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New Concepts in Electric

MOST CAD SYSTEMS use two methods to do circuit design: connectivity and geometry.

  • The connectivity approach is used by every Schematic design system: you place components and draw connecting wires. The components remain connected, even when they move.
  • The geometry approach is used by most Integrated Circuit layout systems: rectangles of "paint" are laid down on different layers to form the masks for chip fabrication.

ELECTRIC IS DIFFERENT because it uses connectivity for all design, even Integrated Circuit layout. This means that you place components (MOS transistors, contacts, etc.) and draw wires (metal-2, polysilicon, etc.) to connect them. The screen shows the true geometry, but it knows the connectivity too.

The advantages of connectivity-based IC layout are many:

  • No node extraction. Node extraction is not a separate, error-prone step. Instead, the connectivity is part of the layout description and is instantly available. This speeds up all network-oriented operations, including simulation, LVS, and electrical rules checkers.
  • No geometry errors. Complex components are no longer composed of unrelated pieces of geometry that can be moved independently. In paint systems, you can accidentally move the gate geometry away from a transistor, thus deleting the transistor. In Electric, the transistor is a single component, and cannot be accidentally destroyed.
  • More powerful editing. Browsing the circuit is more powerful because the editor can show the entire network whenever part of it is selected. Also, Electric combines the connectivity with a layout constraint system to give the editor powerful manipulation tools. These tools keep the design well-connected, even as the circuit is modified on different levels of hierarchy.
  • Tools are smarter when they can use connectivity information. For example, the Design Rule checker knows when the layout is connected and uses different spacing rules.
  • Simpler design process. When doing schematics and layout at the same time, the typical design iteration is to get the layout to be design-rule clean before comparing it to the schematics (LVS) because the extractor cannot run if the design rules are wrong. Then, when LVS problems are found, the layout must be fixed and made DRC clean again. Since Electric can extract connectivity for LVS without having perfect design rules, the first step is to get the layout and schematics to match. Then the design rules can be cleaned-up without fear of losing the LVS match.
  • Common user interface. One CAD system, with a single user interface, can be used to do both IC layout and schematics. Electric tightly integrates the process of drawing separate schematics and its LVS tool compares them.

The disadvantages of connectivity-based IC layout are also known:

  • It is different from all the rest and requires retraining. This is true, but many have converted and found it worthwhile.
  • Requires extra work on the user's part to enter the connectivity as well as the geometry. While this may be true in the initial phases of design, it is not true overall. This is because the use of connectivity, early in the design, helps the system to find problems later on. In addition, Electric has many power tools for automatically handling connectivity.
  • Design is not WYSIWYG (what-you-see-is-what-you-get) because objects that touch on the screen may or may not be truly connected. Electric has many tools to ensure that the connectivity has been properly constructed.