Accurate Timing and Noise Analysis of Combinational and Sequential Logic Cells Using Current Source Modeling

Abstract

A current source model (CSM) for CMOS logic cells is presented, which can be used for accurate noise and delay analysis in CMOS VLSI circuits. CS modeling is broadly considered as the method of choice for modern static timing and noise analysis tools. Unfortunately, the existing CSMs are only applicable to combinational logic cells. In addition to multistage logic nature of the sequential cells, the main difficulty in developing a CSM for these cells is the presence of feedback loops. This paper begins by presenting a highly accurate CSM for combinational logic cells, followed by models for common sequential cells, including latches and master slave flip-flops. The proposed model addresses these problems by characterizing the cell with suitable nonlinear CSs and capacitive components. Given the input and clock voltage waveforms of arbitrary shapes, our new model can accurately compute the output voltage waveform of the sequential cell. Experimental results demonstrate close-to-SPICE waveforms with three orders of magnitude speedup.