def id_vd(self,vgs=None,vds=None,rounding=True):
        """
        Calculates drain-source current from 
        terminal voltages and gm
        """
        <code>
        if state=='ON':
            if vds <= vgs - vth:
                ids = self._params_['gm']*(vgs - vth - (vds/2))*vds
            else:
                ids = (self._params_['gm']/2)*(vgs-vth)**2

        <more code...>