Image Number 4 for United States Patent #7619494.
In a ladder-type piezoelectric filter, the attenuation in the stop bands on a low frequency side and a high frequency side are increased while the pass band is widened. The ladder-type piezoelectric filter is made up by alternately connecting parallel arms and series arms. The parallel arms are respectively made up by serially connecting parallel resonators and LC element networks, and the series arms are respectively made up of series resonators. The LC element networks are respectively made up so as to be inductive in resonant frequencies of the serially connected parallel resonators. Further, the LC element networks include capacitors which contribute to formation of a new series resonant point in the stop band on the high frequency side.