An improvement method of MCXO

To improve the MCXO performance and simplify its structure, a new MCXO design method was developed in Xidian university. In the MCXO through deleting pulses of clock signal of microcomputer and shifting its phase with quantified time delay approach, the frequency-temperature stability of MCXO can be satisfactory and the DDS chip which is often used in high performance MCXO can be eliminated. Controlled by the software, periodically deleting pulses and shifting the phase of clock signal, the microcomputer can generate a periodic frequency signal with much higher resolution. It is similar to some circuits used in MCXO, the signal is a correction signal. Its period variation is the nominal signal period variation generated by the microcomputer+the deleted clock periods and the shifted phase difference in the period. Its resolution is mush higher than that of the signal based on the microcomputer machine cycle. Because in the MCXO the circuit used to control the VCXO or other devices has the frequency difference multiple function, with this method, the output signal period of the MCXO can be regulated by 0.1 ns to 10 ps resolution. It means the output signal resolution of the MCXO can be 0.01 ppb with respect to the 10 MHz output. The pulse deletion and phase shift have to be synchronized by the signal period generated by the microcomputer. Several different MCXOs have been made with this method and different specifications can be obtained. According to the simplicity, in a wide temperature range from -40/spl deg/C to +80/spl deg/C the frequency-temperature stability of the MCXOs can be from /spl plusmn/3/spl times/10/sup -8/ to /spl plusmn/2/spl times/10/sup -7/ x10.