# PSpice opamp and variable questions

1. Homework Statement

We're modelling a coax-cable. This is the first cable segment (/m):

.. ----._.----./. ----dR1----dL-----------........
..|..........................................|........|........
Vdc.......................................dR2....dC8.......
..|..........................................|........|.........
..-------------------------------------------GND

.... Empty Space

A short DC pulse is sent. The first switch is open at t=0 but closes at 1ns (at least so I hope: TCLOSE=1ns) . The second switch opens after 2ns.

But when I put a probe between the switches I see 0V from 0ns to 2ns when there should be a voltage at around 1ns (switch time is like 0.0001ns). It depends on the other switch, which is strange.

We want to know the damping for l (m) of cable, and this has to be done through PSpice.

We don't want to copy the part without the switches and Vdcs 100 times so we came up with a solution where we do some feedback by connecting the top dC to a non-inverting opamp (with a gain of 1), where the inverting input is connected to GND and the opamp output connected to the right of the second switch. That way the current will only go one way we hope and eventually add up to a good graph. Will this work and are there other ways to do this? Maybe with variables?

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