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 concept of modularity enables the parallelisation of the design process. In the figure below magic satisfactorily joins one pair of diffusions while the other causes a design rule error: Your modu,arity with magic will not require explicit keep out masks, but you will be required to observe implied keep out areas as appropriate.

The following figure shows keep out areas for Metal1 and Metal2 for a part of a cell, together with internal elements sufficiently 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. Since no physical manufacturing step is necessary for customizing the FPGA chip, a functional sample can be obtained almost as soon as the design is mapped into a specific technology.

Design of VLSI Systems – Chapter 1

These modules are then geometrically placed onto the chip surface using CAD tools for automatic module placement followed by routing, with a goal of minimizing the interconnects area and signal delays. In fact magic can cope with diffusions closer than 1. The current leading-edge technologies such as low bit-rate video and cellular communications already provide the end-users a certain amount of processing power and portability.

Usually, other design concepts and design approaches are also needed to simplify the process. Gajski shown in Fig. Below are two abstract modulagity for NAND gates, illustrating some more complex features: Standard-cell based designs may consist of several such macro-blocks, each corresponding to a specific unit of the system architecture such as ALU, control logic, etc.


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. Note glsi all of these circuits were designed by using inverters and tri-state buffers only.

This approach is very similar to the software case where large programs are split into smaller and smaller sections until simple regularigy, with well-defined functions and interfaces, can be written. The designer attempts to divide the hierarchy into a set of similar blocks. The interconnection patterns to realize basic logic gates can be stored in a library, which can then regu,arity used to customize rows of uncommitted transistors according to the netlist.

Regardless of the actual size of the project, the basic principles of structured design will improve the prospects of success.

an The failure to properly verify a design in its early phases typically causes significant and expensive re-design at a later stage, which ultimately increases the time-to-market. The strategy is to avoid replacing a complex system design with a complexity of sub-modules.

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.

It also allows the use of generic modules in various designs – the well-defined functionality and signal interface allow plug-and-play design. The keep out area for each layer should extend for one half of one design rule distance beyond the edge of the cell. The adder can be decomposed progressively into one- bit adders, separate carry and sum circuits, and finally, into individual logic gates.

Also from the chip layout, circuit models which include interconnect parasitics can be extracted and used for timing simulation and analysis to identify timing critical paths. For instance, the inverter gate can have standard size transistors, double size transistors, and quadruple size transistors so that the chip designer can choose the proper size to achieve high circuit speed and layout density.


Although supported by magic, this style is not supported by Tanner L-Edit. Regularity can exist at all levels of abstraction: Regularity means that the hierarchical decomposition of a large system should result in not only simple, but also similar blocks, as much as possible. The current gate array chips can implement as many as hundreds of thousands of logic gates.

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. Cells may butt but should not overlap. For instance, if a chip designer defined an architecture without close estimation of the corresponding chip area, then it is very likely that the resulting chip layout exceeds the area limit of the available technology.

If necessary, the replication of some logic may solve this problem in large system architectures. Thus, it is very important to feed forward low-level information to higher levels bottom up as early as possible. 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.

Hierarchy Rules for Layout

To help you produce good hierarchical designs it is strongly suggested that you follow the conventions outlined below: A more detailed view showing the locations of switch matrices used for interconnect routing is given in Fig.

Here, the numbers for circuit complexity should be interpreted only as representative examples to show the order-of-magnitude.

The synthesized architecture is then technology-mapped or partitioned into circuits or logic cells.

Wiring should not normally overlap a sub-cell. Unfortunately it’s ability to cope depends on the alignment of the diffusions.