Signoff (electronic design automation)

In the automated design of integrated circuits, signoff (also written as sign-off) checks is the collective name given to a series of verification steps that the design must pass before it can be taped out. This implies an iterative process involving incremental fixes across the board using one or more check types, and then retesting the design. There are two types of sign-off's: front-end sign-off and back-end sign-off. After back-end sign-off, the chip goes to fabrication. After listing out all the features in the specification, the verification engineer will write coverage for those features to identify bugs, and send back the RTL design to the designer. Bugs, or defects, can include issues like missing features (comparing the layout to the specification), errors in design (typo and functional errors), etc. When the coverage reaches a maximum% then the verification team will sign it off. By using a methodology like UVM, OVM, or VMM, the verification team develops a reusable environment. Nowadays, UVM is more popular than others. During the late 1960s engineers at semiconductor companies like Intel used rubylith for the production of semiconductor lithography photomasks. Manually drawn circuit draft schematics of the semiconductor devices made by engineers were transeferred manually onto D-sized vellum sheets by a skilled schematic designer to make a physical layout of the device on a photomask. The vellum would be later hand-checked and signed off by the original engineer; all edits to the schematics would also be noted, checked, and, again, signed off. Signoff checks have become more complex as VLSI designs approach 22nm and below process nodes, because of the increased impact of previously ignored (or more crudely approximated) second-order effects. There are several categories of signoff checks. Layout Versus Schematic (LVS) – Also known as schematic verification, this is used to verify that the placement and routing of the standard cells in the design has not altered the functionality of the constructed circuit.