Acoustic wave filter with cutoff frequency stabilized against temperature drift

摘要

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.