An adjustable design with component tolerance for the Real Time Clock of high-end server systems

Abstract

The method we described in this paper is an adjustable design method for more environmental temperature tolerance both with considered components tolerance and temperature characteristics of a Real Time Clock (RTC) circuit on a high end server system. The current RTC source is used on server system categories with a crystal unit, SPXO and TCXO, of which crystal unit is usually used to provide a cost benefit. We propose to reduce those factors which may affect the RTC circuit, such as the PCB (Printed Circuit Board) stack-up, the parasitic capacitance of the PCB trace layout, the equivalent capacitance of the chipset and crystal unit, and also the temperature characteristics of a BT section crystal unit. We enumerate major factors and come up with an external load capacitor value to provide the load capacitance which the oscillator circuit actually needs, to make the RTC clock rate more accurate. And we consider the tolerance of the RTC oscillator circuit and the temperature characteristics of a crystal unit in order to obtain larger design tolerance.