High-level current macro model for logic blocks

The authors present a frequency domain current macro-modeling technique for capturing the dependence of the block current waveform on its input vectors. The macro model is based on estimating the discrete cosine transform (DCT) of the current waveform and then taking the inverse transform to estimate the time domain current waveform. The DCT of a current waveform is very regular and closely resembles the DCT of a triangular or a trapezoidal wave. The authors use this fact and the relation between the DCT, discrete Fourier transform (DFT), discrete time Fourier transform (DTFT), and the Fourier transform (FT) to infer the template functions for the current macro model. These template functions are characterized by using various parameters like amplitude, phase decay factor, time period, etc. These parameters are modeled as functions of the input vector pair using regression. Regression is done on a set of current waveforms generated for each circuit using HSPICE. These template functions are used in an automatic characterization process to generate current macro models for various CMOS combinational circuits.