Delay Insensitivity Does Not Mean Slope Insensitivity!

Asynchronous circuits are well known for their intrinsic robustness to process, voltage and temperature variations. Nevertheless, in some extreme cases, it appears that their robustness is not sufficient to guarantee a correct circuit behavior. This limitation, which is caused by an analog phenomenon, appears when the transition slopes in input of C-elements become very slow. This paper describes in details this phenomenon and studies the robustness of different C-element topologies. The simulations, which have been performed in 130, 65 and 45 nm CMOS technologies, show an overview of the C-element behavior in presence of these slow ramps. This gives a comprehensive understanding of the phenomenon and suggests an appropriate approach for choosing the well-suited C-element topology for everybody facing these difficulties.