This file controls how LEdit extracts a circuit from layout to a netlist, such as spice or ntk format. It includes instructions on which layers can be considered connected electrically, (i.e. Metal1 to Metal2 over a Via) and how arrangements of layers should be grouped into elements.

Associated Environment Variables

The "home directory" where LEdit starts in the directory tree to look for this file


This is a text file. The first part consists of directions on which layers LEdit should consider connected. The syntax is as follows:
	connect(layer1, layer2, actionlayer)
. . . which tells LEdit to connect layer1 to layer2 in the netlist if they overlap each other and both overlap the actionlayer. Note that layer1 or layer2 can be identical to the actionlayer, in which case everytime layer1 and layer2 overlapped, they would be connected.

The second part covers how elements are recognized and extracted. The syntax is as follows:

# The BogusMOS structure
device = SUBCKT(
               RLAYER = BogusMOSgate;
               Drain =  native diffusion, WIDTH;
               Sink =   poly not resistor;
               Stopper = native diffusion, WIDTH;
               Bulk =   all bulks;
               MODEL =  bogusmos;
In our 'BogusMOS' example, the first thing we notice is the comment with a pound sign at the start helping anyone reading this .ext file.

Next, is the 'device' directive. We define this device as a 'SUBCKT' or sub-circuit, a very general way to describe a circuit element in in spice terminology. A SUBCKT in a spice file can be composed of other spice elements, or be an element itself with no more primitive contents.


It is useful to include comments giving detailed information about the makeup of the derived layers that this file will expect to be present. The derived layers are taken care of in the setup.tdb, and it is always possible that something will happen to this file.


Here is neumos.ext that I use, a result of a long evolution in Carverland.