The Research Of OCXO With Wide Frequency Regulation Range

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.