Impact of Worst-Case Excitation for DDR interface Signal and Power Integrity Co-Simulation

For the purpose of evaluating the impact of excitation on double data rate (DDR) interface system transmission performance, a methodology for generating the worst-case excitation is proposed for signal integrity (SI) and power integrity (PI) co-simulation. The excitation is produced with the pseudo random bit sequence (PRBS) gated by a square wave of the resonant frequency of the system power distribution network (PDN). The PRBS can reflect non-ideal factors as crosstalk, reflection and loss in the signal line, and the resonant frequency of the PDN can guarantee the maximum simultaneous switching noise (SSN). A data transmission performance simulation environment of currently widely used low power double data rate SDRAM4 (LPDDR4) is constructed based on the advanced I/O buffer information specification Plus (IBIS Plus) model. Compared with the ordinary PRBS excitation, in terms of eye diagrams, the proposed worst-case excitation reduces the eye width and eye height by 4.7% and 19.9%, respectively. Further analysis also proved that 1/2 duty ratio of the gating wave can maximize the influence from the power noise. In conclusion, the proposed worst-case excitation and test environment provide an improved SI/PI co-simulation scenario for the examination of the robustness of DDR system data transmission performance.