Bandstop monolithic crystal filters having allpass response outside stopband |
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Authors: | Lu SKS |
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Institution: | Dept. of Electr. Eng., Malaya Univ., Kuala Lumpar, Malaysia; |
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Abstract: | A dual-resonator monolithic crystal filter (MCF) is basically a narrowband bandpass filter. It is well known that a narrowband bandstop response can be obtained by connecting an inductor in parallel to an MCF element, however, it yields a lowpass response outside the stopband with a cutoff frequency about square root (2) times the stopband frequency. Ideally, outside the stopband, it should have an allpass characteristic. The author shows a simple method of designing a bandstop MCF filter having an allpass response outside the stopband by adding a series-connection inductor. The series inductor together with two capacitors provide the required highpass structure that complements the lowpass response to yield an allpass response.<> |
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