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石英晶体原理,特性,参数,先玉335 转基因应用及使用注意事项介绍
石英晶体等效电路 Vibration of a crystal unit is actually mechanical vibration．However．the crystal unit can be expressed by a two—terminal network if its behavior is electrically converted．The series circuit consisting of L1．C1．and R1 is related to elastic vibration．while the element C0 connected in parallel to the series arm as a capacitance attributable to the dielectric body of a quartz crystal plate．The resistance R1 is a resonance resistance of the crystal unit at the series resonance frequency．(See Fig.1.) 石英晶体谐振器的振动实质上是一种机械振动。实际上，石英晶体谐振器可以被一个具有 电子转换性能的两端网络测出。这个回路包括L1、C1，同时C0作为一个石英晶体的绝缘体的电容被并入回路，与弹性振动有关的阻抗R1是在谐振频率时石英晶体谐振器的谐振阻抗。(见图1) 石英晶体的频率-温度特性
To use a crystal unit as an oscillator．its oscillated frequency is required to be stable against temperature variations．A quartz crystal has crystallographic axes．and crystal cut is defined according to the cutting angle against a crystallographic axis and its associated mode of vibration．-Typical types of crystal cut and frequency—temperature characteristics are shown in Fig.2.
石英晶体作为谐振器在使用时，要求其谐振频率在温度发生变化时保持稳定。温频特性与切割角有关，每个石英晶体具有结晶轴，晶体切割是按其振动模式沿垂直于结晶轴的角度
切割的。典型的晶体切割和温频特性。(见图2)
石英晶体的AT型切片的温频特性
The frequency—temperature characteristics of an AT-Cut crystal unit most generally used at present are expressed by cubic curves．(See Fig.3.)．
A crystal plate is cut at an angle at which a required frequency tolerance is obtained in the given operating temperature range．
AT型石英晶体谐振器的温度特性目前大多用三次曲线表示(见图3)。一个石英芯片在所需要的频率范围己满足的情况下在某一角度被切割，以达到要求的工作温度范围。当然，实际上，即使在成功的操作中，也会有一些由于切割和磨光精确性不够而造成的角度散布，由此，操作的精确度需要提高。在图4中可以看到频率公差和生产难度等级的关系。
石英晶体的负载电容
The load capacitance CL is a factor for determining the "conditions" of a crystal unit when used in the oscillation circuit．In an ordinary oscillation
circuit the crystal unit is used in a range where it functions as an inductive reactance in such usage，the oscillation circuit operates as a apacitive reactance．In other words．when the oscillation circuit is seen from both terminals of the crystal unit．this oscillation circuit can be expressed as a series circuit of a negative resistance -R and a capacitance CL.At that time this capacitance is called the load capacitance．The relationship between load capacitance and oscillation frequency is not linear．When the load capacitance is small．the amount of frequency variation is large．and when the load capacitance iS increased．frequency variation lowers．If the load capacitance is lessened in the oscillation circuit to secure a large allowance for the oscillation frequency．the frequency stability will be greatly influenced even by a small change in the circuit．The load capacitance can be any values．smacbut 10-30PF is better．
负载电容CL是组成振荡电路时的必备条件。在通常的振荡电路中，石英晶体谐振器作为感抗，而振荡电路作为一个容抗被使用。也就是说，当晶体两端均接入谐振回路中，振荡电路的负阻抗-R和电容CL即被测出，这时，这一电容称为负载电容。负载电容和谐振频率之间的关系不是线性的，负载电容小时，频率偏差量大，当负载电容提高时，频率偏差量
减小。当振荡电路中的负载电容减少时，谐振频率发生较大的偏差，甚至当电路中发生一个小变化时，频率的稳定性就受到巨大影响。负载电容可以是任意值，但10-30PF会更佳。
晶体振荡电路中的等效电路
