工程师故事：让人又爱又恨的参考设计

(电子工程专辑版权)一开始，就有诸如经典的IC定时器(衍生出传说中的555定时器IC)这样的电路“食谱”。典型的电路“食谱”也即范例电路，有几十个基本的电原理图，每一个电路解决一个特定的、简单的问题或目标。例如“带可变超时功能的电子锁”。

大多数这类型的范例电路都有原理图、材料清单(BOM)、对电路功能和行为的简单描述，但是没有版图和性能分析。更甚者这其中的许多范

例设计实际上根本就不成立(我敢肯定你一定惊呆了！)，这些范例电路我们礼貌性的称为“理论设计(speculative design)”。

这些范例电路虽然简洁，但仍然是点子的好来源，以及其他电路的出发点。它们简单，同时，也是其弱点：如果你想或是需要对这些电路

做出一些修改，又或是要加上自己设计的一部分，那可能就难了。因为你经常不足以解释电路的精妙之处，也无法了解哪一部分是至关重要的

而哪一部分不是，哪一部分是可以改动的而哪一部分又必须“如图所示”。工程师和实验电路(一个多种多个)之间的状况经常是：“我需要它，我喜欢它，它让我抓狂，我不明白为什么它不工作，我要做更多……”

然而，现在工程师的需求要多得多。供应商也不可能没有全局的参考设计而推出一个新的部件，甚至是诸如运放之类的基本模块。这些设计进行了许多改善之后远比范例电路要好得多，包括PCB版图、性能曲线、验证该设计确实成立的图片，Spice或其他模式的仿真，电路行为、关键部件、驱动软件和验证软件的作用的描述等。

这些参考设计一举数得：可以加快项目上市的时间，减少再设计周期的需要，对供应商最重要的是，可以证明这一部件确实可以满足其正确的版图的标准，当用户说“你的部件没有符合规范”是个好的先发制人的回答。

到目前为止，一切都很美好。但是在许多工程师的心中，参考设计的问题是，他们也许太美好了。毕竟，如果一个微调好的参考设计摆在那的话。谁还需要一个熟练的工程师来设计电路和其版图呢？而且如果项目团队和竞争对手都采用了相同的参考设计，那竞争力又体现在哪里呢？工程师的角色变成减少系统集成，软件，还是封装？

当工程师们的灵活性和想法都消失怠尽时，参考设计对努力工作思考到最后一刻的设计师来说算得上是好消息了。如果是一个可靠的参考设计，将会引导你从一个已知的工作电路开始，版图布局，BOM清单，然后做出一些改变和选择来更适合自己项目重点。但如果是不合格的参考设计，可能会将你引入歧途，或进行某些不必要的限制，或者让你陷入在“幸福的”无知里而事与愿违。你使用参考设计的经历如何？你的立场又是什么，爱，恨，接受或是拒绝参考设计？你曾经被哪个参考设计误导甚至被骗过吗？不妨来分享下你的故事。

点击参考原文：

Why engineers love/hate; embrace/shun reference designs

编译：Aileen Zhu

《电子工程专辑》网站版权所有，谢绝转载

{pagination}

Why engineers love/hate; embrace/shun reference designs

Bill Schweber

In the beginning, there was the circuit "cookbook" such as the classic IC Timer Cookbook for the legendary 555 timer IC. The typical cookbook had dozens of basic schematics, each solving a specific, simple problem or objective, such as "Electronic lock has variable timeout".

Most cookbooks included a circuit schematic, bill of materials, and a short description of the circuit function and operation, but had no layout or performance analysis. Further, many of these cookbook designs had not actually been built (I'm sure you are shocked!), but were based on what we'll call politely "speculative design."

Despite their brevity, these cookbook circuits were—and still are—a good source of ideas and starting points for other circuits. Their simplicity, though, is also their weakness: if you wanted or needed to modify the circuit to do something different, or to use the parts you had available, that could be difficult: you often didn't have enough explanation of the operational subtleties to understand what was critical, what was not, what could be changed, and what had to remain as shown. The relationship between the engineer or circuit experimenter was often (pick one or more): "I need it, I like it, it's driving me crazy, I don’t understand why it doesn't work, I need it to do more."

But engineers today demand much more. Now, a vendor can't announce a new part, even a basic building block such as an op amp, without a full-on reference design. These designs go well beyond the cookbook by proving lots of information, including PCB layout, performance curves, photos to verify that the design was actually built, Spice and other models, a description of the operation and the role of key components, driver software, and validation software.

These reference designs serve several purposes: they speed the project's time to market, reduce the need to re-invent the design wheel, and—important for the vendor--shows that the part actually can meet its specifications with the right layout. They are a pre-emptive answer to the user saying "your part doesn’t meet its spec."

So far, so good. But in the mind of many engineers, the problem with reference designs is that they are perhaps too good. After all, who needs a skilled engineer to design and lay out a circuit, when that fine-tuned reference design is waiting there? And if the project team and its competitors all have access to that same reference design, what's the competitive edge going to be? Is the engineers' role reduced to system integration, software, and packaging?

At the same time, reference designs themselves have changed and improved. Some, like the Webench family from National Semiconductor Corp. (click here), allow the engineer to use interactive online tools to adjust circuit parameters and tradeoffs, to find a circuit configuration which hits the "sweet spot" among conflicting goals of performance, power and efficiency, and pricing for the ICs and their associated passive components.

The latest reference design tool goes in a somewhat different direction. Their just-announced Circuits from the Lab from Analog Devices (click here and here for a pair of overviews) starts with a reference design, then adds detailed circuit tutorial, FAQs, PCB details, and more, all rolled together. It addresses both the "how?" and "what if?" of the topology and circuit details.

Reference designs are mostly good news for the hard-working, deadline-constrained designer, when they are done with flexibility and insight. If they are from a reputable source, they let you start with a known working circuit, layout, and BOM, and then make the changes and choices you need to better meet your project priorities. But one from a less-than-qualified source can lead you astray or constrain you unnecessarily, or trap you in blissful ignorance that backfires.

What's been your experience with reference designs? Where do you stand in terms of loving, hating, embracing, or shunning them? And have you ever been misled or even "burned" by one?