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POLYLITHIC CRYSTAL BANDPASS FILTER HAVING ATTENUATION POLE FREQUENCIES IN THE LOWER STOPBAND

  • US 3,676,806 A
  • Filed: 11/06/1969
  • Issued: 07/11/1972
  • Est. Priority Date: 11/06/1969
  • Status: Expired due to Term
First Claim
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1. A bandpass filter employing piezoelectric crystals as the primary frequency determining elements comprising:

  • a plurality of coupled resonators, having separate piezoelectric crystal bases, connected in tandem, each said coupled resonator comprising a pair of individual resonators sharing the corresponding crystal base, and each said individual resonator having an electrode area on each of the two sides of the base, one electrode being immediately above the other and having physical electrical connections made to each electrode to provide input and output connections, said resonator pair being in spaced relation so that an energy coupling path exists therebetween via the coupled crystal base which path is represented electrically by a mechanical coupling capacitor;

    circuit connections for connecting the output of one of the plurality of coupled resonators to the input of the succeeding coupled resonator thereby forming a junction between adjacent pairs of coupled resonators; and

    resonance means connected across each said junction said resonance means comprising a capacitor and a piezoelectric crystal resonator connected across each junction, said capacitor being selected to provide an equivalent shunt capacitance at said junction that is of the same order of magnitude as the mechanical coupling capacitor of the associated pair of coupled resonators, said resonance means providing an attenuation pole in the lower stopband.

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