How to setup and simulate differential TDR (Time Domain Reflectometry) in Cadence

I want to do differential TDR simulation in cadence virtuoso. I have a differential channel, made of Tlines and interconnects (passive componenets). How to setup the TDR simulation to get impedance over time? I know, I have to terminate both n and p channel with 50 ohm each at the output. I have to do also in the input. But how to connect the step voltage source at the input and get the recuired impedance over time from the channel reflection? Should I connect 2 step voltage source at the input of n and p channel ( one is +1v and another is +1v)? Then how to calculate the impedance at the input from the reflection? Can anyone help me.

Note: I am using virtusos version IC6.1.7-64b.500.4, there is no rflib. So I cannot use Balun ports.

• use an ideal transformer TF as a balun – Tony Stewart Sunnyskyguy EE75 Jul 16 '18 at 13:40
• @TonyEErocketscientist is there any other way other than using balun? – aguntuk Jul 16 '18 at 13:53
• Do you understand that the voltage reflected back is used to derive the impedance and that several small discontinuities that give rise to various reflections are superimposed in time and you have to isolate each one unless your driving signal duration is extremely short. – Andy aka Jul 16 '18 at 13:54
• @Andyaka, yes I somewhat understand the voltage reflection that take account in the calculation of TDR impedance. Now my confusion is in the setup. I will put set response at the input in series with 50 ohm resistors at each n and p ports of the input. Now how to calculate and isolate the differential and common mode impedance? If I denote V1 for the signal net from 50 ohm to input-n and V2 for the signal net from 50 ohm to input-p, then V1-V2 should give me differential voltage. Now from there I need to divide by the current. that should give me impedance. but how to do that? – aguntuk Jul 16 '18 at 14:03
• Have you tried following the poor documentation ? bbs.hwrf.com.cn/downpcbe/TDR-TDT_Simulation_Tutorial-3062.pdf – Tony Stewart Sunnyskyguy EE75 Jul 16 '18 at 18:15