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Wenzel低失真晶体振荡器电路图介绍
This crystal oscillator is designed to operate with fundamental crystals with less than 1 mW dissipated in the crystal. The signal current is filtered by the crystal and develops a voltage across a capacitor with about 500 ohm of reactance. The resulting sinewave has low distortion and phase noise. A JFET buffer is included to drive lower impedance loads. Further buffering with an emitter follower and a voltage step-down transformer or matching network is recommended for driving 50 ohm loads. C3 may be reduced for larger output voltage or to allow lower drive level or it may be increased when lower output levels are desired. The 1k emitter resistor may be replaced with a choke when using overtone crystals. Select the choke to resonate with C2 at a frequency slightly above the fundamental frequency for third overtone crystals. High-Q overtone crystals should be driven at much lower levels than fundamental crystals so select a smaller value for C3 and set the output level as low as possible.Measure the drive level when the crystal's rated current or power is known. The drive level may be determined by temporarly connecting a 100 ohm across C3 and measuring the signal level on the source of the FET. The crystal current is simply V/100.
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部份 |
价值 |
|
Q1 |
2N4401,2N3904,2N2222或其他通用NPN晶体管 |
|
Q2 |
2N4416,2N4858,U310或其他低容量N沟道JFET |
|
R1 |
标称值为10k,选择此值可获得所需的输出电平. |
|
R2 |
470欧姆以节省功率并驱动更轻的负载,100欧姆以驱动更低的阻抗负载. |
|
C1 |
10MHz为100pF,5MHz为220pf,1MHz为1000pF.价值并不重要. |
|
C2 |
10MHz为220pF,5MHz为470pF,1MHz为2200pF.价值并不重要. |
|
C3 |
10MHz为33pF,5MHz为68pF,1MHz为330pF.选择晶体频率为500欧姆电抗的值. |
|
L1 |
选择以使晶体频率居中.可以添加包括变容二极管和微调帽的更复杂的网络. |
|
L2 |
100uH表示10Mhz,470uH表示5MHz,1mH表示1MHz.选择较大的工作频率值. |
该石英晶体振荡器设计用于晶体中耗散小于1mW的基本晶体.信号电流被晶体滤波,并在电容器上产生约500欧姆电抗的电压.产生的正弦波具有低失真和相位噪声.包括JFET缓冲器以驱动较低阻抗负载.建议使用射极跟随器和高压阶跃变压器或匹配网络进一步缓冲,以驱动50欧姆负载.C3可以减小以获得更大的输出电压或允许更低的驱动电平,或者当需要更低的输出电平时可以增加C3.使用非晶体时,1k发射极电阻可以用achoke代替.选择与C2谐振的扼流圈,其频率略高于基频,以获得第三泛音晶体.高Q泛光晶体应以比基本晶体低得多的水平驱动,因此选择较小的C3值并将输出电平设置得尽可能低.当石英晶体的额定电流或功率已知时,测量驱动电平.可以通过临时连接C3上的100欧姆并测量FET的源极上的信号电平来确定驱动电平.晶体电流仅为V/100.
