What is LVS and Inputs required? Difference between schematic and layout views? Is it a functional check?

o   LVS (Layout Versus Schematic): A critical physical verification process that compares the electrical circuit extracted from the physical layout database (e.g., GDSII, OASIS) against the intended circuit described by the source schematic netlist (e.g., SPICE or Verilog netlist).

o   Inputs:

o   Layout Database: The physical layout design file (GDSII, OASIS)

o   Source Netlist: The "golden" netlist representing the intended circuit schematic (e.g., SPICE netlist for custom designs, Verilog netlist for digital designs).

o   Rule Deck: Provided by the foundry, this file tells the LVS tool how to identify devices (transistors, resistors, capacitors, diodes) from the layout layers, how to determine connectivity, and how to extract parameters (like W/L for transistors).

o   Configuration/Setup Files: Files to control the LVS run, specify top cells, map power/ground names, define device properties to compare, set tolerances, etc.

o   Schematic View vs. Layout View (in LVS context):

§  Schematic View: Circuit from Golden netlist.

§  Layout View: Refers to the circuit extracted by the LVS tool from the physical layout geometry, GDS/OASIS

§  LVS Comparison: The core LVS process compares the extracted layout netlist (components, parameters, connectivity) against the source schematic netlist.

o   Is it a Functional Check?

o   No, it doesn’t check functionality of design. LVS is primarily a structural check.

§  It verifies that the structure implemented in the layout (which devices exist, how they are connected, their parameters) matches the intended structure from the schematic.

§  It does not verify if the design performs the intended logical function (e.g., it won't tell you if your adder design actually adds correctly). Functional verification is done through simulation (RTL, gate-level) or formal verification (like LEC - Logic Equivalence Checking for digital designs).

§  However, LVS is crucial for ensuring functionality because errors it catches (like shorts, opens, wrong connections, wrong device sizes) would almost certainly cause functional failures.