Conventional physical design flow separates the design of power network and signal network. Such a separated approach results in slow design convergence for wire-limited deep sub-micron designs. In this paper, we present a novel design methodology that simultaneously considers global signal routing and power network design under integrity constraints. The key part to this approach is a simple yet accurate power net estimation formula that decides the minimum number of power nets needed to satisfy both power and signal integrity constraints prior to detailed layout. The proposed design methodology is a one-pass solution to the co-design of power and signal networks in the sense that no iteration between them is required in order to meet design closure. Experiment results using large industrial benchmarks show that compared to the state-of-the-art alternative design approach, the proposed method can reduce the power network area by 19.4% on average under the same signal and power integr...