Anchor Reference

Anchors are virtual locations within a cell’s layout. They are exposed and can be referenced in placement and routing when defining specs (e.g. i3.Place). You can define custom anchors as well use pre-defined ones.

Custom anchors

Anchor

An anchor is a virtual element in a cell.

Defining custom anchors

On Layout, you can define anchors.

class MyPCell(i3.PCell):
    class Layout(i3.LayoutView):

        def generate(self, layout):
            layout += i3.Anchor(position=(0, 100), name="anchor1")
            layout += i3.Anchor(position=(200, 0), name="anchor2")
            return layout

Usage of custom anchors

When creating a circuit, you can use i3.place_and_route or i3.Circuit to easily refer to anchors of instances.

class MyCircuit(i3.PCell):
    class Layout(i3.LayoutView):

        def generate(self, layout):
            layout += i3.place_and_route(
                insts={
                    'mycell': MyPCell(),
                    'wg': i3.Waveguide(),
                },
                specs=[
                    i3.Place("mycell@anchor1", (100, 100)),
                    i3.Place('wg', (0, 0), relative_to='mycell@anchor2')
                ]
            )
            return layout

Usage of predefined anchors

There are also predefined anchors. Predefined anchors refer to cardinal points or lines defined on the instance’s bounding box. The predefined line-like anchors are C, N, E, S, W, defining horizontal or vertical lines passing through the center or the north, east, south and west edge of the bounding box respectively. The point-like ones are C, NE, CN, NW, CW, SW, CS, SE, CE. For example, C denotes the center point of the bounding box, NW denotes the top-left corner, and CS denotes the midpoint of the bottom edge. The code snippet below shows how to place the bottom-right corner of a waveguide at (-5, 10).

class MyCell(i3.PCell):
    class Layout(i3.LayoutView):
        def generate(self, layout):
            layout += i3.place_and_route(
                insts={"wg": i3.Waveguide()}, specs=[i3.Place("wg@SE", (-5, 10))]
            )
            return layout