Circuits associated with fusible elements for establishing and detecting of the states of those elements

Abstract

A state detection circuit for a fusible element includes a differential sensing circuit that compares voltage at a detection point in a path containing the fusible element with that at a reference point in a path establishing a non-zero reference voltage. The paths are similarly configured except one contains the fusible element while the other contains a device establishing the reference voltage. The two paths in any given sensing circuit are located in close proximity to each other so that even though element parameters in the paths of different sensing circuits may vary significantly, those values track each other in the given sensing circuit. As a result, the normal non-zero value of the voltage at the reference point maintains a relationship to that at the detection point that enables the differential sensing circuit to detect between a fused and an unfused element irrespective of variation in circuit element parameters. In order to prevent detection circuits and other circuits on the chip being damaged, during blowing of the fusible elements, voltage level of the sensing circuits are chosen to isolate the detection circuits from the other circuits on the semiconductor chip and the excitation levels applied to the detection circuits are raised to maintain differential voltages in the detection circuits at sufficiently low levels to prevent damage.