le Vas he re above shows the voltage-current characteristics of a BJT and how amplification a is obtained. For the sake of clarity, we use upper/lower case letter convention su e + Upe where ugg shows the instantaneous value of the signal which is compose e Veg and AC value Vhe Superimposed on the DC value. Through the course, we he circuits assuming the AC value is very small so that the instantaneous signal i the DC value. In order words, the change of operating point values due to the AC ible. Because of that, we will use small-signal models and parameters and we wil und the DC operating point hence we will use slope (or derivative) at that point.

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2)
Slope = R
le
Va
The figure above shows the voltage-current characteristics of a BJT and how amplification
operation is obtained. For the sake of clarity, we use upper/lower case letter convention such that
Ugg = Vgg + Upe where Vag shows the instantaneous value of the signal which is composed of a
DC value Veg and AC value ve superimposed on the DC value. Through the course, we will
analyze the circuits assuming the AC value is very small so that the instantaneous signal is very
close to the DC value. In order words, the change of operating point values due to the AC signal
is negligible. Because of that, we will use small-signal models and parameters and we will find
them around the DC operating point hence we will use slope (or derivative) at that point. We call
the current and voltage values at a particular DC operating point as quiescent current and
quiescent voltage.
"BE
Remember that for a BJT in forward active region, ic = Ige VT which is the analytical expression
of the given figure. Assume that we biased the BJT at the point where VE = Vae,qand le = Ic.o-
Now we want to find the slope at that particular point and we call it as transconductance gm. Find
the expression for gm
aE lu=Vero: Your final expressions must include quiescent
ic- Ice
voltage/current values and it must agree with the characteristics given in the figure. Comment on
how quiescent point values affect the transconductance. (If you change your Q point from left to
right in the figure, how does gm change? Is this expected from the slope of the characteristics?)
Transcribed Image Text:2) Slope = R le Va The figure above shows the voltage-current characteristics of a BJT and how amplification operation is obtained. For the sake of clarity, we use upper/lower case letter convention such that Ugg = Vgg + Upe where Vag shows the instantaneous value of the signal which is composed of a DC value Veg and AC value ve superimposed on the DC value. Through the course, we will analyze the circuits assuming the AC value is very small so that the instantaneous signal is very close to the DC value. In order words, the change of operating point values due to the AC signal is negligible. Because of that, we will use small-signal models and parameters and we will find them around the DC operating point hence we will use slope (or derivative) at that point. We call the current and voltage values at a particular DC operating point as quiescent current and quiescent voltage. "BE Remember that for a BJT in forward active region, ic = Ige VT which is the analytical expression of the given figure. Assume that we biased the BJT at the point where VE = Vae,qand le = Ic.o- Now we want to find the slope at that particular point and we call it as transconductance gm. Find the expression for gm aE lu=Vero: Your final expressions must include quiescent ic- Ice voltage/current values and it must agree with the characteristics given in the figure. Comment on how quiescent point values affect the transconductance. (If you change your Q point from left to right in the figure, how does gm change? Is this expected from the slope of the characteristics?)
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