CST – Computer Simulation Technology

RJ45 Interconnect Signal Integrity

This work was performed by North East Systems Associates (NESA), a consulting firm with expertise in high performance engineering and design, http://www.nesa.com.

STEP files of the RJ45 male and female connectors were imported into CST MICROWAVE STUDIO® (CST MWS).  This connector has 4 differential pairs and, for each of the pairs, discrete ports were used.  Simulations are performed in the time domain, looking at time domain reflection and transmission.  Figures 1 and 2 show the male and female ports of the RJ45 connector.



Figure 1: RJ45 Plug discrete ports



Figure 2: RJ45 Jack discrete ports

A time domain simulation was performed in Microwave Studio, launching the time domain reflectometry (TDR) excitation at the plug end of the connector.  Figure 3 shows the TDR profile of the 4 connector pairs.  Port 3 (wires 3-6) has more inductance and a larger discontinuity than the other ports. The reason for this is that the wires in Port 3 are uncoupled within the connector, placed outside the Port 5 pins (see Figure 1)....

Figure 4 displays the measured TDR profile of this connector.



Figure 3: Simulated TDR waveforms



Figure 4: Measured TDR waveforms

Both the measurements and simulations show the difference between the Port 3 pair and the others.  There is good correlation between the CST MWS simulations and TDR measurements.

Further simulations were performed to investigate frequency domain behavior of the RJ 45 connector. Figures 5 and 6 show S-parameters of the connector pair.  Figure 5 is the Return Loss, (S11), and Figure 6 is the Insertion Loss (S21). 

Notice that Port 3 has worse behavior than the other 3 pairs, for the same reasons mentioned above.



Figure 5: RJ45 Connector Simulated Return Loss



Figure 6: RJ45 Connector Insertion Loss

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