Langasite crystal resonators
Special features of the langasite crystal resonators
Lanthanum gallium silicate (langasite, LGS) - the synthetic single crystal, reared by Czochralski's method. The structure of crystal lattice of langasite is similar to crystal lattice of quartz, this determined its application in the production of piezoelectric resonators. The presence of cut with the zero temperature frequency coefficients for the dominant modes of oscillations, in combination with the high values of electromechanical coupling factors for these forms of fluctuations makes it possible effectively to use it langasite for the wide-band resonators with the high capability for reconstruction of frequency.
The acoustic quality of langasite, measured on the sound attenuation in a single crystal, is higher than in quartz. At the same time, the quality of langasite resonators is lower than in analogous quartz. This effect is caused not energy losses in the crystal of langasitae, but with the high values of electromechanical force factors. Simultaneously, from such important parameters as lasting stability and suppression level flicker - noise langasite resonators is not worse than quartz analogs.
The temperature-frequency characteristic of resonators from langasite is quadratic parabola with the slope of 7x10-8 (°C) - 2, practically for all forms of 
fluctuations. The position of the extremum of temperature-frequency characteristic can be changed in the limits from 0 to 100°C, depending on the angle of the cut of crystalline element. Thus, langasite resonators can effectively be used both in the voltage controlled oscillators and in the temperature-compensated and oven-controlled oscillators.
The capacitive relation of langasite for the resonators is thickness shear fluctuations it composes 60… 120, that into 2… 3 times less than in the quartz resonators of AT- cut. Therefore the application of langasite resonators instead of the traditional quartz in the wide-band filters makes it possible to forego the trimming elements and to considerably decrease the overall dimensions of electronic components. The use of langasite resonators in the voltage controlled crystal oscillators makes it possible to substantially increase the limits of reconstruction of frequency. Thus, the value of reconstruction of frequency, obtained with the use in the generator of langasite resonators with the fluctuations of shift on the thickness for the frequency of 60 MHz without the trimming elements, composed 5000 ppm.
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Frequency range, MHz | Accuracy of adjustment, ppm | Dynamic resistance, Ohm | Crystal enclosure | |
|---|---|---|---|---|---|
10-100 |
±5...±50 |
5...100 |
EK, EJ |
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