The Layout Versus Schematic (LVS) is the class of

electronic design automation Electronic design automation (EDA), also referred to as electronic computer-aided design (ECAD), is a category of software tools for designing electronic systems such as integrated circuits and printed circuit boards. The tools work together ...

(EDA) verification software that determines whether a particular integrated circuit layout corresponds to the original schematic or circuit diagram of the design.

Background

A successful design rule check (DRC) ensures that the layout conforms to the rules designed/required for faultless fabrication. However, it does not guarantee if it really represents the circuit you desire to fabricate. This is where an LVS check is used. The need for such programs was recognized relatively early in the history of ICs, and programs to perform this comparison were written as early as 1975. These early programs operated mainly on the level of

graph isomorphism In graph theory, an isomorphism of graphs ''G'' and ''H'' is a bijection between the vertex sets of ''G'' and ''H'' : f \colon V(G) \to V(H) such that any two vertices ''u'' and ''v'' of ''G'' are adjacent in ''G'' if and only if f(u) and f(v) ...

, checking whether the schematic and layout were indeed identical. With the advent of digital logic, this was too restrictive, since exactly the same function can be implemented in many different (and non-isomorphic) ways. Therefore, LVS has been augmented by formal equivalence checking, which checks whether two circuits perform exactly the same function without demanding isomorphism.Fabio Somenzi and Andreas Kuehlmann, ''Equivalence Checking'', chapter 4 (volume 2) of ''Electronic Design Automation For Integrated Circuits Handbook'', by Lavagno, Martin, and Scheffer,

Check

LVS checking software recognizes the drawn shapes of the layout that represent the electrical components of the circuit, as well as the connections between them. This

netlist In electronic design, a netlist is a description of the connectivity of an electronic circuit. In its simplest form, a netlist consists of a list of the electronic components in a circuit and a list of the nodes they are connected to. A netwo ...

is compared by the "LVS" software against a similar schematic or circuit diagram's

. LVS checking involves following three steps: # Extraction: The software program takes a database file containing all the layers drawn to represent the circuit during layout. It then runs the database through many area based logic operations to determine the semiconductor components represented in the drawing by their layers of construction. Area based logical operations use polygon areas as inputs and generate output polygon areas from these operations. These operations are used to define the device recognition layers, the terminals of these devices, the wiring conductors and via structures, and the locations of pins (also known as hierarchical connection points). The layers that form devices can have various measurements performed to and these measurements can be attached to these devices. Layers that represent "good" wiring (conductors) are usually made of and called metals. Vertical connections between these layers are often called vias. # Reduction: During reduction the software combines the extracted components into series and parallel combinations if possible and generates a

representation of the layout database. A similar reduction is performed on the "source" Schematic netlist. # Comparison: The extracted layout netlist is then compared to the netlist taken from the circuit schematic. If the two netlists match, then the circuit passes the LVS check. At this point it is said to be "LVS clean." (Mathematically, the layout and schematic netlists are compared by performing a

Graph isomorphism In graph theory, an isomorphism of graphs ''G'' and ''H'' is a bijection between the vertex sets of ''G'' and ''H'' : f \colon V(G) \to V(H) such that any two vertices ''u'' and ''v'' of ''G'' are adjacent in ''G'' if and only if f(u) and f(v) ...

check to see if they are equivalent.) In most cases the layout will not pass LVS the first time requiring the layout engineer to examine the LVS software's reports and make changes to the layout. Typical errors encountered during LVS include: # Shorts: Two or more wires that should not be connected have been and must be separated. # Opens: Wires or components that should be connected are left dangling or only partially connected. These must be connected properly to fix this. # Component Mismatches: Components of an incorrect type have been used (e.g. a low Vt MOS device instead of a standard Vt MOS device) # Missing Components: An expected component has been left out of the layout. # Parameter Mismatch: Components in the

can contain properties. The LVS tool can be configured to compare these properties to a desired tolerance. If this tolerance is not met, then the LVS run is deemed to have a Property Error. A parameter that is checked may not be an exact match, but may still pass if the lvs tool tolerance allows it. (example: if a resistor in a schematic had resistance=1000 (ohms) and the extracted netlist had the a matched resistor with resistance=997(ohms) and the tolerance was set to 2%, then this device parameter would pass as 997 is within 2% of 1000 ( 997 is 99.7% of 1000 which is within the 98% to 102% range of the acceptable +-2% tolerance error) )

Software

Commercial software

* ''Assura'', ''Dracula'' and ''PVS'' by

Cadence Design Systems Cadence Design Systems, Inc. (stylized as cādence), headquartered in San Jose, California, is an American multinational computational software company, founded in 1988 by the merger of SDA Systems and ECAD, Inc. The company produces software, ...

* ''Calibre'' by

Mentor Graphics Siemens EDA is a US-based electronic design automation (EDA) multinational corporation for electrical engineering and electronics, headquartered in Wilsonville, Oregon. Founded in 1981 as Mentor Graphics, the company was acquired by Siemens ...

* ''Guardian LVS'' by Silvaco * ''Quartz LVS'' by

Magma Design Automation Magma headquarters at Santa Clara Magma Design Automation was a software company in the electronic design automation (EDA) industry. The company was founded in 1997 and maintained headquarters in San Jose, California, with facilities througho ...

* ''IC Validator'' by

Synopsys Synopsys is an American electronic design automation (EDA) company that focuses on silicon design and verification, silicon intellectual property and software security and quality. Products include tools for logic synthesis and physical desig ...

* ''PowerLVS'' -now SmartLVS by Silvaco * ''SmartLVS'' b
Silvaco
* ''VERI'' and ''HVERI'' b

Free software

* ''KLayout'' https://klayout.de/ * ''Netgen'' http://opencircuitdesign.com/netgen/

References

{{reflist Electronic circuit verification