Using Xic

Xic has two basic operating modes: physical and electrical. In physical mode, one is editing the geometry of the mask patterns on the multiple layers used in the photomasks to manufacture the circuit. In electrical mode, one is editing an electrical schematic of the circuit or subcircuit represented by the cell. The schematic is used for documentation, and also for performing simulation of the circuit to verify performance. The schematic and layout can be interlinked to provide consistency verification. This is the purpose of the functions in the Extract Menu, to be described in Chapter 16.

A full design database typically consists of a hierarchy of cells. The top level or main cell usually depicts the entire chip. Subcells represent the bond pads, annotation, and major circuit blocks. The circuit blocks in turn have subcells representing more primitive circuit blocks, down to the gate level and below.

In Xic, one can edit any of these cells and their subcells at any depth in the hierarchy, as both physical layout and electrical schematic. The use of a hierarchical database is far more efficient and convenient than a flat database. The designer is encouraged to make liberal use of subcells rather than designing single, highly complex cells.

When a design is complete, i.e., when all electrical simulations and physical design rule checks have been performed, the physical part of the database can be submitted for processing. The exact mechanism varies with organization, but the physical-only (Strip For Export button in the Export Control panel from the Convert Menu active) GDSII, OASIS and CIF outputs provided by Xic are portable to any mask fabrication facility or foundry.

The user can switch between physical and electrical modes at any time, by pressing the Electrical or Physical button (whichever appears) in the View Menu. Sub-windows, brought up with the Viewport button in the View Menu, are individually switchable between schematic and physical views. The side menus differ somewhat between the two modes, and some menu commands operate a little differently.

The next two sections of this chapter provide an introduction to editing in physical and electrical modes. The remaining sections provide information on certain Xic operation modes and features, and are somewhat more advanced in nature. The following chapters provide detailed information on all of the menu command functions.

The new user should read the first two sections of this chapter, and practice using Xic while reading the help messages.