ELECTRIC WAVE FILTERS

• US 3,585,537 A
• Filed: 02/10/1969
• Issued: 06/15/1971
• Est. Priority Date: 02/10/1969
• Status: Expired due to Term

• Current Assignee: Robert C. Rennick, Warren L. Smith
• Original Assignee: Robert C. Rennick, Warren L. Smith
• Inventors: Rennick, Robert C., Smith, Warren L.
• Application Number:
  US04/797,837
• Time in Patent Office: 855 Days
• US Class Current: 333/191
• CPC Class Codes: H03H 9/542 including passive elements H03H9/545 takes precedence
• CPC Class Codes: H03H 9/545 including active elements

Abstract

Multiresonator monolithic crystal structures are coupled to each other at predetermined coupling coefficients K by means of coupling capacitors that shunt the respective structure'"'"''"'"'s resonators to be coupled. The total capacitance coupling the resonators has a value CC C1/K where C1 is the equivalent motional capacitance of the resonators. The capacitor-coupled resonators, when uncoupled, exhibit frequencies f0 1-K, where f0 is the filter'"'"''"'"'s midband frequency.

Claims

1. A filter circuit comprising first monolithic crystal filter means having a plurality of resonator means which define a maximum definitively coupled condition and which are coupled to each other more loosely than said maximum definitively coupled condition, second monolithic crystal filter means having a plurality of resonator means which define a maximum definitively coupled condition and which are coupled to each other more loosely than said maximum definitively coupled condition, and reactance means shunted across each of one of the resonator means in each of said crystal filter means, said resonator means which are shunted being tuned, and said reactance means having a value to maintain a coupling between said resonator means less than the maximum definitively coupled condition, said crystal filter means exhibiting when excited equivalent reactances +X1 and -X1 equal to the motional inductances and motional capacitances of said resonator means at the center frequency fO of said filter circuit, the value of said reactance means being KX1 + OR - 10 percent and including the value of electrostatic reactances of said resonators, K being a desired coupling between said shunted resonators for achieving a given filter characteristic.

2. A filter circuit comprising first monolithic crystal filter means having a plurality of resonator means which define a maximum definitively coupled condition and which are coupled to each other more loosely than said maximum definitively coupled condition, second monolithic crystal filter means having a plurality of resonator means which define a maximum definitively coupled condition and which are coupled to each other more loosely than said maximum definitively coupled condition, and reactance means shunted across each of one of the resonator means in each of said crystal filter means;

said resonator means which are shunted being tuned, and said reactance means having a value to maintain a coupling between said resonator means less than the maximum definitively coupled condition, said reactance means being a capacitor, said crystal filter means exhibiting when excited an equivalent motional inductance L1 and an equivalent motional capacitance C1 at a fundamental frequency fO 1/2 pi L1C1, the value of said capacitor being C1/K + or - 10 percent less the value of electrostatic capacitances in said shunted resonators.

3. A filter circuit comprising first monolithic crystal filter means having a plurality of resonator means which define a maximum definitively coupled condition and which are coupled to each other more loosely than said maximum definitively coupled condition, second monolithic crystal filter means having a plurality of resonator means which define a maximum definitively coupled condition and which are coupled to each other more loosely than said maximum definitively coupled condition, and reactance means shunted across each of one of the resonator means in each of said crystal filter means, said resonator means which are shunted being tuned, and said reactance means having a value to maintain a coupling between said resonator means less than the maximum definitively coupled condition, said crystal filter means exhibiting when excited equivalent reactances +X1 and -X1 equal to the motional inductances and motional capacitances of said resonator means at the center frequency fO of said filter circuit, the value of said reactance means being KX1 + or - 10 percent and including the value of electrostatic reactances of said resonators, K being a desired coupling between said shunted resonators fOr achieving a given filter characteristic, said reactance +X1 being an inductance L1 and said reactance means being an inductance equal to 1/KL1 + or - 10 percent and including the value of electrostatic reactances of said resonators.

4. A filter circuit comprising first monolithic crystal filter means having a plurality of resonator means which define a maximum definitively coupled condition and which are coupled to each other more loosely than said maximum definitively coupled condition, second monolithic crystal filter means having a plurality of resonator means which define a maximum definitively coupled condition and which are coupled to each other more loosely than said maximum definitively coupled condition, and reactance means shunted across each of one of the resonator means in each of said crystal filter means;

said resonator means which are shunted being tuned, and said reactance means having a value to maintain a coupling between said resonator means less than the maximum definitively coupled condition, said circuit exhibiting a given characteristic and passing a given band having a center frequency fO, said reactance means having a value X, said resonator means across which said reactance means are shunted being coupled by a coefficient of coupling K and being tuned when decoupled to a frequency ft fO 1-K + or - 10 percent of the given band.

5. A filter circuit comprising first monolithic crystal filter means having a plurality of resonator means which define a maximum definitively coupled condition and which are coupled to each other more loosely than said maximum definitively coupled condition, second monolithic crystal filter means having a plurality of resonator means which define a maximum definitively coupled condition and which are coupled to each other more loosely than said maximum definitively coupled condition, and reactance means shunted across each of one of the resonator means in each of said crystal filter means, said resonator means which are shunted being tuned, and said reactance means having a value to maintain a coupling between said resonator means less than the maximum definitively coupled condition, said crystal filter means exhibiting when excited equivalent reactances +X1 and -X1 equal to the motional inductances and motional capacitances of said resonator means at the center frequency f0 of said filter circuit, the value of said reactance means being KX1 + or - 10 percent and including the value of electrostatic reactances of said resonators, K being a desired coupling between said shunted resonators for achieving a given filter characteristic, said resonator means shunted by said reactance means being tuned, when decoupled by detuning all other resonators on each of said crystal means, to frequencies ft fO 1-K + or - 10 percent of the band passed by the given characteristic.