Method and apparatus to target pre-determined spatially varying voltage variation across the area of the VLSI power distribution system using frequency domain analysis

A method of estimating decaps required for an IC during an initial floorplanning design phase begins by obtaining voltage variation waveforms for a plurality of nodes in a power distribution network of the IC. Next, the method computes a minimum value for each of the voltage variation waveforms and selects voltage variation waveforms below a minimum threshold value. Following this, an FDA is performed on the voltage variation waveforms below the minimum threshold value to create a set of frequency values. This involves performing an FFT on each of the voltage variation waveforms to obtain frequency domain data, wherein frequencies that cause a drop in voltage in the plurality of nodes are filtered. The method then sorts the frequency domain data, wherein the frequency domain data is arranged in order based on amplitude value, total power, frequency components, and/or amplitude of imaginary components.