The design of high precision time keeping clock system

Abstract

This paper presents the design of a high-precision time keeping clock system. The system mainly consists of high-precision crystal oscillator, the accumulator (ACC), and Time Digital Convert (TDC) module. The high-precision crystal oscillator generates a pulse with the fixed cycle, and the pulse is taken as the input clock of ACC to make ACC self added according to the pre-set step. Then the overflowed signal of ACC acts as the output signal of the system’s time keeping clock. When working, the system accurately measures the period of the high precision oscillator by use of the TDC module, and then the ACC stepping values are adjusted according to the measured results. It makes the overflowed signal of ACC remain the period as a high-accuracy clock signal. The system effectively eliminates the time keeping error which comes from the error and aging of the crystal. Experiments show that the system greatly reduces the cumulative time error, and the average cumulative time keeping error is 6.5ns in one week with the time keeping mean square error of 43ns.