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Wenzel低失真晶體振蕩器電路圖介紹
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.
|
部份 |
價(jià)值 |
|
Q1 |
2N4401,2N3904,2N2222或其他通用NPN晶體管 |
|
Q2 |
2N4416,2N4858,U310或其他低容量N溝道JFET |
|
R1 |
標(biāo)稱值為10k,選擇此值可獲得所需的輸出電平. |
|
R2 |
470歐姆以節(jié)省功率并驅(qū)動(dòng)更輕的負(fù)載,100歐姆以驅(qū)動(dòng)更低的阻抗負(fù)載. |
|
C1 |
10MHz為100pF,5MHz為220pf,1MHz為1000pF.價(jià)值并不重要. |
|
C2 |
10MHz為220pF,5MHz為470pF,1MHz為2200pF.價(jià)值并不重要. |
|
C3 |
10MHz為33pF,5MHz為68pF,1MHz為330pF.選擇晶體頻率為500歐姆電抗的值. |
|
L1 |
選擇以使晶體頻率居中.可以添加包括變?nèi)荻O管和微調(diào)帽的更復(fù)雜的網(wǎng)絡(luò). |
|
L2 |
100uH表示10Mhz,470uH表示5MHz,1mH表示1MHz.選擇較大的工作頻率值. |
該石英晶體振蕩器設(shè)計(jì)用于晶體中耗散小于1mW的基本晶體.信號電流被晶體濾波,并在電容器上產(chǎn)生約500歐姆電抗的電壓.產(chǎn)生的正弦波具有低失真和相位噪聲.包括JFET緩沖器以驅(qū)動(dòng)較低阻抗負(fù)載.建議使用射極跟隨器和高壓階躍變壓器或匹配網(wǎng)絡(luò)進(jìn)一步緩沖,以驅(qū)動(dòng)50歐姆負(fù)載.C3可以減小以獲得更大的輸出電壓或允許更低的驅(qū)動(dòng)電平,或者當(dāng)需要更低的輸出電平時(shí)可以增加C3.使用非晶體時(shí),1k發(fā)射極電阻可以用achoke代替.選擇與C2諧振的扼流圈,其頻率略高于基頻,以獲得第三泛音晶體.高Q泛光晶體應(yīng)以比基本晶體低得多的水平驅(qū)動(dòng),因此選擇較小的C3值并將輸出電平設(shè)置得盡可能低.當(dāng)石英晶體的額定電流或功率已知時(shí),測量驅(qū)動(dòng)電平.可以通過臨時(shí)連接C3上的100歐姆并測量FET的源極上的信號電平來確定驅(qū)動(dòng)電平.晶體電流僅為V/100.
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