Acoustic Wave Filter Tuning for Temperature-Stable Cutoff Frequency
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Solution Overview
Problem
Electrical signal processing systems face challenges in achieving a desired frequency response due to temperature and process variations, which affect the resonance and anti-resonance frequencies of acoustic wave filters, leading to interference between TX and RX bands in duplex systems.
Innovation Solution
The implementation of tunable and switchable resonator modules using variable capacitors to modulate the resonate and anti-resonate frequencies of acoustic wave filters, allowing for precise tuning to specific sub-bands and correcting for temperature and manufacturing variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If acoustic wave filters are used in duplex signal transceivers, then signal filtering is achieved, but temperature and process variations cause frequency drift leading to interference between TX and RX bands
Solution Approach 1:
The patent applies dynamics by making the resonator frequencies adjustable rather than fixed. Variable capacitors are coupled to the acoustic wave resonators to dynamically tune the resonate and anti-resonate frequencies, allowing the filter to adapt to temperature and process variations in real-time, thus maintaining reliable frequency response stability despite environmental changes
Solution Approach 2:
The patent implements parameter changes by varying the capacitance values of the variable capacitors to compensate for frequency drift. By changing the electrical parameters (capacitance) in response to detected frequency shifts, the system counteracts the harmful effects of temperature and process variations, preventing interference between TX and RX bands
2Ease of manufacture
If fixed resonator frequencies are used in acoustic wave filters, then manufacturing is simplified, but interference occurs between TX and RX bands due to temperature drift
Solution Approach 1:
The patent applies self-service by enabling the filter to automatically compensate for its own frequency drift. The system uses variable capacitors that can be tuned to counteract temperature and process variations, allowing the filter to self-correct without requiring complex external calibration equipment or manual adjustment, thus maintaining ease of manufacture while eliminating band interference
Solution Approach 2:
The patent implements feedback mechanisms where the actual resonator frequencies are monitored and used to adjust the variable capacitor settings. This closed-loop approach detects frequency drift caused by temperature and process variations and automatically compensates by tuning the resonators, preventing TX-RX band interference while keeping the manufacturing process relatively simple
3Reliability
If variable capacitors are added to tune resonator frequencies, then frequency response stability is improved, but device complexity increases
Solution Approach 1:
The patent applies universality by designing the variable capacitors to serve multiple functions: they not only tune the resonator frequencies for stability but also compensate for both temperature and process variations simultaneously. This multi-functional approach achieves reliable frequency response consistency without requiring separate adjustment mechanisms for different types of drift, thereby limiting the increase in device complexity
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 approach effectively suppresses interference between TX and RX bands, ensuring consistent frequency response and improved signal isolation across various temperature and manufacturing conditions.
Implementation Method 1
An acoustic wave device 80A-BAW, SAW may be represented by an inductor 86A, a capacitor 82B in series and a capacitor 82A in parallel, where the inductor 86A and capacitor 82B represent the elasticity and inertia of the AW 80A-BAW, SAW and the capacitor 82A represents the effective capacitance of the transverse electric fingers in the piezoelectric material
Implementation Method 2
The capacitor 218A may be a variable capacitor whose capacitance may be varied to modulate the AW 214A, 214B for temperature or process variations, or to shift a pass-band or stop-band of the AW 214A, 214B to a different frequency
Data Source
Figure 1A~1B
Figure 1C
Figure 1D
AI summary
An electrical signal processing system includes a fixed (292B) and a tunable (294B) filter. The fixed filter comprises a first acoustic wave resonator whose anti-resonance frequency varies with temperature which results in an undesirable shift of its passband edge (258A, 258B). The tunable filter comprises a second acoustic wave resonator (214A, 214B) and a variable capacitor module (218A) coupled in parallel and has a desirable (302B) and an undesirable (304B) passband. The first acoustic wave resonator is coupled serially to the second acoustic wave resonator for eliminating the undesirable passband. The variable capacitor module variably modifies the anti-resonance frequency of the second resonator to correct for the temperature variation in the anti-resonance frequency of the first acoustic wave resonator. The net frequency response includes only the desirable passband with an acceptable passband loss and minimum stopband attenuation by the desired boundary or frequency cutoff without temperature variations.