a circuit is provided to isolate a contact pad from a logic circuit of a die once the contact pad is no longer needed . this circuit can take many forms including a cmos multiplexer controlled by a fuse or anti - fuse , an nmos or pmos pass gate controlled by a fuse or anti - fuse , or even a fusible link which is severed to effect isolation . additionally , a circuit is provided that switchably isolates one of two contact pads from a logic circuit .