Integrated_Circuits(集成电路)电子信息类专业英语、计算机类专业英语-20页文档资料

1、Integrated Circuits(集成电路 )第 19 页The Integrated CircuitDigitallogic and electronic circuits derive theirfunctionality from electronic switches called transistor. Roughlyspeaking, the transistor can be likened to an electronically controlled valve whereby energy applied to one connection of thevalve e

2、nables energy to flow between two other connections.By combining multiple transistors, digital logic building blocks such as AND gates and flip-flops are formed. Transistors, in turn, aremade from semiconductors. Consult a periodic table of elements ina college chemistry textbook, and you will locat

3、e semiconductorsas a group of elements separating the metals and nonmetals.They are called semiconductors because of their ability to behave as bothmetals and nonmetals. A semiconductor can be made to conduct electricity like a metal or to insulate as a nonmetal does. Thesediffering electrical prope

4、rties can be accurately controlled bymixing the semiconductor with small amounts of other elements. Thismixing is called doping. A semiconductor can be doped to containmore electrons (N-type) or fewer electrons (P-type). Examples ofcommonly used semiconductors are silicon and germanium. Phosphorous

5、and boron are two elements that are used to dope N-type and P-type silicon, respectively.A transistor is constructed by creating a sandwich of differently doped semiconductor layers. The two most common typesof transistors, the bipolar-junction transistor (BJT) and the field-effect transistor (FET)

6、are schematically illustrated in Figure 2.1.This figure shows both the silicon structures of these elements and their graphical symbolic representation as would beseen in a circuit diagram. The BJT shown is an NPN transistor, because it is composed of a sandwich of N-P-N doped silicon. When a small

7、current is injected into the base terminal, a larger current is enabled to flow from the collector to the emitter.The FET shownis an N-channel FET, which is composed of two N-type regions separated by a P-type substrate. When a voltage is applied to theinsulated gate terminal, a current is enabled t

8、o flow from the drain to the source. It is called N-channel, because the gate voltageinduces an N-channel within the substrate, enabling current to flow between the N-regions.Another basic semiconductor structure is a diode, which is formed simply by a junction of N-type and P-type silicon. Diodesac

9、t like one-way valves by conducting current only from P to N.Special diodes can be created that emit light when a voltage isapplied. Appropriately enough, these components are called lightemitting diodes, or LEDs. These small lights are manufactured bythe millions and are found in diverse applicatio

10、ns from telephones to traffic lights.The resulting small chip of semiconductor material on which a transistor or diode is fabricated can be encased in a small plastic package for protection against damage and contamination from the out-side world.Small wires are connected within this package between

11、 the semiconductor sandwich and pins that protrude from the package to makeelectrical contact with other parts of the intended circuit. Once you have several discrete transistors, digital logic can be built by directly wiring these components together. The circuit will function, but any substantial

12、amount of digital logic will be very bulky, because several transistors are required to implement each of the various types of logic gates.At the time of the invention of the transistor in 1947 byJohn Bardeen, Walter Brattain, and William Shockley, the only way to assemble multiple transistors into

13、a single circuit was to buy separate discrete transistors and wire them together. In 1959, Jack Kilby and Robert Noyce independently invented a meansof fabricating multiple transistors on a single slab of semiconductor material.Their invention would come to be known as the integrated circuit, or IC,

14、 which is the foundation of our modern computerized world. An IC is so called because it integrates multiple transistors anddiodes onto the same small semiconductor chip. Instead of havingto solder individual wires between discrete components, an IC contains many small components that are already wi

15、red together in the desired topology to form a circuit.A typical IC, without its plastic or ceramic package, isa square or rectangular silicon die measuring from 2 to 15 mm on an edge. Depending on the level of technology used to manufacture the IC, there may be anywhere from a dozen to tens of mill

16、ions of individual transistors on this small chip. This amazing density of electronic components indicates that the transistors and the wires that connect them are extremely small in size. Dimensions on an IC are measured in units of micrometers, with one micrometer (1mm) being one millionth of a me

17、ter. To serve as a reference point, ahuman hair is roughly 100mm in diameter. Some modern ICs contain components and wires that are measured in increments as small as 0.1mm! Each year, researchers and engineers have been finding new ways to steadily reduce these feature sizes to pack more transistor

18、s into the same silicon area, as indicated in Figure 2.2.When an IC is designed and fabricated, it generally follows one of two main transistor technologies: bipolar or metal-oxide semiconductor (MOS). Bipolar processes create BJTs, whereas MOS processes create FETs. Bipolar logic was more common be

