DirectX Lighting vs. Real World Lighting （DX光照 對 真實世界光照）
在DX中，我們能創建不同類型的光，使場景看起來更真實。但要記住，DX中的光只是在近似地模擬自然界的光。在自然界中，光由光源（如燈泡）發出，然后延直線傳播，直到消耗完畢或傳入眼睛；光在遇到物體時會發生反射，每次反射都會有能量的消耗；實際上，光可以在物體間反射千百萬次，而且光滑表面會比不光滑的表面反射更多的光。這一切如果全算進來的話，計算量是巨大的，所以，DX只是在近似地模仿。
There are many different (and often confusing) terms associated
with clock-based devices. This application note attempts
to clarify these terms, and hence serves as a comprehensive
reference on clock terminology. This application note can be
divided into two sections. The first section describes and distinguishes
between various clock sources available today.
The second section defines and distinguishes between various
parameters used to describe clocks. This section also provides methods of measuring some of these parameters.
Jitter is extremely important in systems using PLL-based
clock drivers. The effects of jitter range from not having any
effect on system operation to rendering the system completely
non-functional. This application note provides the reader
with a clear understanding of jitter in high-speed systems. It
introduces the reader to various kinds of jitter in high-speed
systems, their causes and their effects, and methods of reducing
jitter. This application note will concentrate on jitter in PLL-based frequency synthesizers.
Cypress Semiconductor makes a variety of PLL-based clock
generators. This application note provides a set of recommendations
to optimize usage of Cypress clock devices in a
system. The application note begins with recommended termination
techniques for clock generators. Subsequently, power
supply filtering and bypassing is discussed. Finally, the application
note provides some recommendations on board
layout.
