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  #1  
Old 10-29-2013, 08:08 PM
Sgt.Incontro Sgt.Incontro is offline
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Default Solving Transfer Function

Hi,

I am stuck on this question...



The current source is throwing me off this, and I do not know exactly how to deal with it.

My answer seems very wrong -> V(0)/i(g) = Zr+Zl, so a hand would be greatly appreciated, as I am really stuck.

Thanks.

Last edited by Sgt.Incontro; 11-02-2013 at 05:38 PM.
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  #2  
Old 10-29-2013, 08:25 PM
Jony130 Jony130 is offline
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Try to use a current divider rule
http://en.wikipedia.org/wiki/Current_divider
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  #3  
Old 10-30-2013, 03:50 AM
WBahn WBahn is offline
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Quote:
Originally Posted by Sgt.Incontro View Post
Hi,

I am stuck on this question...



The current source is throwing me off this, and I do not know exactly how to deal with it.

My answer seems very wrong -> V(0)/i(g) = Zr+Zl, so a hand would be greatly appreciated, as I am really stuck.

Thanks.
Using your answer you have:

V(0) = i(g)(Zr+Zl)

But this would require that ALL of the i(g) goes through the Zr and Zl. What about the portion that goes through Zc?
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  #4  
Old 10-30-2013, 07:06 AM
Sgt.Incontro Sgt.Incontro is offline
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Quote:
Originally Posted by WBahn View Post
Using your answer you have:

V(0) = i(g)(Zr+Zl)

But this would require that ALL of the i(g) goes through the Zr and Zl. What about the portion that goes through Zc?
I knew my answer is incorrect, as it does not make any sense.

If it was an ordinary voltage source instead of current source, you would have:

V(o)/V(i)= (Zl+Zr)/( (Zl+Zr) || Zc )

wouldn't you? So how would deal with the current source?

Sorry if I am heading in the wrong direction.
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Old 10-30-2013, 07:33 AM
WBahn WBahn is offline
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If it was a voltage source, then the transfer function would be exactly 1.

Think about it.

Going back to the original circuit:

Just analyze the circuit. For instance, sum up the currents going into the top node and set that equal to the currents leaving the top node. You know that the voltage on the top node is Vo. What do you get?
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  #6  
Old 10-30-2013, 03:55 PM
Sgt.Incontro Sgt.Incontro is offline
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Quote:
Originally Posted by WBahn View Post
If it was a voltage source, then the transfer function would be exactly 1.

Think about it.

Going back to the original circuit:

Just analyze the circuit. For instance, sum up the currents going into the top node and set that equal to the currents leaving the top node. You know that the voltage on the top node is Vo. What do you get?
You are totally correct about the transfer function being 1 if it was a voltage source. (lol) But is it not possible to do a source transformation?

For the currents:
i(g) = i(c) + i(RL)

and then from there?
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Old 10-30-2013, 04:07 PM
WBahn WBahn is offline
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Quote:
Originally Posted by Sgt.Incontro View Post
You are totally correct about the transfer function being 1 if it was a voltage source. (lol) But is it not possible to do a source transformation?
Sure.

Quote:
For the currents:
i(g) = i(c) + i(RL)
I don't know. You haven't indicated what the reference direction for i(c) and i(RL) and I'm not a mind reader.

Quote:
and then from there?
And then write i(c) and i(RL) in terms of the output voltage.
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Old 10-30-2013, 04:39 PM
Sgt.Incontro Sgt.Incontro is offline
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I tried a source transformation, am I correct in saying the source transformation would result in a voltage source V(g) followed by a series source resistance of Z(c)||( Z(r) + Z(l) )? (And then the rest of the circuit attached to this?)

Quote:
Originally Posted by WBahn View Post
I don't know. You haven't indicated what the reference direction for i(c) and i(RL) and I'm not a mind reader.
I considered both currents facing downwards.

Quote:
Originally Posted by WBahn View Post
And then write i(c) and i(RL) in terms of the output voltage.
How exactly?
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Old 10-31-2013, 09:17 AM
anhnha anhnha is offline
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Hi,
Maybe, I can help a bit.
Quote:
I tried a source transformation, am I correct in saying the source transformation would result in a voltage source V(g) followed by a series source resistance of Z(c)||( Z(r) + Z(l) )? (And then the rest of the circuit attached to this?)
I think it is right. However, what is the purpose for this?

Please see the picture:



1.What is relation between ig, I1, I2? In other words,write the equation that relates ig, I1, I2 through Kirchhoff's Current Law for node A.
2.Express I1 in terms of Vo?
3 Express I2 in terms of Vo?

Substitute I1, I2 expressions you got in #1 and #2 into #1.
Now can you derive Vo/ig?
Attached Images
File Type: png Transfer Function.PNG (20.7 KB, 18 views)
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  #10  
Old 10-31-2013, 03:54 PM
WBahn WBahn is offline
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Quote:
Originally Posted by Sgt.Incontro View Post
I tried a source transformation, am I correct in saying the source transformation would result in a voltage source V(g) followed by a series source resistance of Z(c)||( Z(r) + Z(l) )? (And then the rest of the circuit attached to this?)



I considered both currents facing downwards.



How exactly?
I don't know what happen to the response I thought I had posted. Oh well.

1) What is the voltage across the capacitor?
2) What is the impedance of the capacitor?
3) What is the current through the capactor?

4) What is the voltage across the series combination of R & L?
5) What is the impedance of the series combination of R & L?
6) What is the current through the series combination of R & L?
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