19、fore the1980s, but MOStechnologies have since accounted the great majority of digital logic ICs. N-channel FETs are fabricated in an NMOS process, and P-channel FETs are fabricated in a PMOS process. In the 1980s, complementary-MOS, or CMOS,became the dominant process technology and remains so to th

20、is day. CMOS ICs incorporate both NMOS and PMOS transistors.Application Specific Integrated CircuitAn application-specific integrated circuit (ASIC) is an integrated circuit (IC) customized for a particular use, rather than intended for general-purpose use. For example, a chip designed solely to run

21、 a cell phone is an ASIC. In contrast, the 7400 series and 4000 series integrated circuits are logic building blocks that can be wired together for use in many different applications.As feature sizes have shrunk and design tools improved over the years, the maximum complexity (and hence functionalit

22、y) possible in an ASIC has grown from 5,000 gates to over 100 million.Modern ASICs often include entire 32-bit processors, memory blocks including ROM, RAM, EEPROM, Flash and other large building blocks. Such an ASIC is often termed a SoC (System-on-Chip). Designers of digital ASICs use a hardware d

23、escription language (HDL), such as Verilog or VHDL, to describe the functionality of ASICs.Field-programmable gate arrays (FPGA) are the modern dayequivalent of 7400 series logic and a breadboard, containing programmable logic blocks and programmable interconnects that allow the sameFPGAto be used i

24、n many different applications. For smaller designs and/or lower production volumes, FPGAs may be more cost effective than an ASIC design. The non-recurring engineering cost (the cost to setup the factory to produce a particular ASIC) can run into hundreds of thousands of dollars.The general term app

25、lication specific integrated circuit includes FPGAs, but most designers use ASIC only for non-field programmable devices and make a distinction between ASIC and FPGAs.HistoryThe initial ASICs used gate array technology. Ferranti produced perhaps the first gate-array, the ULA (Uncommitted Logic Array

26、), around 1980. Customization occurred by varying the metal interconnect mask. ULAs had complexities of up to a few thousand gates. Later versions became more generalized, with different base dies customized by both metal and polysilicon layers. Somebase dies include RAM elements.Standard cell desig

27、nIn the mid 1980s a designer would choose an ASIC manufacturer and implement their design using the design tools available from the manufacturer. While third party design tools were available,there was not an effective link from the third party design tools to the layout and actual semiconductor pro

28、cess performance characteristics of the various ASIC manufacturers.Most designers ended up using factory specific tools to complete the implementation of their designs. A solution to this problem that also yielded a muchhigher density device was the implementation of Standard Cells. Every ASIC manuf

29、acturer could create functional blocks with known electrical characteristics, such as propagation delay, capacitance and inductance; that could also be represented in third party tools.Standard cell design is the utilization of these functional blocks to achieve very high gate density and good elect

30、rical performance. Standard cell design fits between Gate Array and Full Custom design in terms of both its NRE (Non-Recurring Engineering) and recurring component cost.By the late 1980s, logic synthesis tools, such as Design Compiler, became available. Such tools could compile HDL descriptions into

31、 a gate-level netlist. This enabled a style of design called standard-cell design. Standard-cell Integrated Circuits (ICs) are designed in the following conceptual stages, although these stages overlap significantly in practice.These steps, implemented with a level of skill common in the industry, a

32、lmost always produce a final device that correctly implements the original design, unless flaws are later introduced by the physical fabrication process.A team of design engineers starts with a non-formal understanding of the required functions for a new ASIC, usually derived from requirements analy

33、sis.*The design team constructs a description of an ASIC to achieve these goals using an HDL. This process is analogous to writing a computer program in a high-level language. This is usually called the RTL (register transfer level) design.*Suitability for purpose is verified by simulation. A virtua

34、lsystem created in software, using a tool such as Virtutech s Simics, can simulate the performance of ASICs at speeds up to billions of simulated instructions per second.*A logic synthesis tool, such as Design Compiler, transforms the RTL design into a large collection of lower-level constructs call

35、ed standard cells. These constructs are taken from a standard-cell library consisting of pre-characterized collectionsof gates such as 2 input nor, 2 input nand, inverters, etc.The standard cells are typically specific to the planned manufacturer of the ASIC. The resulting collection of standard cel

36、ls, plus the needed electrical connections between them, is called a gate-level netlist.*The gate-level netlist is next processed by a placementtool which places the standard cells onto a region representing the final ASIC. It attempts to find a placement of the standard cells, subject to a variety

