The dominant substrate noise coupling mechanism is determined for multiple switching gates based on an intuitive model. The model exhibits reasonable accuracy as compared to SPICE. The regions where ground coupling and source/drain coupling dominate are described based on this model. The impact of multiple parameters such as the rise time, number of switching gates, decoupling capacitance, and parasitic inductance on the dominant noise coupling mechanism is investigated. The dominance of ground coupling in large scale circuits, as generally assumed, is shown to be invalid if sufficient decoupling capacitance is used or the circuit has a sufficiently low parasitic inductance such as a flip-chip package. The efficacy of several noise reduction techniques is discussed based on the application of the dominant noise analysis model.