Design Of High Precision System Clock In Embedded System

With the development of national strategies such as “Made in China 2025”,and the deep integration of traditional industrial and information technologies,the application of embedded system with integrated industrial hardware and software will become more and more widely.This paper focuses on high-precision timing task of light miniaturization embedded system of space vehicle,and does researches on four aspects: the design of high precision clock system,the fast and accurate measurement of crystal frequency,the design of system clock and the on-line measurement of crystal frequency.Firstly,a new high-precision system clock design scheme is proposed.In the space environment caused by crystal oscillator frequency drift factors are two parts.One is the variable frequency drift caused by the temperature effect of the crystal,and the other is the fixed frequency deviation.The design scheme of high precision system clock which eliminates the fixed frequency deviation based on the combination of the short-time on-line short-time measurement of the crystal frequency and the dynamic frequency division of the clock is put forward,which neglects the variable timing deviation caused by the temperature variation.Secondly,the technique of fast and accurate measurement of crystal frequency is studied.A detailed analysis of measurement error sources and methods to reduce measurement error are discussed.In order to reduce the measurement error and the reliability of the system,a frequency adaptive method based on three-mode redundancy and the conditions for short-time measurement are proposed.Thirdly,the design of high precision timing clock is studied.Based on the crystal oscillator timing mechanism,the mechanism of timing deviation is analyzed.Based on the accurate measurement of crystal frequency,a high-precision system clock design is proposed,which does not need the voltage control circuit to change the actual output frequency of the crystal oscillator.The experimental results show that the dynamically divided system clock can eliminate the timing error caused by the crystal fixed frequency difference.Fourthly,the remote frequency measurement technology is studied,and the overall scheme is realized.The interface circuit of communication clock receiving at the time of remote frequency measurement and the criterion of valid edge of clock based on period averaging are designed.The experimental results show that the accurate measurement of crystal frequency can be completed in a short time,and the system clock timing precision generated by dynamic frequency division can meet the requirement of practical application.