US3656180A - Crystal filter - Google Patents

Crystal filter Download PDF

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Publication number
US3656180A
US3656180A US63204A US3656180DA US3656180A US 3656180 A US3656180 A US 3656180A US 63204 A US63204 A US 63204A US 3656180D A US3656180D A US 3656180DA US 3656180 A US3656180 A US 3656180A
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Prior art keywords
resonator
resonators
circuited
ungrounded
short
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Expired - Lifetime
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US63204A
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English (en)
Inventor
Arthur Rechtman Braun
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AT&T Corp
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Bell Telephone Laboratories Inc
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
    • H03H9/46—Filters
    • H03H9/54—Filters comprising resonators of piezoelectric or electrostrictive material
    • H03H9/56—Monolithic crystal filters
    • H03H9/566—Electric coupling means therefor

Definitions

  • FIG. 2 INPUT OUTPUT DETECTOR //v l/EN TOR A. R. BRA UN ATTORNEY PATENTEDAPR 1 1 I972 SHEET OZUF 10 FIG. 2
  • FIG 4A FREQUENCY IN MH Z PATENTEDAPR 11 :912 3,656,180
  • This invention relates to energy translating devices and, more particularly, to monolithic crystal filters.
  • the term monolithic crystal filter as used herein is meant to define the basic filter structure disclosed by W. D. Beaver and R. A. Sykes in their copending application Ser. No. 558,338, filed June 17, 1966, now US. Pat. No. 3,564,463 issued Feb. 16, 1971.
  • the Beaver-Sykes apparatus is an energy translating device for translating input oscillatory electrical energy having first characteristics into output oscillatory electrical energy having second characteristics.
  • One specific use to which such a structure may be put is that of a filter.
  • such a filter involves the use of two or more resonators which share a common piezoelectric body or wafer.
  • the Beaver-Sykes structure is distinguished from other outwardly similar structures by the combination of two features, namely, mass loading and acoustic coupling.
  • mass loading refers to a particular electrode mass which is determined by the nature of the piezoelectric body and its thickness and by the size and density of the electrodes which make up each of the resonators. Mass loading which conforms to the principles taught by Beaver and Sykes is evidenced by a number of specific conditions. For example, acoustic energy supplied in or near to one of the resonators is essentially confined or trapped within the boundaries of the resonator so that very little escapes to the surrounding piezoelectric body.
  • the relatively limited amount of acoustic energy that does escape from the energy trapping zone of the resonator decreased exponentially in magnitude as the distance from the resonator increases.
  • the contour and dimensions of the outer perimeter of the piezoelectric body have no effect on the nature of the energy transmission accomplished.
  • Acoustic coupling refers to the existence of an energy channel in the piezoelectric body which effects the transmission of acoustic energy between input and output electrodes. Such coupling is evidenced or manifested by a number of conditions which include, for example, the placing of all resonators within the acoustic field of adjacent resonators. Further, the only physical connecting path between the input and output resonators is in the piezoelectric body, and substantially all of the energy transferred from one resonator to another is acoustic energy.
  • the image impedance of the structure or circuit as a whole conforms to a specifically defined pattern; and also, the structure or circuit as a whole has an equivalent circuit in the form of a lattice network with resonant and antiresonant frequencies characterized by a specifically defined relation.
  • the transfer characteristics of a filter should be marked by steep skirts of attenuation and the passband should be bracketed by distinct attenuating peaks.
  • peaks of attenuation have been achieved in monolithic crystal filters only by the use of electrical coupling which entails the use of an external capacitor to couple two or more resonators or by charge cancellation where portions of split electrodes are coupled directly.
  • Charge cancellation has proved to be ef fective only in two-pole filters, however, and such filters have a very limited range of practical use.
  • the general object of this invention is to improve the transfer characteristics of monolithic crystal filters, including multiple pole filters, without employing discrete coupling elements between resonators.
