This paper presents a methodology to analyze signal integrity such as power voltage drop and clock skew in early stages of design, more specifically, when RTL-design and early floorplanning are performed. In this stage, logic contents are not known, but global structure of power/ground and clock networks, function partitioning and early floorplan give reasonable accuracy for global optimization of the chip. A case study shows the power voltage drop and critical path delay slowdown due to dynamic power voltage drop for a mixed analog-digital chip, and a good match with actual measurements is achieved.