2 Replies Latest reply on Jan 8, 2014 9:09 AM by potluri.ravikumar

    Normalization/Reference Impedance




      Could you suggest me how to select reference impedance (Convert->Renormalize) for an S-Parameter model of a power plane extracted by converting Z-Parameters plot from decoupling analysis?, I am asking this question because when I select reference normalization impedance to be 0.1 Ohm it gives S21 with for e.g.: -40dB and if I select normalization impedance to be 0.01 Ohm it gives S21 for e.g.: -25dB. Why is this difference and how to select suitable normalization impedance for a power plane. I know that normalization impedance for a SE tranmission line is 50Ohms.




        • 1. Re: Normalization/Reference Impedance

          Hi Ravi,


          Either one will work fine as the simulator will know from the Touchstone file what was the value of the reference impedance. Accordingly to the Touchstone spec 11, pages 4 and 5, the data file must contain an option line formatted as follows:

          # <frequency unit> <parameter> <format> R <n>

          R n specifies the reference resistance in ohms, where n is a positive number of ohms (the real impedance to which the parameters are normalized). The default reference resistance is 50 ohms.


          Here is an example from a PDN Z-parameter extracted using HyperLynx:


          ! HyperLynx V8.1-64 SI-SPICE V2010.06.16

          # HZ Z  RI R 1.000000e-001




          • 2. Re: Normalization/Reference Impedance

            Hello Cristian,


            What I am trying to do here is to cross check the DC drop from S-Parameter simulation data and find out reference impedance. I did DC drop simulation between VRM and Load and simulation suggests DC resistance of the path to be around 10mOhms. Please find the file attached. The S21 magnitude from a series R resistance with Zo reference impedance is 1/(1+R/(2*Zo)). Assuming that the actual correct DC resistance value is 10mOhms, the S21 magnitude is around -0.5dB and with Zo = 0.1Ohm and -3dB with Zo=0.01Ohm. So, is this the way to select reference impedence of a S-Parameter model of a power plane if we want to do transient analysis to find out power supply noise?


            Thanks and Regards,