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Design Notes
CPW Layout Schematic
This example demonstrates CPW layout and the concept of negative layers for layout. For the CPW models, the default layout cells require 6 layers in the lpf file:
(Layername)
(Layername)+
(Layername)-
Thick Metal
Nitride Etch
Air Bridge
The first three layers can have any name as long as there is a "neutral", "-" and "+" layer. For example:
First Metal = center conductor
First Metal+ = ground
First Metal- = space
In this example the ground planes were drawn using both the First Metal+ and Pre Plate+ layers. The models use a line type of Inset line that uses the layers First Metal and Pre Plate for the center conductors and First Metal- and Pre Plate- for the space .
Thick Metal, Nitride Etch, and Air Bridge are used to draw the air bridge for bends, tees, and the CPWABRG models.
Compare CPW Lines Schematic
This schematic shows how the negative layers work. Look at the layout for this schematic:
1. Inset Line with layers First Metal+ and Pre Plate+: This shows how line types are used. The inset line type consists of layers First Metal and Pre Plate. The layout for this line type automatically draws the space for the model on the First Metal- and Pre Plate- layers. The ground planes are drawn with the Pre Plate+ and First Metal+ layers so that the spaces are subtracted properly.
2. First Metal line with First Metal+: This helps to illustrate further how the cells are automatically drawn. If there is only one layer in the line type the subtraction from the ground plane only happens with the corresponding negative layer. In this case, the negative layer First Metal- subtracts from First Metal+.
3. First Metal line with layers First Metal+ and Pre Plate+: This case shows both First Metal+ and Pre Plate+ drawn as ground planes. Notice the subtraction of the space for the Pre Plate layer does not occur. This is because the line type only consists of the First Metal layer. The draw code does not recognize the negative layer of the Pre Plate layer because the line type does not specify the layer.