Transistor Placement with the Multi Row Stick Diagram
Introduction
The Stick Diagram is used to display transistors in a higher level abstract view for easier transistor manipulation. User's constraints are honored while transistors are moved, swapped, merged, aligned, split and folded. It is invoked when one or more transistors are selected and created from within the Design Browser, when instances are dragged and dropped from the Schematic window to the Layout window, or when a transistor is selected and the Selected Transistor to Stick Diagram toolbar icon in the Layout window is clicked. Multi row placement is an option available to users to further assist with transistor manipulation.
Cell Template
The transistor placement settings may be changed by using the Cell Template. It contains key parameters for the cell layout, including the P/N height, spacing, and alignment, power layer and rail definitions, and gate folding criteria. Further manipulation of the placement results like aligning, moving, splitting, merging and folding, may be done from within the Stick Diagram. The setting to enable multi row placement is accessed from the Cell Template.
To invoke the Cell Template, select Options-> Cell Template from the Layout window menu bar.
Figure 1: Cell Template Form
Stick Diagram
There are two operation modes for the Stick Diagram: Symbol, and Real Size. Symbol mode shows the transistor placement with just the symbol information. Real Size mode provides a better initial placement as it eliminates the discrepancy among placement, preview and realization by displaying a more accurate view of the transistors.
The 2 figures below show examples of Stick Diagram Mode set to Symbol and Real Size. Note the differences in the Stick Diagram with the different settings.
Figure 2a: Symbol Stick Diagram
Figure 2b: Real Size Stick Diagram
Enabling Multi Row Placement
To enable multi row placement and the Multi Row Stick Diagram, there are 2 settings required.
1. The Stick Diagram Mode needs to be toggled to Real Size on the Cell Template form.
Figure 3: Symbol Mode & Real Size Mode
When the Stick Diagram Mode is toggled to Real Size, the "Real Size" section in the Placement tab is enabled as shown in the Figures 4a and 4b.
Figure 4a: Real Size section disabled
Figure 4b: Real Size section enabled
2. Next, the Row Number needs to be set to a number greater than 1.
Figure 5: Multi row placement
This enables multi row placement and placement pattern selection.
Placement Patterns
There are 5 pattern placement options as shown in Figure 6.
Figure 6: Placement Pattern Selections
These patterns are:
Horizontal Right,
U-Shape (Clockwise),
U-Shape (Counterclockwise),
Circle (Clockwise) and
Circle (Countercolckwise).
The default placement pattern is Horizontal Right. When Row Number is set to 1, the placement pattern will be Horizontal Right. The 4 additional placement patterns are available only with multi row placement, when Real Size is selected and Row Number is greater than 1.
The following 5 figures are examples of the 5 placement patterns. The first one, Figure 7, shows the default placement, or Horizontal Right. The same circuitry is used in all 5. Look closely and notice the placement pattern that each one is using. The starting point for the placement is decided by the placement pattern.
Figure 7: Horizontal Right
Figure 8: U-Shape Clockwise
Figure 9: U-Shape Counter-Clockwise
Figure 10: Circle Clockwise
Figure 11: Circle Counter-Clockwise
Summary
The Stick Diagram may be configured to a user's preferences by modifying the settings in the Cell Template for that cell view. Different templates may be created for all cells. The Cell Template contains a set of transistor and realization constraints. Multi row transistor placement may be accomplished by modifying the Stick Diagram Mode and Row Number settings appropriately. For more information on all of these constraints, please see the Cell Template section in the Layout Window:Options Commands chapter of the Laker Command Reference Guide.
