Difference between revisions of "Ultrasim and Spectre"

Revision as of 07:32, 13 November 2009

For analog circuits described in Verilog - A include the following command into the file that runs Ultrasim, preferably toward the end: ahdl_include "<filename>"

To instantiate the models in the netlist, you can simply refer to it via a call to its module name.

Example:

Verilog-A module: inverter.va

`include "constants.vams"
`include "disciplines.vams"
module inverter(in, out);
     input in;
     output out;
     electrical in, out;
     parameter real high = 1.0
     parameter real low = 0.0;
     parameter real margin = 0.5;
     analog begin
          if (in < noise margin)
          out = high;
     else
          out = low;
     end
endmodule

Instantiating the module in the netlist file :

...
...
...
I0 (input, output) inverter
... 
ahdl_include inverter.va

The inverter module can be used as a subckt in spectre. Parameters defined in the Verilog-A module can also be changed during instantiation such as by:

I0 (input, output) inverter high=2.0 low=1.0 margin=1.5

Sample Buffer.ckt in Spectre
Sample Buffer.ckt in UltraSim

Running the Simulation

Both simulators can be accessed through the Analog Design Environment GUI or via Command line.

-Ultrasim Command Line (Start in lang=spectre mode)
ultrasim  -spectre -raw ./log_dir +log ./log_dir/ultrasim.out input.ckt

-Spectre Command Line
spectre  -raw ./log_dir +log ./log_dir/spectre.out input.ckt