Abstract
The signal integrity of the circuit, as one of the important design issues in high-speed digital system, is usually seriously affected by the signal reflection due to impedance mismatch in the DDR3 bus. In this paper, a novel optimization method is proposed to optimize impedance mismatch and reduce the signal refection. Specifically, by applying the via parasitic, an equivalent model of DDR3 high-speed signal transmission, which bases on the match between the on-die-termination (ODT) value of DDR3 and the characteristic impedance of the transmission line, is established. Additionally, an improved particle swarm optimization algorithm with adaptive perturbation is presented to solve the impedance mismatch problem (IPSO-IMp) based on the above model. The algorithm dynamically judges particles' state and introduces perturbation strategy for local aggregation, from which the local optimum is avoided and the ability of optimization-searching is activated. IPSO-IMp achieves higher accuracy than the standard algorithm, and the speed increases nearly 33% as well. Finally, the simulation results verify that the solution obviously decreases the signal reflection, with the signal transmission quality increasing by 1.3 dB compared with the existing method.
Highlights
As the most popular memory, DDR3 illustrates faster speed, higher data rate, and lower operating voltages than DDR2, with the data rate up to 1.6 Gbps or even higher at the operating voltage of 1.5 V
During the high-speed signal transmission, sudden changes of transient impedance will lead to discontinuity of signal line impedance, which results in signal reflections and substantial overshoot, undershoot, and ringing
The conducted experiments concluded that the ODT and characteristic impedance of transmission line play an important role in reducing signal reflection
Summary
As the most popular memory, DDR3 illustrates faster speed, higher data rate, and lower operating voltages than DDR2, with the data rate up to 1.6 Gbps or even higher at the operating voltage of 1.5 V. Lin et al [3, 4] proposed an approach to optimize ODT and routing parameters using PSO, which obtains ideal results Such researches usually attach importance to the effects of transmission line itself on the signal but neglect discontinuity problems caused by the via. The strategy considers the impact of via on high-speed signal; (2) we propose an improved particle swarm optimization algorithm with adaptive perturbation, which optimizes routing length of DDR3 signal, characteristic impedance, via parasitic impedance, and the impact of ODT on high-frequency signal quality; (3) the experiments demonstrate that the strategy proposed could improve effectively impedance continuity of transmission line and reduce reflection effects of high-speed signals.
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