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DKE German Commission for Electrical, Electronic & Information Technologies of DIN and VDE

Overview

This part of IEC 60444 applies to the measurements of drive level dependence (DLD) of quartz crystal units. Two test methods (A and C) and one referential method (B) are described. Method A, based on the method according to IEC 60444-1, can be used in the complete frequency range covered by this part of IEC 60444. Reference Method B, based on the method according to IEC 60444-1, IEC 60444-5 or IEC 60444-8 can be used in the complete frequency range covered by this part of IEC 60444. Method C is an oscillator method which is particularly suitable for measurements of fundamental mode crystal units in larger quantities with fixed conditions. The drive level (expressed as power/voltage across or current through the crystal unit) forces the resonator to produce mechanical oscillations by way of piezoelectric effect. In this process, the acceleration work is converted to kinetic and elastic energy and the power loss to heat. The latter conversion is due to the inner and outer friction of the quartz resonator. The frictional losses depend on the velocity of the vibrating masses and increase when the oscillation is no longer linear or when critical velocities, elongations or strains, excursions or accelerations are attained in the quartz resonator or at its surfaces and mounting points. This causes changes in resistance and frequency, as well as further changes due to the temperature dependence of these parameters. At "high" drive levels (for example, above 1 mW or 1 mA for AT-cut crystal units) changes are observed by all crystal units and these also can result in irreversible amplitude and frequency changes. Any further increase of the drive level may destroy the resonator. Apart from this effect, changes in frequency and resistance are observed at "low" drive levels in some crystal units, for example, below 1 mW or 50 µA for AT-cut crystal units). In this case, if the loop gain is not sufficient, the start-up of the oscillation is difficult. In crystal filters, the transducer attenuation and ripple will change. Furthermore, the coupling between a specified mode of vibration and other modes (for example, of the resonator itself, the mounting and the back-fill gas) also depends on the level of drive. Due to the differing temperature response of these modes, these couplings give rise to changes of frequency and resistance of the specified mode within narrow temperature ranges. These changes increase with increasing drive level. However, this effect will not be considered further in this part of IEC 60444. The first edition of IEC 60444-6 was published in 1995. However, it has not been revised until today. In the meantime the demand for tighter specification and measurement of DLD has increased. In this new edition, the concept of DLD in IEC 60444-6:1995 is maintained. However, the more suitable definition for the user's severe requirements was introduced. Also, the specifications based on the matters arranged in the Stanford meeting in June, 2011 are taken into consideration. This edition includes the following significant technical changes with respect to the previous edition. The DLD measurement with oscillation circuit was moved to Annex B and the multi-level reference measurement method was introduced. The responsible committee is DKE/K 642 "Piezoelektrische Bauteile zur Frequenzstabilisierung" ("Piezoelectric devices for frequency control and selection ") of the DKE (German Commission for Electrical, Electronic and Information Technologies) at DIN and VDE.

Document: references other documents

Responsible national committee

DKE/K 642 - Piezoelektrische Bauteile zur Frequenzstabilisierung und -selektion