NOTE :
1. The base level of Vix_DQS_FR/RF is VrefDQ that is DDR4 SDRAM internal setting value by Vref Training.
2. Vix_DQS_FR is defined by this equation : Vix_DQS_FR = |Min(f(t)) x Vix_DQS_Ratio|
3. Vix_DQS_RF is defined by this equation : Vix_DQS_RF = Max(f(t)) x Vix_DQS_Ratio