issue in vhdl-ams compilation

Hi,

I'm trying to write a code for a comparator in vhdl-ams. I use incisiv (13.10.013) and when I compile the code (just the entity) an error is occuring:

This is my code:

library ieee;
use ieee.electrical_systems.all;
use ieee.std_logic_1164.all;
use ieee.math_real.all;

entity comparator is

 generic (level : real := 2.5; -- threshold
   vcc   : real := 5.0;   
   gnd   : real := 0.0);  

 port(--terminal e: electrical;  -- analogic in
            signal   s: out std_logic); -- digital out

end comparator;

When I write exactly what is below, the following error is occuring:

ncvhdl -work st_lib -message ../sources/comparateur_ent.vhdl
ncvhdl: 12.20-p001: (c) Copyright 1995-2012 Cadence Design Systems, Inc.
../sources/comparateur_ent.vhdl:
use ieee.electrical_systems.all;
        |
ncvhdl_p: *E,SELLIB (../sources/comparateur_ent.vhdl,2|8): unit (ELECTRICAL_SYSTEMS) not found in library (IEEE).
        errors: 1, warnings: 0

It look like that the library electrical_systems is not recognized by the compiler.

 Someone can help please?