Model to hardware correlation for power distribution induced I/O noise in a functioning computer system

The Power Distribution System (PDS) for Input/Output (I/O) drivers in high-speed computer system is often separated from that for the microprocessor core. Modern computer systems contain hundreds of driver I/Os, decoupling capacitors and signal transmission lines that carry the data between chips. Simultaneous switching of these hundreds of drivers causes noise, i.e., voltage fluctuation on the power supply rail, which causes signal integrity problems of the data on the signal transmission lines. This paper discusses measurements of noise due to driver I/O switching in a high speed functioning computer system. The transfer impedance of a PDS was measured and noise of the functioning PDS in both frequency and time domain was measured. This paper presents an efficient methodology to model these noise waveforms. Modeling results have shown good agreement with measurements, demonstrating the application of the methodology to complex and realistic boards. Reduction of I/O switching noise through thin dielectric was also simulated using the modeling method presented.