Hi All,
I am struggling a little with Figures 12.21 and 12.22. In lecture 23 we were told that the -D^2/R value of Figure 12.21 was wrong (inverse)... I don't quite follow why...
from 12.53...
-v1hat*I1/V1 term... I1 = D*I2 and I2 = V2/R, so I1 = D*V2/R which results in (D*V2)/(R*V1), V2/V1 = D, so -v1hat*I1/V1 = -v1hat*D^2/R... which is what I think it shows on Fig 12.21
I am running into a similar situation on Fig 12.22...
After perturbation and linearization I get I2*v2hat + V2*i2hat = V1*ichat + Ic*v1hat
which results in a -v2hat*I2/V2 term... since I2 = V/R, V2 = V and v2hat = vhat, I get -vhat/R for the term. It looks like Figure 12.22 shows a +R term for this (Inverse and opposing sign of the equation I get)...
I don't quite follow why both are inverse from what the equations show and why I have a negative term in the Figure 12.22 equation. Everything else matches from what I got...
Can anyone help out to where I went wrong?
Thanks!
Hi Olga,
ReplyDeleteThe small signal model of Fig 12.21 shows the term corresponding to vhat as a resistor. Hence, -R/D^2. If it is -D^2/R (as given in first edition of the text book) -V*R/(D^2)does not result in current units. For 12.22 even i ended up with -R.
You are closer than you realize... Remember that the resistor term is inside the model network and i2 flows out of the network...
ReplyDeleteNow i get it. Thanks Reid.
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