Eye Comparison Between Unencoded and 128b/130b-encoded NRZ Signals

Increasing requirement of data transfer between devices makes the communication standards raise the data rate. In PCI-SIG, the encoding scheme has changed from 8b/10b till Gen2 (till 5 Gbps) to 128b/130b encoding @ Gen3 and beyond (8 Gbps and beyond) to achieve the increasing demand for throughput. However, there is no discussion about the eye estimation of 128b/130b-encoded signals. This article discusses the estimation of statistical eye using 128b/130b encoding. It is shown that the encoded eye is similar to unencoded eye. A simple proof is proposed to explain the same. A few test cases are simulated for verifying the theory. In addition, the proposed eye estimation method is scalable to arbitrary encoding schemes.