  • a monolithic crystal filter which employs an ungrounded intermediate resonator with the electrodes thereof short circuited, which resonator is positioned between the input and output resonators of the filter.
  • the input wave is applied not only to the input resonator, but also to the 0 intermediate resonator.
  • the input resonator vibrates conventionally in the thickness shear mode to create a first or primary acoustic wave.
  • a secondary wave similar in magnitude but displaced in phase, is generated by the intermediate or quasi resonator..
  • the principles of the invention turn to account the relative phase of the two mechanical waves as they travel down the piezoelectric plate or wafer, and at those frequencies at which the waves are equal in magnitude but 0pposite in phase, a peak of attenuation occurs.
  • the primary and secondary waves cancel each other at at least two frequencies which bracket the filter passband and as a result, the selectivity characteristics of the filter are substantially enhanced.
  • FIG. 1 is a schematic circuit diagram of a filter in accordance with the invention.
  • FIG. 2 is a schematic circuit diagram of a second embodiment of a filter in accordance with the invention.
  • FIG. 2A is a plot illustrating the characteristics of the filter of FIG. 2;
  • FIG. 3 is a schematic circuit diagram of a third embodiment of a filter in accordance with the invention.
  • FIG. 3A is a plot illustrating the characteristics of the filter of FIG. 3;
  • FIG. 4 is a schematic circuit diagram of a fourth embodiment of a filter in accordance with the invention.
  • FIG. 4A is a plot illustrating the characteristics of the filter of FIG. 4.
  • FIG. 5 is a schematic circuit diagram of a fifth embodiment of a filter in accordance with the invention.
  • FIG. 5A is a plot illustrating the characteristics of the filter of FIG. 5;
  • FIG. 6 is a schematic circuit diagram of a sixth embodiment of a filter in accordance with the invention.
  • FIG. 6A is a plot illustrating the characteristics of the filter of FIG. 6;
  • FIG. 7 is a schematic circuit diagram of a seventh embodiment of a filter in accordance with the invention.
  • FIG. 7A is a plot illustrating the characteristics of the filter of FIG. 7;
  • FIG. 8 is a schematic circuit diagram of an eighth embodiment of a filter in accordance with the invention.
  • FIG. 8A is a plot illustrating the characteristics of the filter of FIG. 8;
  • FIG. 9 is a schematic circuit diagram of a ninth embodiment of a filter in accordance with the invention.
  • FIG. 9A is a plot illustrating the characteristics of the filter of FIG. 9;
  • FIG. 10 is a schematic circuit diagram of a circuit for measuring certain of the characteristics of a filter in accordance with the invention.
  • FIG. 10A is a vector representation of certain of the voltages designated in FIG. 10.
  • FIG. 11 and FIG. 11A are amplitude frequency plots of the combination of the primary and secondary waves generated within a filter in accordance with the invention.
  • FIG. 1 discloses an eight-pole commercial monolithic crystal filter modified in accordance with the principles of the invention.
  • the electrodes of the resonators 1-8 are shown as spaced from the piezoelectric body or wafer P although in fact the electrodes are in contact therewith.
  • each of the resonators from the input resonator on the left to the output resonator on the right is numbered consecutively 1 through 8.
  • Resonators 2,4,5,6 and 7 are convention intermediate grounded resonators, intermediate in the sense that they are placed between the input resonator l and the output resonator 8. These intermediate resonators help to shape the passband characteristics as explained in detail in the copending application of R. L. Reynolds and R.
  • FIG. 1 shows the quasi resonator 3 employing a single set of electrodes, the principles of the invention also include coupling together various numbers of intermediate ungrounded resonators or electrode pairs to serve in combination as a single quasi resonator. Such an arrangement is illustrated by the circuit of FIG. 2.
  • the peaks of attenuation occurring in a filter characteristics plot are directly dependent on the particular relative position of the resonator or combination of resonators employed to generate the secondary wave.
  • curves labeled A indicate characteristics of a conventionally connected filter
  • curve B illustrates the characteristics of a filter connected in accordance with the invention as shown in the correspondingly numbered figure.
  • skirt attenuation is increased somewhat but no strong peaks of attenuation are introduced when the single resonator 2 of FIG. 2 is employed as the quasi resonator.
