Surface-acoustic-wave filters with poles of attenuation created by impedance circuits
AssigneeOki Electric Industry Co., Ltd.
InventorsHisanori Ehara, Kazushige Noguchi, Hajime Shimamura, Yoshio Okada, Tomokazu Komazaki
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Abstract
A surface-acoustic-wave filter couples a two-port surface-acoustic-wave resonator filter circuit coupled in parallel or in series with a two-port impedance circuit. The two-port impedance circuit has an impedance that creates a pole of attenuation, by making the open-circuit impedance of the surface-acoustic-wave filter equal to the short-circuit impedance. High attenuation over a wide range of stopband frequencies is obtained in this way, combined with steep roll-off between the passband and stopband.
Claims28
A surface-acoustic-wave filter with poles, comprising:
- a two-port surface-acoustic-wave resonator filter circuit having a phase shifter, at least one series-arm surface-acoustic-wave resonator coupled in series with said phase shifter, and at least one shunt-arm surface-acoustic-wave resonator;
- and
- a two-port impedance circuit coupled in parallel with said two-port surface-acoustic-wave resonator filter circuit, having an impedance that creates a pole of attenuation by making an open-circuit impedance of said surface-acoustic-wave filter equal to a short-circuit impedance of said surface-acoustic-wave filter.
A surface-acoustic-wave filter with poles, comprising:
- a two-port surface-acoustic-wave resonator filter circuit having two series-arm surface-acoustic-wave resonators coupled in series with a phase shifter, and two shunt-arm surface-acoustic-wave resonators;
- and
- a two-port impedance circuit coupled in series with said two-port surface-acoustic-wave resonator filter circuit, having an impedance that creates a pole of attenuation by making an open-circuit impedance of said surface-acoustic-wave filter equal to a short-circuit impedance of said surface-acoustic-wave filter.
Dependencies are inferred from the claim text.