Suppose further that the Japanese government convinces your largest importer the US, say to strengthen its currency to avert a further Japanese economic disaster, and that the prices of your export goods become relatively unattractive because your currency is pegged to the dollar. Your exports weaken, currency speculators see an opportunity to sell you short and bet against your currency until it cracks, your stock market crashes and you start defaulting on loans to your biggest creditor Japan, whose banking system was already insolvent anyway. That's the good news: Japanese banks go on cooking the books, so in the long run maybe you just default on some onerous loans and your credit rating takes a hit so capital becomes expensive.
An early successful commercial application was the gate array circuitry found in the low-end 8-bit ZX81 and ZX Spectrum personal computersintroduced in and Customization occurred by varying a metal interconnect mask.
Gate arrays had complexities of up to a few thousand gates; this is now called mid-scale integration. Later versions became more generalized, with different base dies customised by both metal and polysilicon layers. Some base dies include RAM elements. Standard cell In the mids, 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 process performance characteristics of the various ASIC manufacturers. Most designers used factory-specific tools to complete the implementation of their designs.
A solution to this problem, which also yielded a much higher density device, was the implementation of standard cells. Every ASIC manufacturer could create functional blocks with known electrical characteristics, such as propagation delaycapacitance 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 electrical performance. By the late s, logic synthesis tools became available. Such tools could compile HDL descriptions into a gate-level netlist.
Standard-cell integrated circuits ICs are designed in the following conceptual stages referred to as electronics design flowalthough these stages overlap significantly in practice: A team of design engineers starts with a non-formal understanding of the required functions for a new ASIC, usually derived from requirements analysis.
Register-transfer level RTL design: The design team constructs a description of an ASIC to achieve these goals using a hardware description language. This process is similar to writing a computer program in a high-level language. Suitability for purpose is verified by functional verification.
This may include such techniques as logic simulation through test benchesformal verificationemulationor creating and evaluating an equivalent pure software model, as in Simics. Each verification technique has advantages and disadvantages, and most often several methods are used together for ASIC verification.
Logic synthesis transforms the RTL design into a large collection called of lower-level constructs called standard cells. These constructs are taken from a standard-cell library consisting of pre-characterized collections of logic gates performing specific functions. The standard cells are typically specific to the planned manufacturer of the ASIC.
The resulting collection of standard cells and the needed electrical connections between them is called a gate-level netlist. The gate-level netlist is next processed by a placement tool which places the standard cells onto a region of an integrated circuit die representing the final ASIC.
The placement tool attempts to find an optimized placement of the standard cells, subject to a variety of specified constraints. An electronics routing tool takes the physical placement of the standard cells and uses the netlist to create the electrical connections between them.
The output is a file which can be used to create a set of photomasks enabling a semiconductor fabrication facilitycommonly called a 'fab' or 'foundry' to manufacture physical integrated circuits. Placement and routing are closely interrelated and are collectively called place and route in electronics design.
Given the final layout, circuit extraction computes the parasitic resistances and capacitances. In the case of a digital circuitthis will then be further mapped into delay information from which the circuit performance can be estimated, usually by static timing analysis.
This, and other final tests such as design rule checking and power analysis collectively called signoff are intended to ensure that the device will function correctly over all extremes of the process, voltage and temperature.
When this testing is complete the photomask information is released for chip fabrication. These steps, implemented with a level of skill common in the industry, almost always produce a final device that correctly implements the original design, unless flaws are later introduced by the physical fabrication process.
The significant difference is that standard-cell design uses the manufacturer's cell libraries that have been used in potentially hundreds of other design implementations and therefore are of much lower risk than full custom design.
Standard cells produce a design density that is cost effective, and they can also integrate IP cores and static random-access memory SRAM effectively, unlike gate arrays. Gate-array and semi-custom design[ edit ] Microscope photograph of a gate-array ASIC showing the predefined logic cells and custom interconnections.
Gate array design is a manufacturing method in which diffused layers, each consisting transistors and other active devicesare predefined and electronics wafers containing such devices are "held in stock" or unconnected prior to the metallization stage of the fabrication process. The physical design process defines the interconnections of these layers for the final device.
For most ASIC manufacturers, this consists of between two to nine metal layers with each layer running perpendicular to the one below it.gate-level model High-Level Behavioral Register Transfer Level Gate Level Courtesy of Arvind L Writing synthesizable Verilog: Such a GCD description can be easily written in Behavioral Verilog It can be simulated but it will have nothing to do with.
A decoder is a multiplexer whose inputs are all constant with distinct one-hot (or one-cold) coded values. Please refer to the "Multiplexers" section of this chapter for more details.
|Microprocessor Report Archive||Supercomputer Scientific computing is a much smaller niche market in revenue and units shipped. It is used in government research labs and universities.|
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This section shows t wo examples of 1-of-8 decoders using One-Hot and One-Cold coded values. //Gate Level description of Half Adder module half_adder(x,y,s,c); input x,y; output s,c; xor(s,x,y); and(c,x,y); // instantiate a 3 to 8 decoder Dec #(3,8) d1(in,b) ; Writing a Test Bench Use initial and always to generate inputs for the unit you are testing.
Foreword (by Frank Vahid) > HDL (Hardware Description Language) based design has established itself as the modern approach to design of digital systems, with VHDL (VHSIC Hardware Description Language) and Verilog HDL being the two dominant HDLs. Microchip Debuts Dual-Core DSC New dsPIC33CH Challenges Bit Digital Signal Controllers.
Microchip's new dsPIC33CH is an unusually capable bit digital signal controller (DSC) that combines the functions of a microcontroller and DSP. An Application-Specific Integrated Circuit (ASIC / ˈ eɪ s ɪ k /) is an integrated circuit (IC) customized for a particular use, rather than intended for general-purpose use.
For example, a chip designed to run in a digital voice recorder or a high-efficiency Bitcoin miner is an ASIC.
Application-specific standard products (ASSPs) are intermediate between ASICs and industry standard.