Designing power bus decoupling for CMOS devices

The adequacy of the DC power bus decoupling for CMOS devices can be determined if the effective board decoupling capacitance, the CMOS load capacitance, the CMOS power dissipation capacitance, the switching time, and the allowable bus noise voltage are known. A simple method is presented for estimating the effective decoupling capacitance. The load and power dissipation capacitance values are shown analytically and experimentally to be closely related to the transient current. The transient current and switching time are used to estimate the transient noise voltage on the power bus.