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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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Hierarchy Rules for Layout

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

The third evolution starts with a behavioral module description. Other than this 0. Remember that diffusion spacing rules are likely to be greater than metal spacing rules. This design style provides a means for fast prototyping and also for cost-effective chip design, especially for low-volume applications.

Hierarchy, regularity, modularity and locality. If a high interconnect density can be achieved in the routing channel, the standard cell rows can be placed closer to each other, resulting in a smaller chip area.

A good example of regularity is the localiyt of array structures consisting of identical cells – such as a parallel multiplication array.

Hierarchy Rules for Layout

Here, one can identify four different design styles on one chip: At this lower level of the hierarchy, the design of a simple circuit realizing a well-defined Boolean function is much more easier to handle than at the higher levels of the hierarchy. Many advanced CAD tools for place-and-route have been developed and used to achieve such goals. Note that all of these circuits were designed by using inverters and tri-state buffers only. In fact magic can cope with diffusions closer than 1.


In the figure below magic satisfactorily joins one pair of diffusions while the other causes a design rule error: Below are two abstract layouts for NAND gates, illustrating some more complex features: The basic platform of a SOG chip is shown in Fig. A gap in the Metal2 keep out between B and Y indicates that the cell may be over-routed with Metal2 along this path.

Although supported by magic, this style flsi not supported by Tanner L-Edit. For timing critical paths, proper gate sizing is often practiced to meet the timing requirements. 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.

As an example of structural hierarchy, Fig. This trend is expected to continue, with very important implications localjty VLSI and systems design.

For intercell routing, however, some of the uncommitted transistors must be sacrificed. A good rule to use is to ensure that taps must be 1. Note here that the second row of cells is upside down so that the GND rails match. However, in order to make the best use of the current technology, locallity chip development time has to be short enough to allow iin maturing of chip manufacturing and timely delivery to customers.

Correspondingly, a hierarchy structure can be described in each domain separately. Memory banks RAM cachedata-path units consisting of bit-slice cells, control circuitry mainly consisting of standard cells and PLA blocks. Internal elements within the cell should be at least one half of one design rule distance inside the cell boundary.


A module is divided into sub-modules which in turn are sub-divided until the complexity of the modules becomes manageable. Regardless of the actual size of the project, the basic principles of structured design will improve the prospects of success.

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. In most cases, full utilization of the Rebularity chip area is not possible – many cell sites may remain unused. Regularity usually reduces the number of different modules that need to be designed and verified, at all levels of abstraction. A logic block can contain anywhere from 10 to transistors, depending on the function.

Since the same layout design is replicated, there would not be any alternative to high density memory chip design.

Unfortunately it’s ability to cope depends on anc alignment of the diffusions. The availability of dedicated memory blocks also reduces the area, since the realization of memory elements using standard cells would occupy a larger area.

The last evolution involves a detailed Boolean description of leaf cells followed by a transistor level implementation of leaf cells and mask generation. The actual development of the technology, however, has far exceeded these expectations.