# PSpice AC Frequency Sweep of Transfer Function

Discussion in 'Homework Help' started by jegues, Jan 20, 2011.

1. ### jegues Thread Starter Well-Known Member

Sep 13, 2010
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Hello all,

I'm trying to figure out how to use PSpice to analysis this circuit,

I've already completed nodal and mesh analysis on this circuit and have derived the same transfer function. (This was done in a previous thread)

I also found the output voltage vo(t) if vin(t) = 0.001Vu(t) for t>0.

Here's what I've got in PSpice so far,

Here's my design for the circuit in the first picture. Now a few questions about the design itself before I get into the gritty details of the simulation. What kind of voltage source component should I be using for Vin? The logo is an AC source in the diagram but it's simply a step source right? Would I be fine wiring in a DC source with 0.001V? (The simulation and analysis portion is only concerned for t>0) In addition to this, did I use the correct current controlled current source component? To obtain the $\beta$ factor with my controlling current I simply double clicked on the component and changed the "COEFF" value from 1 to 100. (Since $\beta$ is given as 100)

With these things sorted out the design of my circuit should be okay. (Unless there are some other problems that come up?)

Now onto the simulation. I google'd around for a tutorial and found this, http://www.ee.nmt.edu/~rison/ee321_fall02/Tutorial.html

I tried to follow it as closely as possible but it was hard because my PSpice is the demo version that comes with my textbook and it is also newer.

I created a New Simulation profile and change the Analysis type to AC Sweep/Noise.

I inserted my Start and Stop Frequencies as well as the Points/Decade.

As you can see I'm getting 0V across the right most portion of my circuit, so I won't be obtaining the correct transfer function from this simulation.

Can someone help me conduct a proper "AC frequency sweep of the transfer function |T(jw)|" ?

I'm willing to post more photos if need be or answer any questions about what I've done so far.

I'd really like some help on this one!

Thanks again!

EDIT: I tried again with Multisim 10 and here's what I've come up with.

Below is the circuit designed in multisim,

Since my input is just the step function, should I be using an AC source? If so, how do I decide what frequency? (We weren't specified one)

Also, here's the graph I obtained from AC analysis. I don't know if this corresponds with the circuit I've modeled. The Red line is the input and the Blue line is the output.

Also, should the gain on my current controlled be 100? (Is that what the $\beta$ factor is doing?)

Also I still can't figure how to plot the transfer function |T(jw)|, how do you plot Vout vs Vin?

Thanks again!

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• ###### MultisimGraph.JPG
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Last edited: Jan 20, 2011