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The !antenna Command: Check MOS Antenna Effect

Syntax: !antenna [layer_name layer_min_ratio]... [min_ratio]

In the design of CMOS circuits, design rules and guidelines often provide a limit on the area of a wire net connected to a MOS gate. During processing, the wire net can act as an ``antenna'' which accumulates charge, potentially damaging the thin MOS gate oxide. This command provides checking of antenna nets.

Note that this is part of the extraction system and not DRC. The DRC system presently does not maintain a sophisticated enough state to identify device contacts or follow wire nets.

The !antenna command utilizes the values of the technology file extraction keywords Antenna (in physical layer blocks) and AntennaTotal. These keywords provide values which are used as defaults, which can be overridden from the command line.

If given without arguments, the !antenna command will generate an argument list constructed from the defaults (if any). This is displayed in the prompt area, where it can be edited by the user. The run begins when the user presses the Enter key. If there are no defaults, or if an argument was given to the command, there is no prompt and the command runs immediately.

With no parameters given, the command will identify and print an entry for each wire net in the hierarchy of the current cell which connects to a MOS gate. The results go to a file, created in the current directory, named cellname.antenna.log, where cellname is the name of the current cell. The user is given a chance to view this file when the operation completes.

The parameters provide a ``filtering'' function, whereby only entries outside of the filter range are printed in the file. The filtering parameter is the ratio of wire net area to total gate area connected to the net. These ratios can apply to individual layers contained in the wire net, or the total wire net area. Only entries that exceed given parameters are printed in the log file.

For example,

!antenna POLY 20 M1 30 50

This will print wire nets where at least one of the following is true:

  1. The ratio of POLY area to gate area exceeds 20.
  2. The ratio of M1 area to gate area exceeds 30.
  3. The ratio of total wire net area to gate area exceeds 50.

Thus, the log file will typically contain only those nets that exceed the guidelines.

These ``bad'' nets can be displayed in the Select Path mode of the Path Selection Control panel. After the !antenna command has been run, and/or with the log file in the current directory, pressing the Load Antenna file button or the f key will prompt for an antenna net number. This is the number in the log file that begins the report for each net.

The file will be accessed, and the corresponding wire net will be extracted and highlighted. The wire net is identified via the reference bounding box provided in the log file, on the same line as the net number.

next up previous contents index
Next: The !netext Command: Batch Up: Extraction Previous: Extraction   Contents   Index
Stephen R. Whiteley 2022-05-28