Evaluate Crosstalk-to-Signal Ratio

If transmission lines are placed in a homogeneous medium, crosstalk at the far end of the line will tend toward zero. Let's verify this scenario with a calculation in SimPCB Lite.

In this tutorial, we'll evaluate the crosstalk-to-signal ratio for a matched stripline transmission line. This line is located on the third layer of a sample 6-layer PCB stackup (see the image below) with a thickness of 1.5 mm. The characteristic impedance, source impedance, and load impedance are all 40 Ohm.

1. First, determine the trace width required to achieve a characteristic impedance of 40 Ohm for an Offset stripline (OS-1B1A) structure using the Lossless calculation type, as demonstrated in the Calculate Trace Width tutorial.

   

   The calculated trace width is 0.241 mm.

2. In the Calculation settings panel, switch calculation mode to Time domain and set the Parameters option to Crosstalk. The previously entered transmission line parameters will retain their values.

   

3. In the Advanced settings panel, set the following calculation parameters:

   • Set V1, Voltage (Port 1) to Signal
   • Set V3, Voltage (Port 3) to 0 V
   • Set LTL, Length of line to 100 mm
   • Set G1, Trace gap to 0.2 mm

   

   In the Signal panel, set the following signal parameters:

   • Set Y2, Amplitude to 1.2 V
   • Set TR, Rise time to 100 ps
   • Set TF, Fall time to 100 ps
   • Set PW, Pulse width to 300 ps
   • Set PER, Period to 1 ns

   

4. Run the calculation.

5. To visualize the crosstalk at the far end of the line, do the following:

   • Select Graphs → General parameters in the Calculation results panel
   • Select Port 4 for the Port option in the View settings groupbox.

   

   The results graph at the bottom of the window visualizes the crosstalk waveform at the far end of the line. The crosstalk amplitude is approximately 500 µV.

   

6. To evaluate the crosstalk amplitude relative to the signal amplitude, select both Port 1 and Port 4 for the Port option.

   

   The graph now shows that the crosstalk is negligible compared to the main signal.

   

Calculations for differential transmission lines can be performed in the same way.