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INTRODUCTION5 q( h/ ?+ h* u! G) `
The most important factor in the design of many systems today is speed. 66-MHz thru 200-MHz* N M2 m; i7 V; w
processors are common; 233 and 266-MHz processors are becoming readily available. The demand
) {* K. {# `4 t1 s% G" bfor high speed results from: a) the requirement that systems peRForm complex tasks in a time frame
& g" d% O- X8 h7 f/ H' \considered comfortable by humans; and b) the ability of component manufacturers to produce
! t! g7 {; n$ K; O& u! X/ I7 C4 Whigh-speed devices. An example of a) is the large amount of information that must be processed
7 R/ R5 b) _. T8 t. ]; Z9 Dto perform even the most rudimentary computer animation. Currently, Programmable Array Logic# Y8 g% B0 e( U0 v7 j
(PAL®) devices are available with propagation delays of 4.5 ns, and complex PLDs such as MACH6 W0 ]$ F9 L! \
®have propagation delays of 5 ns. While this might seem fast, it is not the propagation delay that' x( Z2 t$ b& U ~8 @3 q' Q) L K3 P
creates the potential for problems, but rather the fast edge rates needed to obtain the fast
& B# S) ?+ i I( g+ }propagation delays. In the future, much faster devices will become available, with correspondingly
- X+ S9 ~1 q& ^faster edge rates.
8 S0 M6 }. o. O4 o; @- JDesigning high-speed systems requires not only fast components, but also intelligent and careful+ I9 z" K2 i; o1 p: v5 D' {3 ?
design. The analog aspect of the devices is as important as the digital. In high-speed systems, noise% o& b1 j p* j3 V: V2 D
generation is a prime concern. The high frequencies can radiate and cause interference. The
; o/ J; T8 z& l) h4 ~corresponding fast edge rates can result in ringing, reflections, and crosstalk. If unchecked, this+ q3 _. q; T1 m- J; _% G
noise can seriously degrade system performance.
: ~7 W5 }1 P& b$ ~. W# H% Q8 g2 W5 V1 N5 m
[ 本帖最后由 allen 于 2007-9-18 09:38 编辑 ] |
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