37、of specified constraints. Sometimes advancedtechniques such as simulatedannealing are used to optimizeplacement.*The routing tool takes the physical placement of the standard cells and uses the netlist to create the electrical connectionsbetween them. Since the search space is large, this process wi

38、llproduce a “sufficient” rather than “globally - optimal ” solution.The output is a set of photomasks enabling semiconductor fabrication to produce physical ICs.*Close estimates of final delays, parasitic resistances andcapacitances, and power consumptions can then be made. In the caseof a digital c

39、ircuit, this will be further mapped into delay information. These estimates are used in a final round of testing.This testing demonstrates that the device will function correctlyover all extremes of the process, voltage and temperature. Whenthis testing is complete the photomask information is relea

40、sed for chip fabrication.These design steps (or flow) are also commonto standard product design. The significant difference is that Standard Cell design uses the manufacturer s cell libraries that have been used in hundreds of other design implementations and therefore are of muchlower risk than ful

41、l custom design.Gate array designGate array design is a manufacturing method in which the diffused layers, i.e. transistors and other active devices, are predefined and wafers containing such devices are held in stock prior to metallization, in other words, unconnected.The physicaldesign process the

42、n defines the interconnections of the final device. It is important to the designer that minimal propagation delays can be achieved in ASICs versus the FPGA solutions available in the marketplace. Gate array ASIC is a compromise as mapping a given design onto what a manufacturer held as a stock wafe

43、r never gives 100% utilization.Pure, logic-only gate array design is rarely implemented bycircuit designers today, replaced almost entirely by field programmable devices such as FPGAs, which can be programmed by the user and thus offer minimal tooling charges, marginally increased piece part cost an

44、d comparable performance.Today gate arrays areevolving into structured ASICs that consist of a large IP core like a processor, DSPunit, peripherals, standard interfaces, integrated memories SRAM,and a block of reconfigurable uncommitted logic.Thisshift is largely because ASIC devices are capable of

45、integrating such large blocks of system functionality and“ system on a chip ”requires far more than just logic blocks.Full-custom designThe benefits of full-custom design usually include reduced area, performance improvements and also the ability to integrate analog components and other pre-designed

46、 components such as microprocessor cores that form a System-on-Chip. The disadvantages can include increased manufacturing and design time, increased non-recurring engineering costs, more complexity in the CAD system and a much higher skill requirement on the part of the design team.However for digi

47、tal only designs,“standard - cell ” libraries together withmodern CADsystems can offer considerable performance/cost benefits with low risk. Automated layout tools are quick and easy to use and also offer the possibility to manually optimize any performance limiting aspect of the design.Structured d

48、esignStructured ASIC design is an ambiguous expression, with different meanings in different contexts. This is a relatively new term in the industry, which is why there is some variation in its definition. However, the basic premise of a structured ASIC is that both manufacturing cycle time and desi

49、gn cycle time are reducedcompared to cell-based ASIC by virtue of there being pre-defined metal layers and pre-characterization of what is on the silicon.One definition states that, in a structured ASIC design, the logic mask-layers of a device are predefined by the ASIC vendor (or in some cases by

50、a third party). Structured ASIC technology is seen as bridging the gap between field-programmable gate arrays and “standard - cell ” ASIC designs.What makes a structured ASIC different from a gate array is that in a gate array the predefined metal layers serve to make manufacturing turnaround faster

51、. In a structured ASIC the predefined metallization is primarily to reduce cost of the mask sets and is also used to make the design cycle time significantly shorter as well.Likewise, the design tools used for structured ASIC can substantially lower cost, and are easier to use than cell-based tools,

52、 because the tools do not have to perform all the functions that cell-based tools do.One other important aspect about structured ASIC is that it allows IP that is commonto certain applications to be “built in ” , rather than “designed in ” . By building the IP directly into the architecture the desi

53、gner can again save both time and money compared to designing IP into a cell-based ASIC.中文翻译:集成电路数字逻辑和电子电路由称为晶体管的电子开关得到它们的（各种）功能。粗略地说，晶体管好似一种电子控制阀，由此加在阀一端的能量可以使能量在另外两个连接端之间流动。通过多个晶体管的组合就可以构成数字逻辑模块，如与门和触发电路等。而晶体管是由半导体构成的。查阅大学化学书中的元素周期表，你会查到半导体是介于金属与非金属之间的一类元素。它们之所以被叫做半导体是由于它们表现出来的性质类似于金属和非金属。可使半导体像金属

