The concept of modularity enables parallelization of the design process. Locality: The concept of locality in system ensures that the internal details of each Answer: VLSI Design flow consists of several steps which are carried out in linear . VLSI Design Methodologies EEB (Winter ): Lecture # 4Mani of Structured Design Techniques Hierarchy Regularity Modularity Locality; . architecture structure of accumulator is component reg — definition of. Digital VLSI Circuits. 1. Introduction to ASIC Design a. Design Strategies: Hierarchy, Regularity, Modularity & Locality b. Chip Design Options: Gate Array, Field.

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The last evolution involves a detailed Boolean description of leaf cells followed by a transistor level implementation of leaf cells and mask generation. Hierarchy, regularity, modularity and locality. Since the patterning of metallic interconnects is done at the end of the chip fabrication, the turn-around time can be still short, a few days to a few weeks.

Therefore, the current trend of integration will also continue in the foreseeable future. Memory circuits are highly regular and thus more cells can be integrated with much less area for interconnects.

In a fuller custom design, the entire mask design is done anew without use of any library. Generally speaking, logic chips such as microprocessor chips and digital signal processing DSP chips contain not only large arrays of memory SRAM cells, but also localitty different functional units. Black Box or Abstract View The following figure shows the ports defined earlier together with explicit Metal1 and Metal2 keep out areas which ensure that no unwanted interaction modulariyt place.

Each design style has its own merits and shortcomings, and thus a proper choice has to be made by designers in order to provide the functionality at low cost.

The power and ground rails typically run parallel to the upper and lower boundaries of the cell, thus, neighboring cells share a common power and ground bus. The typical design flow of an FPGA chip starts with the behavioral description of its functionality, using a hardware description language such as VHDL. Fully fabricated FPGA chips containing thousands of logic gates or even more, with programmable interconnects, are available to users for their custom hardware programming to realize desired functionality.


Regularity means that the hierarchical decomposition of a large system should result in not only simple, but also similar blocks, as much as possible.

Note that there is a corresponding physical description for every module in the structural hierarchy, i. As in the case of Sea-of-Gates, with over-the- cell routing, the channel areas can be reduced or even removed provided that the cell rows offer sufficient routing space. The concept of locality also ensures that connections are mostly between neighboring modules, avoiding long-distance connections as much as possible.

With the use of multiple interconnect layers, the routing can be achieved over the active cell areas; thus, the routing channels can be removed as in Sea-of-Gates SOG chips.

Magic will not enforce hierarchy rules.

Hierarchy Rules for Layout

Wiring should not normally overlap a sub-cell. Sophisticated computer-aided design CAD tools and methodologies are developed and applied in order to manage the rapidly increasing design complexity.

While most gate array platforms only contain rows of uncommitted transistors movularity by routing channels, some other platforms also offer dedicated memory RAM arrays to allow a higher density where memory functions are required.

There is no Metal2 keep out indicating that we can route Metal2 anywhere over the cell. Typically, the required computational power or, in other words, the intelligence of these applications is the driving force for the fast development of this field. The adder can be decomposed progressively into one- bit adders, separate carry and sum circuits, and finally, into individual logic gates. The interconnection patterns to realize basic logic gates can be stored in a library, which can then be used to customize rows of uncommitted transistors according to the netlist.

More sophisticated CLBs have also been introduced to map complex omdularity.

Hierarchy Rules for Layout

Other than this 0. It can be observed that in terms of transistor count, logic chips contain significantly fewer transistors in any given year mainly due to large consumption of regularitt area for complex interconnects.


If such improvement is either not possible or too costly, then the revision of requirements and its impact analysis must be considered. Note that all of these circuits were designed by using inverters and tri-state buffers only.

Several design styles can be considered for chip implementation of specified modularigy or logic functions. The strategy is one of Divide and Conquer. In the following, we will examine design methodologies and structured approaches which have been developed over the years to deal with both complex hardware and software projects.

The Y-chart first introduced by D. For this reason it is best to avoid this style in order to provide cells which are portable between different layout tools.

A gap in the Metal2 keep out between B and Y indicates that the cell may be over-routed with Metal2 regklarity this path. As in the gate array case, neighboring transistors can be customized using a metal mask to form basic logic gates. The keep out area for each layer should extend for one half of one design rule distance beyond the edge of the cell. The hierarchical aand approach reduces the design complexity by dividing the large system into several sub-modules.

Design of VLSI Systems – Chapter 1

A minimum size of 0. Where three metal layers are not in use, the following guidelines should be followed: The programming of the chip remains valid as long as the chip is powered-on, or until new programming is done. Below are two abstract layouts for NAND gates, illustrating some more complex features: At the logic level, identical gate structures can be used, etc.

The first phase, which is based on generic standard masks, results in an array of uncommitted transistors on each GA chip.

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