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 the S-Parameter data is versus frequency.
See S-parameter detail in References > S-Parameter Channel Examples.
S-Parameter data inherently is used to represent SerDes system channels, transmit (Tx) or receive (Rx) integrated circuit (IC) input or output analog buffers, IC packaging, and more.
The S-Parameters for an N port device are typically represented with the symbol Sij, where i represents the port of interest with an output wave, and j represents the port with an incident input wave, with i and j being integers in the range 1 to N. Thus, S21 means port 2 contains the measured output wave and port 1 has the incident input wave.
Within the Compare S-Parameters Tool, the S-Parameters from two different files can be viewed and compared for their reflection characteristics (i=j), transmission characteristics (i>j), or reverse transmission characteristics (i<j). The characteristics are viewed with magnitude (dB) and phase (deg) versus frequency. Additionally, the passivity factor for the S-Parameters can be displayed versus frequency.
S-Parameters are considered passive if the following condition is met:
Sum(i=1, 2, …, N){ |Sij|^2 } <= 1 for each j=1, 2, …, N
This condition essentially means that the sum of the power out of an N port cannot be greater than the port into the N port.
To compare S-Parameters, use the web site: https://rfsystemsdesign.com/compare-sparameters-tool/
Do this by entering your data in the fields for 1. Define System and 2. Setup Analysis. Upload your S-Parameter file (SParamFileA) and identify the number of ports that it has. List a second file which was separately and previously uploaded (SParamFileB) and identify the number of ports it has (which should be the same as for SParamFileA). For each file A and B, identify which ports are to be considered the differential channel + and – input and output ports. Additionally, list the ports to be measured (up to 4 integer values) and whether phase is to be displayed unwrapped versus frequency or not.
To compare S-Parameters select Run in field 3. Run Analysis.
Within Field 4. Display Results, you can select to Open graphs for any of the reflection, transmission, and reverse-transmission S-Parameter paths. Additionally, you can observe the maximum passivity factor versus frequency.
For more detail on the data and graphs available from this web site, see the article: and Typical Compare SParameters Characteristics and Displays…