现代设计概述

Overview of Modern Digital Design Electronic circuit design has traditionally fallen into two main areas: analogue and digital. Within these two groupings there are further specializations, such as radio frequency analogue design; digital integrated circuit design; and, where the two domains meet, mixed-signal design. In addition, of course, software engineering plays an increasingly important role in embedded systems.

In the consumer electronic products, digital technology is more important. Automobile have complicated control system. Many families now also has a personal computer. Once considered simulation product radio, TV and phone in digital. Digital compact discs (CDS) almost completely replaced MiWen records (LP). These products appear makes product lifecycle shortened. In less than a year, the design of the nearby shops in the original products might be completely by the new digital electronic product substitution.

Design automation

In order to follow such rapid change, electronic products must with great speed design out. Simulation design is still a high degree, specialized lucrative professions. While digital design has been very dependent on computer aided design (CAD) - also called design automation (DA) or electronic design automation (EDA). EDA tools can complete comprehensive and simulation these two types of tasks. Synthesis is will design indexes into actual design, and simulation is realized for the realization of the indicator, or detailed design schemes for the exercise to ensure their normal operation.

Used for comprehensive and simulation EDA tools required designers will idea converts design. This can be drawn by using graphical package design principle diagram to achieve. This design method called principle diagram input. Another method is to use text form to say, this method and design of software programming and similar. For digital circuit hardware text describing can use a programming language, also can use hardware description language (HDL). In the past 30 years, designed around several HDL. Verilog and VHDL is two widely used hardware description

language. Standardization HDL is very important because of standardized language can be different producers to provide different CAD tools use. In Verilog and VHDL there before each CAD tools have their own HDL. Convert in different between HDL is slow and arduous.

Logic gates

A gate is the basic constitutes a digital circuit module. A gate is input and output by several composed of electronic devices. Normally, the input and output is logic 0 and logic 1 this one of two states. Logic values can be expressed by voltage or current. A gate using all output of a logic operation to produce output. Of course, digital gate after all is simulator pieces. Nevertheless, for the sake of simplicity, we tend to ignore simulation essence.

Mass production integrated circuit has integrated more and more complex function. The complexity of the increasing improvement of brings flexibility - microprocessors through programming can be finished almost unlimited kind of task. Therefore, some digital system design process is choice standard components, will its joined up. However, the standard components may not be able to provide a certain function, this is to avoid. Designers have to choose division gate to implement this function, or design application-specific integrated circuit to implement this function. Design special integrated circuit perhaps another man flinch, but don't forget - the system costs depend largely on device interconnection cost, rather than a single device cost.

Application-specific integrated circuits (ASICs) and field programmable gates array (FPGAs)

High-performance full customization integrated circuit design is a very difficult job. In all the custom integrated circuit design, all things need to design. However, using the gate arrays tectonic half customization integrated circuit for many years. As the name suggests, gate array is integrated the logic gate arrays integrated circuits. So, use gate array (application-specific integrated circuit design is to define the ASIC) the connection between the gate array. From realizing perspective, is to design a layer or two layers of metal interconnect. IC

manufacturing process is divided into seven steps, remove the last step metallization, other steps outside can be fulfilled ahead of time. Due to the gate arrays can produce lots, so a single device cost is lower.

ASIC usually refers to full customization and half customization integrated circuit. Programmable logic is another kind of integrated circuits. The earliest of programmable logic devices (PLD) is programmable logical array (PLA). And gate array, the PLA is by function as the array of undetermined logic. The plaaf and mask programming with is the difference between gate array of PLA for large voltage can be configured.

Design flow

Digital systems are mostly the timely, namely system existing state, output depends on now state. Some of the computer design is early, namely the asynchronous to input stabilized new status transfer. Tomorrow the Internet will create more miracles.many years. The synchronous system, change in state by one or more when the clock signal to design reliable triggered the system, people define the standard design method. Digital system design by division gate, can proceed as follows.

1. Write design specifications.

2. If necessary, will design is decomposed into several small, not every part of the design specifications write.

3. According to the design specifications, draw the state machine conversion figure. Displays in every state, containing system caused by change status each input conditions and the output of each state.

4. Will state for minimized. This is an optional steps, not in all cases are useful.

5. For each state distribution Boolean variables.

6. Deduced logic. Logic and output minor state

7. Normal logic and output logic of times optimization, which will be needed to minimize the number of the door.

8. Choose for logic gate reasonable layout, namely the integrated circuit contains what logic gates and the various integrated circuit in printed circuit board

position.

