【作者】 刘永波；

【导师】 周渭；

【作者基本信息】 西安电子科技大学 ， 测试计量技术及仪器， 2009， 硕士

【摘要】 泛音晶体构成的恒温晶体振荡器(OCXO)具有优良的稳定度和老化指标,但是它的压控频率调节范围很窄,常常难以满足同时对上述指标都有较高要求的情况。尤其是高精度OCXO作为精密的可控频率源时,针对相对宽的频率比对范围OCXO需要能够在频率上被调试、控制,并且保持良好的频率稳定度、老化指标,这是未经过调频扩展的OCXO无法实现的。本文介绍了根据更宽的频率调节范围内采用对OCXO的控制温度进行调整的方法实现扩展频率范围,让恒温晶体振荡器在几个温度点实现分段恒温。本文中采用可程控电位器代替OCXO中控温电桥中的电阻,然后单片机根据锁相环给出的控制信号来控制可程控电位器输出电阻大小从而改变恒温晶体振荡器的恒温温度。通过改变恒温晶体振荡器的恒温温度使OCXO的输出频率改变,从而达到改变恒温晶体振荡器调频范围的目的。本文采用基于CPLD实现的数字锁相环,本锁相环具有锁定速度快、锁相精度高、锁相范围宽的特点。该锁相环可以判断恒温晶体振荡器和标频之间失锁的情况,在失锁情况下还可以给出表示恒温晶体振荡器和标频之间的频率高低关系的控制信号。利用锁相环给出的失锁控制信号,单片机判断并控制可程控电位器输出电阻值,从而改变恒温晶体振荡器的输出频率,最终达到恒温晶体振荡器和标频之间锁定的目的。该方案不仅保证了恒温晶体振荡器原来的频率稳定度,而且把原来的10-7量级的压控频率调节范围扩大到10-6量级甚至更好。更多还原

【Abstract】 High precision oven control crystal oscillator (OXCO) based on overtone crystalscan show very high frequency stability, aging specifications. However, their frequencyregulation range by voltage control is not wide, and it is difficult to obtain all the goodperformances. Especially when high precision OCXO is used as the standard of precisecontrollable measuring instruments, in allusion to widen frequency comparison range,the precision OCXO should not only show nice frequency stability and aging, but alsocan be regulated and controlled in a relative wide frequency range. Using a fundamentalcrystal it is impossible to obtain this result. In allusion to wider frequency regulationrange, we propose a new method through regulating the control temperature of theOCXO to widen the frequency range, the temperature of the OCXO will keep in sometemperature segment.In this paper, a programmable potentiometer is used to substitute the resistor oftemperature-control Bridge. MCU changes the temperature of OCXO by changing theoutput resistor of the potentiometer with the control signal from PLL. The outputfrequency of OCXO will vary with the changing of the OCXO temperature, and thatwill change the output frequency of OCXO. The PLL is designed based on CPLD, thistype PLL has the quality of high precision, high speed locked and wide locked range.This type PLL can determine whether the PLL is locked or not, and it can provide thecontrol signal which can representative the frequency relation between the OCXO andthe standard frequency. MCU can determine and control the output of programmablepotentiometer using the control signal from PLL. By changing the output frequency ofOCXO, finally, OCXO can be locked to frequency standard. This method will retain theprevious frequency stability and phase noise of the OCXO, and the frequency regulationrange will be changed from 10? 7to 10? 6or even better.更多还原