This disclosure is to design a decoupling capacitor topology of IC’s in PCB layout to
effectively resolve EMI problem with minimum number of capacitors. The proposed
decoupling capacitor topology is to simulate the twisted wire principle which the
common mode ground noise is cancelled at ground when 2 current loops are in opposite
direction.
Determine the location of decoupling cap, we can control the current direction of the
IC’s since the decoupling cap would be the power source to the IC’s. By controlling the
current direction of 2 IC’s with opposite direction the common mode ground noise
would be cancelled at ground.
The proposed topology is to let decoupling capacitor located between the 2 IC’s. The
current flow for the 2 IC’s would start from the decoupling cap and end at the ground of
IC then back to the ground pin of cap. Current flow direction to first IC would start from
the right and the current flow direction to the other IC would start from the left. With
the opposite current direction, the magnetic flux of both of IC’s would have been
cancelled each other at ground