When a crystal unit is actuated as an inductive reactance in an oscillation circuit．the relationship between crystal unit and oscillation circuit is shown in Fig.6. To improve the starting conditions of the oscillation circuit．it is preferable to increase the value of negative resistance -R which parameter of the oscillation circuit．The starting conditions will become worse if a circuit without much allowance in negative resistance (less negative resistance) is combined with a crystal unit having a larger resonance resistance．The oscillation circuit should be designed to a goal such that the value of negative resistance is 5 to 10 times the resonance resistance．It is also necessary that the center value of load capacitance (to determine the absolute value of oscillation frequency) and the variable range (fine adjustment range of oscillation frequency) are maintained at the optimum values in the oscillation circuit．
在振荡电路中，石英晶体谐振器作为感抗被使用。石英晶体谐振器和振荡电路的关系如图5所示，为提高振荡电路中的起振条件，须提高振荡电路中的负阻抗，而电路中没有足够的负阻抗偏差，则较难起振。在振荡电路中负阻抗的值应达到谐振阻抗的5-10倍。在振荡电路中，负载电容的中心值(其决定谐振频率的绝对值)和其变化范围(谐振频率的良好调整范围)应保持在最佳值。
晶体振荡电路
A typical oscillation circuit composed of a crystal unit is introduced below Element constants used are for example．
一个由石英晶体谐振器组成的典型振荡电路如图7所示
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石英晶体的寄生回应
AIl quartz crystals have spurious resonances (unwanted resonance) besides the main resonance frequency．They are represented in the equivalent circuit diagram(Fig.5)by additional resonant circuits in parallel with R1．L1．C1．The ratio of spurious resonance resistance RNW to
resonance resistance Rr of the main wave is generally specified in the attenuation constant dB and designated spurious attenuation aNW:
aNW=-20*lg (Rnw/Rr)
For oscillator crystals 3 to 6 dB are normally sufficient．For filter crystals attenuations greater than 40 dB are often required．This can only be
achieved by special design techniques and involves the use of very small values of the dynamic capacity C1．
The achievable attenuation decreases with higher frequency and with higher orders of overtone．It is found generally that piano-parallel quartz
resonators have better spurious attenuation than piano-convex resonators．In specifying
spurious resonance parameters it is necessary to give an indication of both the acceptable attenuation level desired and their frequencies relative to main resonance frequency．
Resonance in the region of +40 to +150 KHZ for plano parallel resonators biconvex or piano-convex resonators．
In the passive measurement method indicated above，spurious resonance attenuations up to 20 to 30 dB can be measured．With higher attenuations．Co compensation is necessary．
所有石英谐振器均有寄生(在主频率之外的不期望出现的)振荡响应。他们在等效电路图中表现为附加的以R1、L1、C1形成的回应回路。
寄生响应的阻抗RNW与主谐振波的阻抗Rr的比例通常以衰减常数dB来表示，并被定义为寄生衰减
aNW=-20*lg (RNW/Rr)
对于振荡用晶体，3至6dB是完全足够的．对于滤波用晶体，通常的要求是超过40dB．这一规格要求只有通过特殊设计工艺并使用数值非常小的动态电容方能达到．
可达到的衰减随着频率的上升和泛音次数的增加而减小．通常的平面石英芯片谐振器比平凸或双面凸芯片谐振器的寄生衰减要良好．在确定寄生响应参数时，应同时确定一个可接受的寄生衰减水平以及寄生频率与主振频率的相对关系．
在AT切型中，对于平面芯片，"不和谐的响应"只存在于主响应的+40至+150KHZ之间，对于平凸或双面凸的芯片，寄生则在+200至+400KHZ之间．
在以上的测量方法中，寄生响应衰减至20至30dB时是可以测量的，对于再高一些的衰减．C0的补偿是必需的．
