A SerDes channel typically is a differential signal transmission channel. A hardware SerDes channel is typically characterized by measuring its N-port S-parameters and is typically a 4-port. The 4-port differential input ports are typically port 1 (+) and port 3 (-). The associated differential output ports are typically port 2 (+) and port 4 (-). The differential characteristic ( Port 1 – Port 3 vs. Port 2 – Port 4) is the channel transmission characteristic and is observed versus frequency.
See S-parameter detail in References > S-Parameter Channel Examples.
The eye analysis is performed on the channel that was first analyzed using the Channel Analysis Tool.
The S-parameter file data used in the Channel Analysis Tool is automatically adjusted as needed to conform to the physical realizability constraints of passivity, reciprocity, and causality, as well as reduction of noise in the S-parameters. The ports of the S-parameter data are terminated in the characteristic resistance specified in the S-parameter files. Within the Channel Analysis Tool an optimal FFE is applied to open the channel eye performance.
Once the channel with optimal FFE equalization is analyzed, the Eye Analysis Tool provides detail channel eye analysis, including jitter and BER analysis, The Eye Analysis Tool uses the channel characteristics obtained using the Channel Analysis Tool.
Within Field 1. Define System, one can specify the transmit (Tx) and receive (Rx) jitter characteristics. The jitter characteristics can include random gaussian jitter (Tx_Rj, Rx_Rj), deterministic jitter (Tx_Dj, Rx_Dj), duty cycle distortion jitter (Tx_DCD, Rx_DCD), and periodic jitter (Tx_Sj, Tx_Sj_Frequency, Rx_Sj, Rx_Sj_Frequency). The jitter can be specified in time units or UI (unit bit time interval) units.
Within Field 2. Setup Analysis, one can specify the sampling time offset from eye center for BER measurements, the sampling voltage offset from 0 for BER measurements, three BER levels for eye BER contours, and time display (x-axis) unit option (in sec or UI units, or as offset from eye center in sec or UI units).
After the analysis is Run from Field 3, many graphical displays are available to Open from Field 4.
See Typical Eye Characteristics and Displays for more detail.