Modified Channel Quality Comparison for PCI Express* 4.0

The Channel Quality Comparison (CQC) method was introduced in 2011^[1]. It is commonly used in the pre-layout simulation to estimate the risk of the channel, for high speed SERDES (Serializer/Deserializer) and DDR interfaces. However, once the equalizer inside the transmitter (Tx) and the receiver (Rx) becomes more and more powerful, the eye height (EH) and the eye-width (EW) will have less difference in thee effective range. Since CQC is a comparative method which relies on comparing the EH and EW between the current channel and the reference one, this phenomenon will introduce uncertainty. Although using the “DOE/RSM” (Design of Experiment /Response Surface Methodology) method may overcome the issue, it simply requires more resource. Not all projects or channels have the luxury to conduct a comprehensive simulation. In this paper, a modified CQC method is proposed to find a balance between speed and the accuracy.