Signal sensitivity to supply noise on high-speed I/O

Power Distribution Network (PDN) is optimized based on conventional AC and DC noise target specification. Large supply noise occurs due to increase in speed and number of I/O running simultaneously. In this paper, an alternate means to quantify supply noise to signal performance is discussed. Discussion focuses on signal performance impact caused by supply noise with different frequency content. Simulation is carried out using transistor model and findings are then correlated through lab measurements. Using USB I/O as a test case, findings conclude that the USB transmitter performance is less sensitive to supply noise at circuit operating frequency (480 MHz) and its harmonic. Hence, excessive AC noise at its less sensitive region will not cause signal eye diagram to fail.