實際上，每個產品設計必須經歷數字提取和真實模擬世界。設計前期的一些考慮將焦點放在接口設計上。
20世紀后半葉的技術創(chuàng)新達到空前的速度。不像以前，這個時期的許多進步很快應用到廣泛的消費市場。直到那個時候，因為我們的社會趨向于從消費者利益中榨取全部價值和壽命，商人需要對新產品產生足夠興趣，引起顧客轉變進一步需要：這是可任意使用經濟的起源。
19世紀50年代開始，廣告使用例如“噴氣時代”、“原子時代”和“空間時代”的習語，將產品連接到顯現和快速
改變現代性的社會映像。諷刺地，這些習語也許都沒有剩下的一個有力量：“數字時代”。19世紀70年代開始，時代恰好表明關聯事物不是簡單的現代，而與早期產品有明顯不同。
確實，數字提取改革了我們的工業(yè)、幾乎每個經濟部門和所有生活的方面。雖然結果相當真實，但這個提取嚴格的說只是概念上的。結果，事實上每個產品設計必須從數字抽取橋接到真實模擬世界。
需求的東西明顯瑣碎：IC布局考慮、IC和PCB之間接口、PCB的布版、到箱子遠處點的產品接口、系統(tǒng)箱和系統(tǒng)網絡，所有都必須處理本質相似的接口關系。不管這些條目，這個檢查保持了非常不同的范圍，跨越了多于10階的量級。事實是，雖然接口挑戰(zhàn)了帶寬的增長，問題卻通過頻譜出現了。
早期設計階段的一些考慮著眼于接口設計。接口瑣碎特性的結果是在產品定義階段就開始詳述接口需求，在結構圖、原理圖和仿真階段改進。
我區(qū)別反復設計改進的過程——有目的地改進設計過程和反復設計一系列修改。產品定義階段的第一個關口應該建立對接口價格、復雜性和設計時間的粗略估計。第一階段的輸出在圖表階段作為執(zhí)行定型的檢查。從前兩個階段，不同價格或復雜性估計作為對三個條件中一個的警告：
接口設計影響加工。
第一階段未能合理計算所有產品定義需求。
改變產品定義浪費了費用和復雜性估計，這些估計需要更新工程管理行為的部分。
在后來的設計階段，做相似的檢查。
作為階段一的起始點，記住每個接口的信號源、線和客戶端的特性。不管信號的“數字”意義，記住接口動作是模擬和多參數的?？紤]每條線帶寬的需求，源阻抗、信號幅值和運行長度；連接媒介的特征；噪聲源或干擾的存在，所有前后接收端電路信號的保真需求。在仿真階段，比較最壞情況下發(fā)送和接收端波形?？紤]前后信號調理技術，改進不足。如果延遲這些檢查到原型估價，也許將改進設計滑到反復設計，需要更多花費。
英文原文：
Building bridges: Specifying and refining inteRFace designs
Virtually every product design must bridge the digital abstraction and the real analog world. A few considerations early in the design phase can focus an interface design.
By Joshua Israelsohn, Contributing Technical Editor -- EDN, 11/8/2007
Technological innovation during the second half of the 20th century came at an unprecedented pace, and, unlike earlier times, many advances during this interval moved rapidly into the broad consumer market. Because our society, until that time, tended to wring the full value and lifetime from a consumer good, marketers needed to generate sufficient excitement for new products to cause customers to switch in advance of necessity: the origin of the disposable economy.
Indeed, the digital abstraction has revolutionized our industry, almost every sector of our economy, and all but a few aspects of our lives. Though the effects have been quite real, this abstraction is, as all are, strictly conceptual. As a
result, virtually every product design must bridge the digital abstraction and the real analog world.
This requirement is remarkably fractal-like: Layout considerations within an IC, the inteRFace between an IC and its PCB, the PCB's layout, the product interface to points beyond the box, systems of boxes, and networks of systems all must contend with essentially similar interface concerns. This observation holds despite these items' enormously different scales, which can span more than 10 orders of magnitude. It is also the case that, though interface challenges grow with bandwidth, the issue arises throughout the spectrum.
A few considerations early in the design phase can focus an interface design. A consequence of the fractal-like traits of interfaces is that you can begin specifying interface requirements at the product-definition phase and refine them at the block-diagram, schematic, and simulation phases.
I distinguish this process of design refinement from iterative design—design refinement being a purposeful process of design in phases, and iterative design being a sequence of design repairs. The first pass at the product-definition phase should allow you to establish a good rough estimate for an interface's cost, complexity, and design time. The first phase's output can serve as your check as an implementation takes shape at the block-diagram phase. Disparities in cost or complexity estimates from the first and second phases serve as warnings against one of three conditions:
The interface design is heading off into the toolies.
The first phase failed to account properly for all product-definition requirements.
Changes to the product definition have made obsolete the cost and complexity estimates, and these estimates require updating as part of your project-management activities.
Make similar checks at subsequent design phases.
As a phase-one starting point, bear in mind the signal-source, -line, and -client attributes for each interface. Despite your signal's “digital” significance, remember that interface behaviors are analog and multiparametric. Take into account each line's bandwidth requirement, source impedance, signal magnitude, and run length; the characteristics of the connecting media; and the presence of noise sources or interferers, all in the context of the receiver-side circuit's signal-fidelity requirements. In the simulation phase, compare the transmitter- and receiver-side waveforms under the worst-case combination of these measures. Consider pre- and post-signal-conditioning techniques to correct deficiencies. If you delay these observations until prototype evaluation, you may slip from design refinement into a more costly course of iterative design.
英文原文地址：http://www.edn.com/article/CA6495304.html
發(fā)布者：博子
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