Drive Level(DLD)(激励功率依赖性) The amplitude of mechanical vibration of the quartz resonator increases proportionally to the amplitude of the applied current．The power dissipated in the resonance resistance is given by Pc=12qRl．High drive levels lead to the destruction of the resonator or the vaporisation of the evaporated electrodes，The upper limit for drive level is approximately 10 mV As the reactive power oscillating between L1 and C1 is represented 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 exceeted with relatively low level of drive Pc，thus resulting in the crystal frequency moving upwards．
This frequency dependence on drive level is more pronounced with increasing overtone order．Figure 9 shows typical effects but exact prediction of the effect is not possible as it is influenced by all the elements of crystal design and operation．
Mechanical blank parameters．mounting arrangements and so on．Is it can be seen that the drive level must be specified carefully．if there iS to be good correlation between the frequency of the crystal at the end of its production and in the end use equipment．
Today with semiconductor oscillator circuits a drive level of approximately 0.1 MW appears normal．where this parameter is most specified．our
production will use 0.1 Mw．
A well performing crystal should start to oscillate easily and its frequency should be virtrally independent of the variation of drive level from a starting level of about 1 nW．In t
odays semiconductor circuits with very low power consumption the crystal has to work well also at very low drive levels．
泛裸体 In fig.10 we show the effect of crystals with and without the problem of frequency dependence on drive level．
Crystal that have badly adhering electrodes or on which the Surface of the resonator is not fine enough exhibit the curved effect．At low drive level they have higher resistance．
This effect is called the drive level dependence (DLD)．Usually production tests of DLD are performed between 1 and 10 microwatts and then at 1 Mw and again at a low load．The relative change in resistance is then used as the test criterion．Needless to say．making more measurements intermediate level increases production costs considerably．
Using suitable test oscillators permits fast of the DLD limit value．but only in the form of a Go/No-go test．IEC Draft 248 covers measurement of the drive level dependence of the resonance impedance in accordance with (DIN) IEC444-6．
Oscillation build—up problems can very largely be eliminated by optimizing the oscillator circuit by providing a sufficient feedback reserve and a "hard" switch-on pulse．
石英振荡器的机械振动的振幅会随着电流的振幅成正比例地上升．功率与响应阻抗的关系为Pc=l2qR1，高激励功率会导致共振的破坏或蒸镀电极的蒸发，最高允许的功率不应超过lOmV．
由于L1和C1电抗性的功率振荡，存在Qc=QxPc．若Pc=1mV Q=100.000，Qc则相当于IOOW．由于低的Pc功率会导致振荡幅度的超过，最终导致晶体的频率上移．
随着晶体泛音次数的增加，对于激励功率的依赖性更加显著．上图显示了典型的结果，但是精确的预期结果还是要受到包括晶体设计和加工，机械性芯片参数，电极大小，点胶情
况等的影响．
可以看出，激励功率必须被谨慎地确定，以使晶体在生产中和使用中保持良好的关系．
当今，一个半导体振荡回路的激励功率一股为0。1mV故在生产晶体时也一股按0.1mV进行．
上海壹周报 一个质量良好的晶体可以容易地起振，其频率在自lnW逐步增加时均能保持稳定．现在，晶体两端的功率很低的半导体回路也可以在很低的功率的情况下工作良好．
上图显示了一个对激励功率有或无依赖性的晶体的工作曲线的比较．
晶体存在蒸镀电极不良，芯片表面洁净度不足，都会存在如图所示的在低功率时出现高阻抗的情况，这一影响称为激励功率依赖。(DLD)．通常生产中测试DLD是用1～lOmV中华人民共和国检察官法测试后再用lmV测试，发生的阻抗变化可作为测试的标准．很显然，在增加测试内容会相当大的提高晶体生产的成本．
利用适当的测试仪器可以很快地进行DLD极限值的测定，但是只能进行合格/不合格的测试．IEC草案248覆盖了根据(DIV)IEC444-6制定的激励功率的依赖性的测量方法．
提供具有充分的回馈和良好脉冲的最优化的振荡回路，可以极大的消除振荡的内部问题．
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