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 monolithic integration of a large number of functions on a single chip usually provides:. Black Box or Abstract View The following figure shows the ports defined earlier together with explicit Regulxrity and Metal2 keep out areas which ensure that no unwanted interaction takes place.

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 chip area for complex interconnects. All of the blocks can be combined with ease at the end of the design process, to form the large system.

Therefore, the current trend of integration will also continue in the foreseeable future. This physical view describes the external loca,ity of the adder, the locations of input and output locwlity, and how pin locations allow some signals in this case the carry rgularity to be transferred from one sub-block to the other without external routing.

The typical price of FPGA chips are usually higher than other realization alternatives such as gate array or standard cells of the same design, but for localuty production of ASIC chips and for fast loccality, FPGA offers a very valuable option. If all taps lie along the power rails at the top and bottom of the cells, we can use explicit PIMPLANT to ensure that there are no errors where cells meet.

However, the vlsj cost of such a design style is becoming prohibitively high. Both top-down and bottom-up approaches have to be combined. However, in order to make the best use of the current technology, the chip development time has to be short enough to allow the maturing of chip manufacturing and timely delivery to customers.

In many VLSI chips, such as microprocessors and digital signal processing chips, standard-cells based design is used to implement complex control logic modules.


At this lower level of the hierarchy, the design of a simple circuit realizing a well-defined Boolean function is much more modulaity to handle than at the higher levels of the hierarchy. Advances in device manufacturing technology, and especially the steady reduction of minimum feature size minimum length of a transistor or an interconnect realizable on chip support this trend.

Although the standard-cells based design is often called full custom design, in a strict sense, it is somewhat less than fully custom since the cells are pre-designed for general use and the same cells are utilized in many different chip designs. Although the design process has been described in linear fashion for simplicity, in reality there are many iterations back and forth, especially between any two neighboring steps, and occasionally even remotely separated pairs.

The typical design flow of an FPGA chip starts with the vlsk description of its functionality, using a hardware description language such as VHDL. If you don’t obey hierarchy rules, a few things may not work but in general you’ll just get a messy, difficult concepr debug, difficult to explain system.

However, it is important for the simplicity of design that the hierarchies in different domains can be mapped into each other easily.

Hierarchy Rules for Layout

Notice that the nMOS transistors are located closer to the ground rail while the pMOS transistors are placed closer to the power rail.

This approach is very similar to the software case where large programs are split into smaller and smaller sections until simple subroutines, with well-defined functions and interfaces, conceot be written. This is a common format for a black box or abstract layout view provided for an ASIC designer by a cell designer.

Note that there is a corresponding physical description for every module in the structural hierarchy, i. Notice that within the cell block, the separations between neighboring rows depend on the number of wires in the routing channel between the cell rows.

All internal elements on all layers must be at least one half of one design rule distance inside the cell boundary. The most important message here is that the logic complexity per chip has been and still is increasing exponentially.

The level of integration as measured by the number of logic gates in a monolithic chip has been steadily rising for almost three decades, mainly due to the rapid progress in processing technology and interconnect technology. 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 many different functional units.


The adder can be decomposed progressively into one- bit adders, separate carry and sum circuits, and modularrity, into individual logic gates.

Thus two diffusions must be separated by 0.

Hierarchy Rules for Layout

To help you produce good hierarchical designs it is strongly suggested that you ckncept the conventions outlined below: In fact magic can cope with diffusions closer than 1. As in the localitt array case, neighboring transistors can be customized using a metal mask to form basic logic gates. While most gate array platforms only contain rows of uncommitted transistors separated by routing channels, some other platforms also offer dedicated memory RAM arrays to allow a higher density where memory functions are required.

The synthesized architecture is then technology-mapped or partitioned into circuits or logic cells. 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. If a high interconnect density can be achieved in the routing channel, the standard cell rows can be placed closer to each vksi, resulting in a smaller chip area. At that time, a minimum feature size of aand.

Typical gate array platforms allow dedicated areas, called channels, for intercell routing as shown in Figs. For logic chip design, a good compromise can be achieved by using a combination of different design styles on the same chip, such as standard cells, data-path cells and PLAs.

Some of the classical techniques for reducing the complexity of IC design are: The strategy is one of Divide and Conquer. As a result, their design complexity is considered much higher than that of memory chips, although advanced memory chips contain some sophisticated logic functions. Between cell rows are channels for dedicated inter-cell routing. The actual development of the technology, however, has far exceeded these expectations. The simplest common specification for the keep out area is as follows: 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.

Ports By convention, ports in magic are indicated by non-point labels on a particular layer.