Signal 'ramp implicit quantity

Dear all,

As it's known that the s'ramp(trise,tfall) is quantity with the same type as
signal s. So this limit the signal s to be of floating-point type or
subtypes.

Is there is a way to change a bit signal to quantity using the same
attribute sbit'ramp directly? or the model writer should write the code for
conversion, by adding another real signal for instance and so on.....

Same for other types std_logic,....................

Thank you,

Amro Tork