  • resonator 3 is connected as shown in FIG. 4 some additional increase in skirt attenuation results, as shown in FIG. 4A.
  • resonator 4 is used to generate the secondary wave, as shown in FIG. 5, relatively strong peaks of attenuation are created with a further increase in skirt attenuation as shown in FIG. 5A.
  • the effect of employing a combination of electrodes, for example electrodes 2 and 3, to generate the secondary wave, as shown in FIG. 6 produces the results illustrated by the curves of FIG. 6A; and the results of employing the combination of resonators 3, 4, and 5 as shown in FIG. 7 are illustrated by the curves of FIG. 7A.
  • curve A is the plot of the filter with all intermediate resonators conventionally grounded; curve C results from connecting the filter as shown in FIG. 9 but with the generation of a secondary wave only; and curve B is the plot of the filter connected as shown in FIG. 9 in which both the main and secondary waves are generated.
  • FIG. 11 and FIG. 11A are graphical representations of the resultant amplitude versus frequency. These peaks and the frequencies at which they occur are illustrated by curve B in FIG. 9A. It will be noted that in FIGS. 11A and 11B the minimum occurs at these frequencies, thus corroborating the existence of the transmission zeros and the existence of a secondary wave.
  • a monolithic crystal filter comprising, in combination, a plurality of resonators each including a respective portion of a common piezoelectric body sandwiched between a respective pair of electrodes, said resonators including an input resonator, an output resonator and intermediate resonator means positioned therebetween, at least one opposing pair of said electrodes of said intermediate resonator means being short circuited and ungrounded, means for applying a common input signal simultaneously to said input resonator and to said last named electrodes, whereupon a primary acoustic wave and a secondary acoustic wave substantially equal in magnitude but different in phase are generated in said body, thereby enhancing the degree of selectivity of said filter.
  • said intermediate resonator means includes at least one grounded resonator on either side of said short-circuited and ungrounded electrodes.
  • said intermediate resonator means includes a plurality of ungrounded, short-circuited resonators to which said input signal is applied and a plurality of grounded resonators.
  • Apparatus in accordance with claim 4 further including at least one short-circuited ungrounded resonator having no means for the direct application of an external signal thereto.
  • Apparatus in accordance with claim 4 further including at least one short-circuited ungrounded resonator having no means for the direct application of an external signal thereto positioned on either side of said ungrounded short-circuited resonators to which said input signal is applied.
  • Apparatus in accordance with claim 6 including conducting means interconnecting said ungrounded short-circuited resonators to which no input signal is applied.
  • a monolithic crystal filter comprising, in combination, a plurality of resonators each including a respective portion of a common piezoelectric body sandwiched between a respective pair of said electrodes, said resonators including an input resonator, an output resonator and intermediate resonator means positioned therebetween, said intermediate resonator means including at least one ungrounded short-circuited resonator, means for applying a common input signal simultaneously to said input resonator and to said ungrounded short-circuited resonator, and means for deriving an output signal from said output resonator.
  • said intermediate resonator means further includes at least one grounded resonator.
  • said intermediate resonator means further includes at least one grounded resonator and at least one ungrounded short-circuited resonator having no means for the direct application of an input signal thereto.
  • Apparatus in accordance with claim 8 wherein the energy transferred to said output resonator during operation is substantially entirely acoustic.
  • said intermediate resonator means includes a first plurality of ungrounded short-circuited interconnected resonators thereby to enable simultaneous application of said input signal to said input resonator and to said plurality of resonators, at least two additional ungrounded short-circuited interconnected resonators bracketing said plurality of resonators, and a second plurality of grounded resonators, whereby the phase cancellation that occurs as the result of the interaction between the primary acoustic wave generated by said input resonator and the second acoustic wave generated by said first plurality of resonators creates peaks of attenuation bracketing the bandpass of said filter.

