第二代雙倍資料率記憶體(DDR2 SDRAM)電路佈線性能穩定度之研究

隨著CPU運算頻率的增加，電腦一次所要處理的數據也會相對增加。我們在設計系統的時候，就得需要速度更快的記憶體來處理這些傳輸的資料。原本記憶體只有在時脈上升的時候存取資料，改由在時脈上升及下降的時候各存取一次資料；這就是所謂的雙倍資料率同步動態隨機記憶體：DDR SDRAM (Double Data Rate Synchronous Dynamic Random Access Memory)。當資料處理的速度仍嫌不足時，就將DDR SDRAM再一次做升級。將DDR SDRAM的2位元預取(2 bits Pre-fetch)技術昇級為4位元預取(4 bits Pre-fetch)技術，提高SDRAM資料存取的容量；這就是所謂的第二代雙倍資料率同步動態隨機記憶體：DDR2 SDRAM。本文提出DDR2 SDRAM的電路板(PCB)佈線方法與其準則，同時，我們以一DDR2 SDRAM之時序(Timing)規格的需求為例，設計DDR2 SDRAM模組的PCB佈線。並以示波器測量其位址線、資料線及控制線依照同步時脈動作的時序關係。在同步時脈控制的DDR2 SDRAM模組中，當時脈轉態時，位址線、資料線和控制線的建立時間(Set-up Time)和保持時間(Hold Time)都應符合其規範。本文中所舉例的PCB佈線，其所呈現的Set-up Time和Hold Time皆符合規範。足證明此DDR2 SDRAM模組的PCB佈線方法與準則可做為產業相關設計的參考。

關鍵字

記憶體；同步動態隨機存取記憶體；雙倍資料率記憶體；第二代雙倍資料率記憶體

並列摘要

With the increase of CPU operating frequency, the data that the computer deals with will increase relatively. We need faster memory to deal with the data transmitted when designing product. Original memory is only access data in the rising time, changed into assess data in rising time and falling time; this is DDR SDRAM (Double Data Rate Synchronous Dynamic Random Access Memory). When the speed of access data still can't keep up with the speed of CPU, we improve DDR SDRAM. Upgrade 2 bits Pre-fetch of DDR DRAM to 4 bits Pre-fetch, this is DDR2 SDRAM. In this paper, we propose the method and standard of PCB layout of DDR2 SDRAM. In the mean time, we take demand for Timing standard of a DDR2 SDRAM as an example, to design PCB layout of DDR2 SDRAM module. And measure its address signals, data signals and control signals with oscilloscope, according to the time sequence of pulse movements of synchronous. In DDR2 SDRAM module that pulse movements of synchronous controls, when the pulse was transferred to the status, Set-up Time and Hold Time of address signals, data signals and control signals should all keep its standard. In this article gives an example the PCB wiring, its presents Set-up Time and Hold Time all conform to the standard. Sufficiently proof the PCB wiring method and the criterion of DDR2 SDRAM module may do for the industrial related design reference.