现代数字设计概述

传统上，数字电路设计可分为模拟设计、数字设计两大类。这两类设计还可以进行专业细分。例如，射频模拟电路设计、数字集成电路设计和混合电路设计。此外，在嵌入式系统设计中，软件工程设计师也扮演着越来越重要的角色。

在消费类电子产品中，数字电子技术更加重要。汽车拥有复杂的控制系统。许多家庭如今也拥有了个人电脑。曾被视为模拟产品的收音机、电视机和电话也都在数字化。数字光盘(CD)差不多完全替代了密纹唱片(LP)。这些产品的出现使得产品的生命周期缩短了。在不到一年的设计里，附近商店里的原有产品很可能就完全被新型数字电子产品替代了。

设计自动化

为了紧跟如此迅速的变化，电子产品必须要以极快的速度设计出来。模拟设计依然是专业化程度很高、收入颇丰的职业之一。而数字设计已经非常依赖计算机辅助设计（CAD）—又称设计自动化（DA）或电子设计自动化（EDA）。EDA工具可完成综合和模拟这两类任务。综合是将设计指标转变为实际的设计实现，而模拟是对设计指标或详细的实现方案进行演习，以确保其正常运行。

用于综合和模拟的EDA工具要求设计者将想法转换成设计。这可以通过使用图形化软件包绘制设计原理图来实现。这种设计方法称为原理图输入。另一种方法是用文本形式来表示设计，这种方法和软件编程和相似。对数字电路硬件的文本描述可以采用编程语言，也可以采用硬件描述语言（HDL）。在过去约30年中，设计出了几种HDL。V erilog和VHDL是两种广泛应用的硬件描述语言。标准化HDL是很重要的，因为标准化语言可以被不同生产商提供的不同CAD工具使用。在V erilog和VHDL出现之前，每个CAD工具都有自己的HDL。在不同HDL之间进行转换即费时又费力。

逻辑门

门电路是构成数字电路的基本模块。门电路是由几个输入和一个输出组成的电子器件。在通常情况下，输入和输出是逻辑0和逻辑1这两个状态之一。逻辑值可以由电压或电流来表示。门电路利用全部输出实现某种逻辑操作以产生输出。当然，数字门电路说到底也是模拟器件。不过，为了简便起见，我们倾向于忽略模拟本质。

大规模生产的集成电路集成了越来越多的复杂功能。日益增加的复杂度带来了灵活性的提高—微处理器通过编程可以完成几乎无限种任务。因此，某些数字系统的设计过程就是选

择标准元器件、将其连接起来。不过，标准元器件可能无法提供某种功能，这是避免不了的。设计者只好选用分立门电路来实现这种功能，或者设计专用集成电路来实现这种功能。设计专门集成电路或许另人畏缩，但不要忘记—系统成本在很大程度上取决于器件互连成本、而非单个器件成本。

专用集成电路(ASICs)和现场可编程门阵列(FPGAs)

高性能全定制集成电路设计是一项难度很大的工作。在全定制集成电路设计中，所有事情都需要设计。不过，利用门阵列构造半定制集成电路已有多年。顾名思义，门阵列就是集成了逻辑门阵列的集成电路。所以，使用门阵列设计专用集成电路（ASIC）就是要定义阵列中的门电路之间的连接。从实现角度看，就是要设计一层或两层的金属互连线。集成电路的制造流程分为七个步骤，除去最后一步金属化之外，其他步骤都可提前完成。由于门阵列可以大量生产，所以单个器件成本就比较低。

ASIC通常是指全定制和半定制集成电路。可编程逻辑是另外一类集成电路。最早的可编辑逻辑器件（PLD）是可编程逻辑阵列（PLA）。和门阵列一样，PLA也是由功能待定逻辑组成的阵列。PLA和掩膜编程门阵列的区别是用大电压可以对PLA进行配置。

设计流程

数字系统大多是时序的，即系统存在各种状态，输出取决于现态。早期的某些计算机设计是异步的，即输入稳定下来后就向新状态转移。数字系统的同步设计趋势已经有多年了。在同步系统中，状态的改变时由一个或多个时钟信号触发的，为了设计可靠的系统，人们定义了规范的设计方法。采用分立门电路设计数字系统，可按如下步骤进行。

1.写出设计规格。

2.如果需要的话，将设计分解为若干个小部分，并未每一部分写出设计规格。

3.根据设计规格，画出状态机转换图。该图包含系统中的每个状态、引起状态变化的

每个输入条件和每个状态的输出。

4.将状态数最小化。这是一个可选步骤，并不是在所有情况下都有用。

5.为每个状态分配布尔变量。

6.推导出次态逻辑和输出逻辑。

7.对次态逻辑和输出逻辑进行优化，从而将所需的门数量减至最小。

8.为逻辑门选择合理的布局，即集成电路中包含哪些逻辑门以及各个集成电路在印制

电路板上的位置。