54、那样导电，或者像非金属那样绝缘。通过半导体和少量其它元素的混合可以精确地控制这些不同的电特性，这种混合技术称之为“半导体掺杂” 。半导体通过掺杂可以包含更多的电子（ N 型）或更少的电子（ P 型） 。 常用的半导体是硅和锗， N 型硅半导体掺入磷元素，而 P 型硅半导体掺入硼元素。不同掺杂的半导体层形成的三明治状夹层结构可以构成一个晶体管，最常见的两类晶体管是双极型晶体管（BJT）和场效应晶体管（FED ,图2.1 给出了它们的图示。图中给出了这些晶体管的硅结构，以及它们用于电路图中的符号。BJT是NPN晶体管，因为由Nr-P N掺杂硅三层构成。当小电流注入基极时，可使较大的电流从集电极流向

55、发射极。图示的 FET是 N 沟道的场效应型晶体管，它由两块被P 型基底分离的 N 型组成。将电压加在绝缘的栅极上时，可使电流由漏极流向源极。它被叫做N 沟道是因为栅极电压诱导基底上的N通道，使电流能在两个 N区域之间流动。另一个基本的半导体结构是二极管，由 N 型和 P 型硅连接而成的结组成。二极管的作用就像一个单向阀门，由于电流只能从P流向No可以构建一些特殊二极管，在加电压时可以发光，这些器件非常合适地被叫做发光二极管或LEQ这种小灯泡数以百万计地被制造出来，有各种各样的应用，从电话机到交通灯。半导体材料上制作晶体管或二极管所形成的小芯片用塑料封装以防损伤和被外界污染。在这封装里一些短线

56、连接半导体夹层和从封装内伸出的插脚以便与（使用该晶体管的）电路其余部分连接。一旦你有了一些分立的晶体管，直接用电线将这些器件连线在一起就可以构建数字逻辑（电路） 。电路会工作，但任何实质性的数字逻辑（电路）都将十分庞大，因为要在各种逻辑门中每实现一种都需要多个晶体管。1947 年， John Bardeen 、 Walter Brattain 和 and William Shockley发明晶体管的时候。将多个晶体管组装在一个电路上的唯一方法就是购买多个分离的晶体管，将它们连在一起。 1959 年， Jack Kilby 和 RobertNoyce 各自独立地发明了一种将多个晶体管做在同一片半

57、导体材料上的方法。这个发明就是集成电路，或IC ，是我们现代电脑化世界的基础。集成电路之所以被这样命名，是因为它将多个晶体管和二极管集成到同一块小的半导体芯片上。 IC 包含按照形成电路所要求的拓扑结构连在一起的许多小元件，而无需再将分立元件的导线焊接起来。去除了塑料或陶瓷封装后，一个典型的集成电路就是每一边2mm至15mm勺方形或矩形硅片。根据制造集成电路的技术水平的不同，在这种小片上可能有几十个到几百万个晶体管，电子器件这种令人惊异的密度表明那些晶体管以及连接它们线是极其微小的。集成电路的尺寸是以微米为单位测量的， 1 微米是 1 米的百万分之一。作为参照，一根人的头发其直径大约为 100

58、 微米。一些现代集成电路包含的元件和连线，是以小到 0.1 微 米的增量来测量的。每年研究人员和工程师都在寻找新的方法来不断减小这些元件的大小，以便在同样面积的硅片上集成更多的晶体管，如图 2.2 所示。在集成电路的设计和制造过程中，常用两种主要晶体管技术是：双极和金属氧化物半导体（MOS。双极工艺生产出来的是 BJT（双极型晶体管）， 而MOST艺生产出来的是FET（场效应晶体管）。在20世纪80年代以前更 常用的集成电路是双极逻辑，但是此后MO茨术在数字逻辑集成电路中占据了大多数。N沟道FET是采用NMOSC艺生产的，而 P沟道FET是采用 PMOST艺生产白到了 20世纪80年代，互补 MOS1CMO破为占主导地 位的加工技术，并且延续至今。CMO集成电路包含了 NMO廊PMOS5种晶 体管。专用集成电路（ ASIC）专用集成电路（ASIC）是为了特殊应用而定制的集成电路，而不是通用的。比如，一片仅被设计用于运行蜂窝式电话的芯片是专用集成电路（ ASIC） 。 相比之下， 7400 与 4000 系列集成电路是可以用导线连接的逻辑构建模块，适用于各种不同的应用。随着逐年