June 20, 2023 at 9:35 am
Marin Milovac
Subscriber

Hello,

Thank you for your answer.

Bellow I am providing screenshots of TDR and voltage levels of various rise time simulations that I have simulated (1ps, 10ps, 100ps, and 1ns).

1ps:
Voltage levels

TDR

 10ps:
Voltage levels

TDR

 100ps:
Voltage levels

TDR

 1ns:
Voltage levels

TDR


From what I can see the main problem for TDR is the output voltage (red) because the ringing of the output voltage gets translated into noise in the TDR. The ringing is there for 1ps, 10ps, and 100ps. For 1ns there is no ringing but the edge is too slow to get any information about impedance discontinuities. 

Also, two very interesting things that I have noticed:

First is that the resistor input voltage also starts ringing BEFORE the signal propagates to the resistor (especially at fast rise times) seemingly breaking causality:



Second is that for fast rise times voltage rises proportionately to the set rise time for about half of its amplitude, but for the second part of its amplitude it does not rise according to the set rise time:



Any help would be much appreciated.

Marin