antenna init [cellname]
antenna check
antenna fix
where cellname is the name of a known standard cell that implements an antenna tie-down (diode to n-well and/or substrate). The named cell must appear in the LEF file of standard cell macros passed to qrouter, and in the DEF input file.
The antenna command comes in three forms depending on the option. The init option should be run before the input DEF file is read, and indicates which cells in the DEF COMPONENTS block are to be used for antenna violation fixes. Qrouter does not modify the layout floorplan, and so to fix antenna violations, the design must contain some number of "free" antenna cells (those whose input pins are not already assigned to nets).The check option analyzes a routed design for antenna violations and reports what it finds in output to the terminal. This option is purely informational, as no attempt is made to fix the antenna violations.
The fix option performs antenna violation fixing by routing portions of nets that are in violation of antenna rules to the nearest available free antenna tie-down input. Depending on the "verbose" setting, it does not report on violations found. It will generate an error message if there are too few (or none, or unroutable) free antenna taps to use to correct the violations.
A quick background: Antenna issues are caused when, during fabrication, a polysilicon transistor gate is attached to a long piece of unterminated metal. If long enough, the metal acts as an antenna, collecting RF energy during processing and generating enough charge to punch through a transistor gate. Antennas can be terminated by attaching them to n- or p- diffusion, such as a diode or a transistor source or drain. Since all CMOS output stages are transistor drains, generally speaking all wires in a circuit are terminated in a completed chip. However, in the middle of processing, when only some of the metal layers have been fabricated, some wires may be incomplete and therefore form antennas. This implies that antenna checks must be done separately considering each step of processing the metal layers in a design.
Foundry rules provided in a technology LEF file usually declare what ratio of metal area to gate area is considered an antenna violation, and what method to use to calculate if a design violates the antenna rules. If no such information exists in the LEF file, then qrouter cannot perform any checks or fixes. Likewise, if there is no dedicated cell in the standard cell set for anchoring antenna wires, or no such cells are scattered throughout the layout, then checks can be made but fixes cannot be performed.
antenna is implemented as a built-in command in qrouter.
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Last updated: May 22, 2018 at 10:08pm