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• Drive Level(DLD)
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The amplitude ofmechanical vibration of the quartz resonator increases proportionally to theamplitude of the applied current. The power dissipated in the resonanceresistance is given by Pc=12q R1 . High drive levels lead to the destruction ofthe resonator or the vaporization of the evaporated electrodes, The upper limitfor drive level is approximately 10mW. As the reactive power oscillating betweenL1 and C1 is represent red by Qc =Q X Pc, for Pc=1 Mw and with a Q of 100.000,Qc is equal to 100Watts, The oscillation amplitude can be excreted withrelatively low level of drive Pc, thus resulting in the crystal frequencymoving upwards.

This frequencydependence on drive level is more pronounced with increasing overtone order.The crystal unit is an electronic device that is capable of composing afrequency generator circuit with an extremely high stability .It has achievedhigh degree of compactness and high performance . Fig 5. Shows typical effectsbut exact prediction of the effect is not possible as it is influenced by allthe elements of crystal design and operation. Mechanical blank parameters,electrode size, mounting arrangements and so on. Is it can be seen that thedrive level must be specified carefully, if there is to be good correlationbetween the frequency of the crystal at the end of its production and in theend use equipment.

Today withsemiconductor oscillator circuits a drive level of approximately 0.1Mw appearsnormal, Where this Parameter is most specified, our production will use 0.1mW.A well performing crystal should start to oscillate easily and its frequencyshould be virtually independent of the variation of drive level from a startinglevel of About 1 n W. In toadies semiconductor circuits with very low powerconsumption the crystal has to work well also at vet low drive levels.In Fig. 6we show the effect of crystals with and without the problem of frequencydependence on drive level.Crystal that have badly adhering electrodes or onwhich the surface of the resonator is not fine enough exhibit the curvedeffect. At low drive levels they have higher resistance. This effect is calledthe drive level dependence (DLD). Usually production tests of DLD are performedbetween 1 and 10 microwatts and then at 1 Mw and again at a low load. Therelative change in resistance is then used as the test criterion. Needless tosay, making more easurements at intermediate level increases crystal productioncosts considerably.