Computer system providing low skew clock signals to a synchronous memory unit

Abstract

A computer system is described including a processor for executing instructions, a memory module for storing instructions and data, and a memory controller coupled between the processor and the memory module. The memory controller provides a differential clock signal and memory access signals which are routed to the memory module. The memory module includes multiple memory devices coupled to a clock buffer. The clock buffer produces a new single-ended “regenerated” clock signal from the differential clock signal. The clock buffer includes an input buffer circuit and a phase-locked loop (PLL). The input buffer circuit receives the differential clock signal from the memory controller and produces a single-ended reference clock signal from the differential clock signal. The PLL produces the regenerated clock signal substantially at the same frequency of, and in synchronization with, the single-ended reference clock signal produced by the input buffer circuit. Each of the multiple memory devices is coupled to receive the regenerated clock signal, and the operations of the multiple memory devices are synchronized to the regenerated clock signal. The multiple memory devices within the memory module may be coupled to receive the memory access signals produced by the memory controller, and may store data or retrieve data in response to the memory access signals and the regenerated clock signal. The multiple memory devices may include synchronous dynamic random access memory (SDRAM) devices, and the memory module may be a dual in-line memory module (DIMM).