A Methodology for the Computation of an Upper Bound on Nose Current Spectrum of CMOS Switching Activity

Currents injected by CMOS digital circuit blocks into the powergrid and into the substrate of a system-on-a-chip may affect reliabilityand performance of other sensitive circuit blocks. To verify thecorrect operation of the system, an upper bound for the spectrum ofthe noise current has to be provided with respect to all possible transitionsof the circuit inputs. The number of input transitions is exponentialin the number of circuit inputs. In this paper, we present anovel approach for the computation of the upper bound that avoidsthe untractable exhaustive exploration of the entire space. Its computationalcomplexity is indeed linear in the number of gates. Ourapproach requires CMOS standard cell libraries to be characterizedfor injected noise current. In this paper, we also present an approachfor this characterization of CMOS standard cells. Experimental resultshave proven the accuracy of both the algorithm and the noisecurrent models used for the library characterization.