What is the difference between std. cell LEF and tech LEF? What content is in tech LEF?

o   Technology LEF (tech.lef): Defines the process technology rules and properties. It contains information common to the entire chip manufacturing process, independent of specific standard cells.

o    Content:

§  Layers: Defines all routing (metal), cut (via), masterslice (poly, diffusion), and other layers used in the technology. Includes name, type, direction preference, pitch, width, spacing rules (DRCs), resistance, capacitance per unit area/length, thickness, color (for multi-patterning).

§  Vias: Defines standard via types connecting different layers, including their cut patterns, enclosure rules, and resistance.

§  Sites: Defines the basic placement grid unit (SITE) for standard cells (e.g., core site), specifying its dimensions and symmetry.

§  Units: Defines database units (e.g., microns) and units for capacitance, resistance, time.

§  Manufacturing Grid: The minimum grid resolution for layout features.

§  Antenna Rules: Defines antenna ratios/rules for different layers.

§  Design Rules: Other general rules like minimum enclosed area, clearance measures.

§  Property Definitions: Defines custom properties that can be used later.

o   Standard Cell LEF (cells.lef or library specific LEF): Describes the physical abstract view of each individual standard cell (or macro) in the library.

o    Content:

§  MACRO Definition: Each cell is defined as a MACRO.

§  CLASS: Type of cell (e.g., CORE, PAD, BLOCK).

§  SIZE: Width and height of the cell, usually aligned to the SITE definition from the tech LEF.

§  SYMMETRY: Allowed orientations (e.g., X, Y, R90).

§  ORIGIN: Reference point within the cell.

§  PIN Definitions: For each logical pin (A, B, Y, CK, D, VDD, VSS, etc.):

§  Name

§  Direction (INPUT, OUTPUT, INOUT)

§  Use (SIGNAL, CLOCK, POWER, GROUND)

§  Shape (RECT for rectangle) and Layer (e.g., M1, M2) defining the pin's physical location and size.

§  PORT containing the geometric shapes.

§  OBS (Obstructions): Defines areas within the cell where routing is blocked on certain layers (e.g., routing blockages over the cell).

o    Relationship: The cell LEF relies on the definitions (layers, sites) established in the tech LEF. PnR tools read both to understand the process rules and the physical dimensions/pin locations of the cells they need to place and route.