Fuse circuits and methods that can sense the state of a fuse that is programmed but not open

Abstract

Fuse circuits and methods program a fuse by applying a program current to the fuse that is sufficient to increase the impedance of the fuse without opening the fuse, apply a sensing current to the fuse in response to a reset signal and otherwise sense whether the fuse is programmed without applying sensing current to the fuse. By maintaining essentially zero current through the fuse after programming, reduced current consumption and accurate sensing of programming state can be maintained, even though programming the fuse does not produce an open circuit, but rather only increases the impedance of the fuse. More specifically, a sensing current is applied to the fuse, to thereby determine the programmed or unprogrammed state of the fuse, wherein the fuse has a low impedance in the unprogrammed state, and the fuse has a high impedance but is not open in the programmed state. The programmed or unprogrammed state of the fuse is latched. Application of the sensing current is then terminated. The sensing current may be applied in response to activation of a reset signal, and application of the sensing current may be terminated in response to deactivation of the reset signal.