Virtuoso AMS Environment User Guide

Designing for Virtuoso AMS Compliance

Using Cell Parameters

Be sure to follow these guidelines for cell parameters as you develop your design.

■Ensure that cell parameters are defined in the CDF and that they have defined default values.

If cell parameters are not defined in the CDF, the netlister looks in environment files for a specified value. If no value is found, the netlister uses 0 as the default value for integer type parameters and uses 0.0 as the default value for all other parameters, including string parameters.

■If you develop a Verilog® cellview outside of the AMS environment and then use the cellview within the environment, be sure that the default parameter values in the original Verilog view are the same as the default values for the same parameters in the cell CDF. Following this guideline ensures that the values in the original Verilog cellview are consistent with the values used in cellviews generated by the AMS environment.

Using Efficient Formats for Parameter Values

You can speed up netlisting by entering parameter values in the format that you want them to be used in the netlist. For example, if you want the value 5.46u to appear as 0.00000546 in the netlist, use the expanded form to define the parameter.

This guideline is especially pertinent for the VHDL-AMS netlist language, which does not support the use of scaling factors.

Parameterized Cells

In the AMS environment, follow this restriction on using parameterized cells.

In schematic and layout views, do not use parameterized cells that change internal connectivity. For example, do not use parameterized cells that change the number or width of terminals or instances. You can, however, use parameterized cells to vary shapes and sizes, such as the width or shape of a transistor.

Be sure that you define the parameters used in parameterized cells either in the cell CDF or as instance properties.