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INTRODUCTION
( G2 k/ W+ g2 i' Q/ `5 lThe most important factor in the design of many systems today is speed. 66-MHz thru 200-MHz6 m- r( ~" O4 Q
processors are common; 233 and 266-MHz processors are becoming readily available. The demand+ k* s- z4 u5 X/ p2 z/ o
for high speed results from: a) the requirement that systems peRForm complex tasks in a time frame
( {- P2 z" l4 aconsidered comfortable by humans; and b) the ability of component manufacturers to produce0 {$ c/ B7 j7 P) b* A" @
high-speed devices. An example of a) is the large amount of information that must be processed
/ V5 R+ i: r* m& S$ d9 B' m( Xto perform even the most rudimentary computer animation. Currently, Programmable Array Logic% }2 k7 W, F2 M# p8 |
(PAL®) devices are available with propagation delays of 4.5 ns, and complex PLDs such as MACH7 A( r) u- V2 X& N$ U. f
®have propagation delays of 5 ns. While this might seem fast, it is not the propagation delay that
& l8 t: C4 m2 p) S {creates the potential for problems, but rather the fast edge rates needed to obtain the fast3 H, q) }2 v* U# F4 [2 b
propagation delays. In the future, much faster devices will become available, with correspondingly
+ }* H+ w7 H& K3 M8 C! K2 Jfaster edge rates.$ z* }2 W2 c8 l2 L. W* Y
Designing high-speed systems requires not only fast components, but also intelligent and careful( R4 a: M& p" b
design. The analog aspect of the devices is as important as the digital. In high-speed systems, noise- k) m: \8 V. A( h6 T+ I
generation is a prime concern. The high frequencies can radiate and cause interference. The! B# j) M! d+ G- i" N
corresponding fast edge rates can result in ringing, reflections, and crosstalk. If unchecked, this* |. _! \& ~6 \; c! D
noise can seriously degrade system performance.: m+ Y5 K) U8 a3 b- V
9 O- M E" ~) Y: u( E3 j. r9 p2 R[ 本帖最后由 allen 于 2007-9-18 09:38 编辑 ] |
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