PSpice opamp and variable questions

[IlyaZ]

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?

 

[Valkarie]

Homework Equations No equations, just need to know if the solution is plausible. The Attempt at a Solution Yes, this solution should work. By connecting the top dC to an opamp with a gain of 1, the current will only flow in one direction and the voltage will eventually add up to a good graph. This should give the desired damping for l (m) of cable. Additionally, you could use variables to represent the switches and Vdcs which would make the simulation more efficient.

 

[piercas]

I would first commend the approach of using PSpice to model the coaxial cable and investigate its behavior. This is a valuable tool in understanding the characteristics of a system and can help in predicting its response in different scenarios.

In regards to the issue with the switches and the voltage probe, it is likely that the problem lies in the timing of the switches. The switches need to be accurately timed in order to properly simulate the behavior of the cable. I would suggest double-checking the timing settings and making sure they are accurately represented in the simulation.

As for the proposed solution of using an opamp and feedback to simulate the cable, it could work but it may also introduce other variables and complexities that may affect the accuracy of the simulation. It would be important to carefully consider the design and parameters of the opamp and its impact on the overall system.

Another approach could be to use variables in the simulation, such as using a variable resistor to represent the cable segment. This would allow for more flexibility and control in adjusting the damping factor of the cable.

In conclusion, PSpice is a powerful tool for modeling and understanding complex systems, but it is important to carefully consider all the parameters and variables in order to accurately simulate the behavior of the system.