Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Patent
1997-12-10
1999-12-21
Dougherty, Thomas M.
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
310366, H03H 956
Patent
active
060053313
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to radioelectronics, more specifically it concerns piezoelectric engineering and can find application in signal frequency discriminators, as well as in developing and manufacture of medium-passband monolithic crystal filters (MCF).
BACKGROUND ART
Known in the present state of the art is a monolithic filter on a crystalline plate from La--Ga silicate (LGS) made on a straight XY-cut. Relative dimensions of the exciting electrodes are in this case as follows: ##EQU1## where Lx is the electrode dimension along electric axis X, m; silicate piezoelectric". In: Electronic engineering. Series "Radioelectronic parts and components", Issue 2 (63), 1986, p.83 (in Russian).
A disadvantage inherent in the known filter resides in a relatively low value of a medium-passband frequency of the filter passband which is not in excess of 20 MHz, this being due to unoptimally selected dimensions of the electrodes with respect x to thickness of the piezoelectric-crystal plate.
One more prior-art monolithic crystal filter is known to comprise at least two acoustically coupled resonators, either of which is established by two overlap exciting electrodes situated on the major faces of a piezoelectric La--Ga silicate wafer of the YXl/.+-..beta..degree. cut, the axis of acoustical coupling therebetween is arranged along the length of the piezoelectric-crystal plate. An angle between the normal to the major wafer face and its mechanical axis Y is selected to be 1.degree. 50'.+-.1.degree., and the length and width of rectangular-shaped exciting electrodes are selected, respectively, from the following relations: ##EQU2## where Lx is the length of exciting electrodes along X axis, m;
A disadvantage of the known filter is a relatively low value of a medium-passband frequency of the filter passband which is not in excess of 20 MHz, this being due to the fact that preselected ratio between the length and width of exciting electrodes, and the thickness of the piezoelectric-crystal plate makes it impossible to realize a technologically small interelectrode gap which is liable to decrease significantly with a frequency raise and with the aforementioned dimensional relations of electrodes; In addition, with a frequency raise discrimination of the filter decreases due to an increase in the level and number of side passbands. Moreover, the aforesaid angle between the normal to the face of the major piezoelectric-crystal plate and its mechanical axis Y equal to 1.degree. 50'.+-.1.degree., fails to provide high temperature stability of the filter medium passband frequency in a wide range of above-zero temperatures.
DISCLOSURE OF THE INVENTION
The present invention has for its principal object to provide a monolithic crystal filter having such a construction arrangement that is instrumental in increasing the medium passband medium, enhancing temperature stability of said medium passband frequency in a wide range of above-zero temperatures, and increasing filter discrimination, which is attained due to a reduced level of side passbands in the filter rejection bands, with the maximum filter transmission band remaining unaffected.
The foregoing object is accomplished due to the fact that in a monolithic crystal filter, comprising at least two acoustically coupled resonators, either of which is established by two overlap exciting electrodes situated on the major faces of a piezoelectric La--Ga silicate wafer of the cut YXl/.+-..beta..degree., the axis of acoustical coupling therebetween is arranged along the length of the piezoelectric-crystal plate, according to the invention, the length and area of the electrodes are selected, respectively, from the following relations: ##EQU3## where Lx is the length of exciting electrodes along X axis, m;
An enhanced temperature stability of the medium passband frequency is attained due to selecting angle .beta. between the normal to the major face of the piezoelectric-crystal plate and its mechanical axis to be within -50'<.beta.<50'.
An increased filter d
REFERENCES:
patent: 4542355 (1985-09-01), Ballato
patent: 5557968 (1996-09-01), Krempl et al.
patent: 5578759 (1996-11-01), Clayton
patent: 5821673 (1998-10-01), Pisarevsky et al.
patent: 5847435 (1998-12-01), Ballato et al.
Translation of priority document RU 95106130.
Translation of claim of SU 1780147 cited in the International Search Report.
Translation of claim of SU 997231 cited in the International Search Report.
Pages 83 and 84 of textbook cited on p. 1 of Specification, plus translation of first paragraph.
Litvinov Valentin Petrovich
Medvedev Andrei Valerievich
Pisarevsky Jury Vladimirovich
Sakharov Sergei Alexandrovich
Dougherty Thomas M.
Rafida Development Incorporated
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