Acoustic-Wave Receive Filter Topology for Isolation and Harmonic Rejection
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Solution Overview
Problem
Existing acoustic wave filters in multiplexers face challenges in achieving optimal isolation performance and harmonic rejection, particularly in advanced communication systems with carrier aggregation and dual connectivity, due to overlapping reflection coefficients and complex frequency bands.
Innovation Solution
A circuit design incorporating a compensation resonator with a smaller capacitance than other resonators, coupled to the output port, and a series-shunt configuration of acoustic wave resonators to shift angular ranges and prevent overlap of reflection coefficients, enhancing isolation and harmonic rejection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional acoustic wave filter design is used in a multiplexer, then the basic filtering function is achieved, but the isolation performance and harmonic rejection are insufficient due to overlapping reflection coefficients in complex frequency bands
Solution Approach 1:
The filter is segmented into multiple functional sections: a first plurality of series acoustic wave resonators for basic filtering, a second plurality of shunt acoustic wave resonators for harmonic rejection, and a compensation resonator for isolation enhancement. Each section addresses specific performance requirements independently, allowing optimization of isolation performance without requiring complete redesign of the entire filter structure.
Solution Approach 2:
The compensation resonator acts as an intermediary element coupled between the output port and ground. It mediates the interaction between the transmit and receive signals by providing an additional reflection coefficient that prevents overlap with the low noise amplifier's conjugate reflection coefficient, thereby improving isolation performance without directly modifying the main filtering path.
2Reliability
If the number of acoustic wave resonators is increased to improve harmonic rejection, then filtering performance is enhanced, but the device complexity and capacitance overlap increase
Solution Approach 1:
Different resonators are assigned different functional qualities: series resonators (first plurality) are optimized for passband filtering, shunt resonators (second plurality) are optimized for harmonic rejection, and the compensation resonator is optimized for isolation. This local specialization allows each resonator to contribute efficiently to its specific function, achieving high harmonic rejection without requiring excessive numbers of resonators in all positions.
Solution Approach 2:
Instead of adding more series resonators to improve harmonic rejection (conventional approach), the patent inverts the approach by adding shunt resonators coupled to ground at strategic nodes. This inverted topology provides harmonic rejection through parallel resonance paths rather than series resonance, reducing the total number of resonators needed while achieving the same or better performance.
3Measurement precision
If the capacitance of resonators is increased to improve filtering performance, then the frequency selectivity is enhanced, but the angular ranges of reflection coefficients overlap more, reducing isolation
Solution Approach 1:
The compensation resonator provides a counteracting reflection coefficient that balances the phase and magnitude of the overall reflection coefficient. By carefully selecting the capacitance and coupling of the compensation resonator, it creates an anti-weight effect that prevents the angular ranges of reflection coefficients from overlapping, thereby maintaining isolation performance even when other resonators have higher capacitance for improved frequency selectivity.
Solution Approach 2:
The patent optimizes the capacitance values of different resonator groups differently: series resonators have capacitance values optimized for frequency selectivity, while shunt resonators and the compensation resonator have capacitance values optimized to control the phase and magnitude of reflection coefficients. This differential parameter optimization allows frequency selectivity and isolation to be improved simultaneously without the traditional trade-off.
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 provides improved isolation and harmonic rejection in multiplexers, particularly in LTE and 5G NR systems, by minimizing capacitance overlap and optimizing frequency band performance.
Implementation Method 1
An acoustic wave filter can include a plurality of resonators arranged to filter a radio frequency signal. Example acoustic wave filters include surface acoustic wave (SAW) filters and bulk acoustic wave (BAW) filters.
Implementation Method 2
Example acoustic wave filters include surface acoustic wave (SAW) filters and bulk acoustic wave (BAW) filters.
Implementation Method 3
Example acoustic wave filters include surface acoustic wave (SAW) filters and bulk acoustic wave (BAW) filters.
Implementation Method 4
a first angular range that is equal to the angular range of a reflection coefficient of the antenna multiplexer over the transmission frequency band measured looking into the output port of the antenna multiplexer, and a second angular range that does not overlap with the first angular range
Data Source
AI summary
An antenna multiplexer comprising an input port for receiving a transmission signal, a common port, an output port, a transmit filter coupled between the input port and the common port, and a receive filter coupled between the common port and the output port. The receive filter includes a first plurality of acoustic wave resonators in a series path between the common port and the output port and a second plurality of acoustic wave resonators each coupled between the series path and ground. None of the second plurality of acoustic wave resonators are coupled to the output port. The first plurality of acoustic wave resonators including a compensation resonator that is coupled to the output port and has a capacitance that is less than an average of the capacitances of the first plurality of acoustic wave resonators. A module comprising the antenna multiplexer. An electronic device comprising the antenna multiplexer.