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  • Chemical & Material Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • Piezo-Electric Or Mechanical Vibrators, Or Delay Or Filter Circuits (AREA)
US63204A 1970-08-12 1970-08-12 Crystal filter Expired - Lifetime US3656180A (en)

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US6320470A 1970-08-12 1970-08-12

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US (1) US3656180A (xx)
JP (1) JPS5116093B1 (xx)
BE (1) BE771051A (xx)
CA (1) CA925967A (xx)
DE (1) DE2139218C3 (xx)
ES (1) ES394607A1 (xx)
FR (1) FR2104192A5 (xx)
GB (1) GB1363918A (xx)
NL (1) NL162523C (xx)
SE (1) SE361800B (xx)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3739304A (en) * 1971-09-27 1973-06-12 Bell Telephone Labor Inc Resonator interconnections in monolithic crystal filters
US3866155A (en) * 1972-09-20 1975-02-11 Oki Electric Ind Co Ltd Attenuation pole type monolithic crystal filter
US3944951A (en) * 1974-11-21 1976-03-16 Bell Telephone Laboratories, Incorporated Monolithic crystal filter
US3947784A (en) * 1974-09-19 1976-03-30 Motorola, Inc. Dual-coupled monolithic crystal element for modifying response of filter
US4484158A (en) * 1982-07-07 1984-11-20 General Electric Company Monolithic crystal filter and method of manufacturing same
US4604543A (en) * 1984-11-29 1986-08-05 Hitachi, Ltd. Multi-element ultrasonic transducer
US6448695B2 (en) * 2000-06-20 2002-09-10 Koninklijke Philips Electronics N.V. Bulk acoustic wave device

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2198684A (en) * 1938-09-20 1940-04-30 Bell Telephone Labor Inc Wave filter
US2373431A (en) * 1943-03-30 1945-04-10 Bell Telephone Labor Inc Electric wave filter
US3185943A (en) * 1956-04-23 1965-05-25 Toyotsushinki Kabushiki Kaisha One-piece mechanical filter having portions forming plural resonators and coupling means
US3222622A (en) * 1962-08-14 1965-12-07 Clevite Corp Wave filter comprising piezoelectric wafer electroded to define a plurality of resonant regions independently operable without significant electro-mechanical interaction
US3334307A (en) * 1966-11-14 1967-08-01 Zenith Radio Corp Multi-electrode acoustic amplifier with unitary transducing and translating medium
US3396329A (en) * 1963-12-12 1968-08-06 Commissariat Energie Atomique Magnetic resonance magnetometers for measuring weak magnetic fields from aboard a moving vehicle, as a plane

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2198684A (en) * 1938-09-20 1940-04-30 Bell Telephone Labor Inc Wave filter
US2373431A (en) * 1943-03-30 1945-04-10 Bell Telephone Labor Inc Electric wave filter
US3185943A (en) * 1956-04-23 1965-05-25 Toyotsushinki Kabushiki Kaisha One-piece mechanical filter having portions forming plural resonators and coupling means
US3222622A (en) * 1962-08-14 1965-12-07 Clevite Corp Wave filter comprising piezoelectric wafer electroded to define a plurality of resonant regions independently operable without significant electro-mechanical interaction
US3396329A (en) * 1963-12-12 1968-08-06 Commissariat Energie Atomique Magnetic resonance magnetometers for measuring weak magnetic fields from aboard a moving vehicle, as a plane
US3334307A (en) * 1966-11-14 1967-08-01 Zenith Radio Corp Multi-electrode acoustic amplifier with unitary transducing and translating medium

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3739304A (en) * 1971-09-27 1973-06-12 Bell Telephone Labor Inc Resonator interconnections in monolithic crystal filters
US3866155A (en) * 1972-09-20 1975-02-11 Oki Electric Ind Co Ltd Attenuation pole type monolithic crystal filter
US3947784A (en) * 1974-09-19 1976-03-30 Motorola, Inc. Dual-coupled monolithic crystal element for modifying response of filter
US3944951A (en) * 1974-11-21 1976-03-16 Bell Telephone Laboratories, Incorporated Monolithic crystal filter
US4484158A (en) * 1982-07-07 1984-11-20 General Electric Company Monolithic crystal filter and method of manufacturing same
US4604543A (en) * 1984-11-29 1986-08-05 Hitachi, Ltd. Multi-element ultrasonic transducer
US6448695B2 (en) * 2000-06-20 2002-09-10 Koninklijke Philips Electronics N.V. Bulk acoustic wave device

Also Published As

Publication number Publication date
SE361800B (xx) 1973-11-12
NL7111061A (xx) 1972-02-15
NL162523B (nl) 1979-12-17
FR2104192A5 (xx) 1972-04-14
ES394607A1 (es) 1975-04-01
JPS5116093B1 (xx) 1976-05-21
BE771051A (fr) 1971-12-16
CA925967A (en) 1973-05-08
GB1363918A (en) 1974-08-21
DE2139218A1 (de) 1972-02-17
AU3202771A (en) 1973-02-08
NL162523C (nl) 1980-05-16
DE2139218B2 (xx) 1974-05-09
DE2139218C3 (de) 1974-12-19

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