CS/ECE 755: Discussion Session II
Agenda for today:
- Finish Automatic Layout (options)
- Begin Custom Layout
Cell Placement
IC Station Reference Manual: (run mgc_acroread)
(also chapter 4 of IC Station User Manual)
Floor-plan
Cell Placement
Initial:
Initial and Improve:
Random and Improve:
Resume:
Port Placement
Routing
Two methods:
- Over-the-Cell-Router (OCR)
- Channel Router
Routing Steps:
Routing Options:
- Initial and Improve Global Iterations:
Number of iterations for global routing. The
router minimizes the layout area by rerouting nets in congested areas.
- Feedthru Cost:
The OCR router can either insert an external feedthru between cells,
or an internal feedthru over the cell. A lower cost makes external feedthru more likely.
- Primary Routing Layer:
When it is based on the channel direction, Metal-2 is used
for vertical channels and Metal-1 for horizontal channels.
- Extra Tracks:
Number of extra track spaces to leave in each channel. This space
can be used for manual editing.
- Expand Channels:
Specify whether router is allowed to change size of channel areas.
Expert Routing Options:
- Channel Over Cell Routing:
Specify whether any routing space inside a cell should be used for channel routing.
- Capacity-Driven-Layout:
Specify whether the routing decisions should be based on minimizing
the capacitance of interconnections.
- Taper Power:
Specify whether the VDD/GND lines should be `tapered' during routing.
- Connect Block Power:
Specify whether VDD/GND connections should be made on all blocks.
- Create Power Grid:
Specify whether a grid of VDD/GDD lines should be created in all channels (when routing
blocks).
- Align Mode:
Specify alignment of layout blocks when routing is done.
Over-the-Cell-Routing (OCR) Options:
- Routing Levels:
The routing layers that will be used. The first layer specified is the least preferred.
- Operation Mode Type:
Specify whether routing should be done near the edges or the center of the channels.
- Restricted Levels:
It is possible to specify the Poly layer here, for initial route segments directly
from the gate of transistors.
- Work Factor:
Determines the number of iterations of the algorithm.
- Maximum number of Bends and Vias:
The bends refer to the same routing layer, while the vias refer to adjacent
routing layers.
Custom Layout
Tutorial 4 - custom layout of an inverter
Steps:
- Identify circuit!
- Printout design rules (from class web page)
- Obeying design rules, draw rectangles representing ALL
components/layers of the transistor
(ie. poly, wells, metal1, metal2...).
For example:
...and so on...
THE TRICK IS TO KEEP IN MIND THE GLOBAL PLAN WHILE OBEYING LOCAL RULES.
Read Adam Butts' "Layout Tips and Techniques" (off web page).