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| Notes for Crystal Unit Applications(石英晶体谐振器使用的注意点) |
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| Notes for Crystal Unit Applications(石英晶体谐振器使用的注意点) |
(1) Compared with the lineups of HC-49/U, small crystal units (HC-49U/S,HC-49USM,UM-1, SMD) are designed to have lower limitable level of drive ,of 100μW and below. Prior to use , therefore, the crystal current should be examined in an actually mounting circuit. (See Fig.5.)
(2) The negative resistance of a circuit must be checked. Confirmation of negative resistance is possible according to Fig.6.A goal of negative resistance is about 5 times the resonance resistance.
(3) The Rd in the circuit diagram is indispensable when used in a C-MOS oscillation circuit. (See fig7.)If this Rd is attached ,the level of drive is kept within the specified value and stable oscillation frequency can be obtained.
(4) Cg and Cd should be used within the range of 10-30pf,if Cg and Cd are used below 10pF or above 30pF,oscillation may be easily affected by circuit performance, level of drive may increase ,or negative resistance may decrease, thus failing in maintaining stable oscillation.
(5) The layout for crystal oscillation circuits should be arranged as short as possible .
(6) The stray capacitance between circuits and ground patterns should be reduced.
(7) Crossing of crystal oscillation circuit patterns over other circuit patterns should be avoided.
(8) If the circuits used ,IC types, and IC manufacturers are different, frequency, level of drive, and negative resistance should be confirmed .
(9) Overtone oscillation circuits need additional consultation.
(1)与HC-49/U相比,小的石英晶体谐振器(如HC-49U/S, HC-49USM, UM-1, 49T) 都是低激励功率(100um或以下). 在使用之前,须在一个实际的安装电路中检验晶体电流(见图5).
(2)须检查电路的负阻抗,负阻抗的认可见图8.
负阻抗应是谐振阻抗的5倍左右.
(3)当使用C-MOS振荡器时(见图7)线路图中的Rd是必要的. 如果Rd达到要求, 激励功率会保持在规定值内,那么谐振频率也就稳定了.
(4)在10-30PF内,可以用Cg和Cd, 如果Cg和Cd<10PF或>30PF, 振荡会被电路现象轻易的影响, 激励功率会升高,或负阻抗会减小, 最终导致振荡的不稳定.
(5)晶体振荡电路的设计应尽量简短.
(6)电路和线路板间的杂散电容应尽量被减少.
(7)尽量避免晶体振荡电路穿过其他电路.
(8)如果电路用IC方式,而且IC制造各不相同,那么频率, 激励功率, 负阻抗须被确认.
(9)泛音振荡电路还需要附加的参考. | |
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