parameters of the IDTs by configuring them in series within cascaded stages, with shunt resonators modifying the impedance characteristics. This parameter change enables improved power handling capability without proportionally increasing chip size, as the power capability is enhanced through parameter optimization rather than simple scaling.
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 enables a high maximum allowable power and noise immunity while maintaining a small size, reducing the number of electrodes in the output area to minimize chip size, and achieving better out-of-band attenuation compared to traditional designs.
Implementation Method 1
A surface acoustic wave filter apparatus includes a piezoelectric substrate, N first longitudinally coupled resonator SAW filters... M second longitudinally coupled resonator SAW filters... IDTs disposed on the piezoelectric substrate in a direction in which a surface acoustic wave propagates
Implementation Method 2
a pair of reflectors disposed on two respective sides, in the direction in which the surface acoustic wave propagates, of an area in which the at least two IDTs are disposed
Data Source
AI summary
In a longitudinally coupled resonator SAW filter apparatus, one end of each N first longitudinally coupled resonator SAW filter, where N is an integer equal to or greater than 2, is connected in parallel to an unbalanced signal terminal, the first N longitudinally coupled resonator SAW filters are connected in a cascade arrangement to M second longitudinally coupled resonator SAW filters, where M is an integer equal to or greater than 1, the M second longitudinally coupled resonator SAW filter are connected to first and second balanced signal terminals, and N and M are selected such that N>M.