Optimize the least required quantity of decoupling capacitors in PDN design

A least required quantity (LRQ) calculation of each decoupling capacitor (decap), considering power distribution network (PDN) lumped circuit model parameters is presented in this passage. The proposed method uses equivalent impedance which contains the impedance of Voltage Regulator Model (VRM) and the impedance of the Power/Ground Planes for the LRQ calculation. As to meet the PDN design requirements, the equivalent impedance combined with each capacitor’s impedance in parallel must not exceed the target impedance. Therefore, a more accurate LRQ calculation is presented. The results show that it can minimize the numbers of decoupling capacitors used in a PDN design and reduce the area occupied on board, compared with the conventional LRQ calculations. The simulations also demonstrate that the variation of the inductance between the VRM output and IC can affect the low frequency decap’s LRQ while the variation of plane capacitance can affect the high frequency decap’s LRQ. In general, the advantage of the proposed method is that it takes PDN circuit parameters into consideration which provides a new perspective of optimizing the numbers of decoupling capacitors in PDN design.