Effects of on-package decoupling capacitors on the simultaneous switching noise

Effects of on-package decoupling capacitors on the simultaneous switching noise (SSN) of output drivers are presented. The effectiveness of the capacitor is a function of inductance from switching drivers to capacitors, and the signal/VSS/VDD stack-up of the package. For a μ-strip structure, the decoupling capacitor provides an AC shunt path between VSS and VDD that minimizes the impedance for signal transmission that leads to the reduction of SSN. The reduction of SSN is dependent on the inductance from chip pad to decoupling capacitor. Increasing this inductance will render the capacitor ineffective. For a tri-layer stripline structure, the decoupling capacitor has little effect on SSN reduction. SSN simulation results are compared and are consistent with the measurement data of an SSN dynamic electric test chip