I have this circuit with a CE NPN-BJT amplifier and I am struggling to find the necessary values for calculating r(pi) for AC analysis, i.e. the hybrid-pi model:

$$r_{pi} = \frac{V_{thermal}}{I_b}$$

I need to find the current going into the base of the CE amplifier. I am assuming that the infinite capacitor is also assumed to be a short circuit in DC analysis. This means that V(b) = 0. I can then use the active region model of NPN BJT for DC analysis to write down the KVL which gives me something like this: -0.7 - 60(I[e]) = 0

I solve the equation and end up with a negative emitter current. This does not adhere to the model. What am I doing wrong  ?

![image_1]

I have this circuit with a CE NPN-BJT amplifier and I am struggling to find the necessary values for calculating r(pi) for AC analysis, i.e. the hybrid-pi model:

$$r_{pi} = \frac{V_{thermal}}{I_b}$$

I need to find the current going into the base of the CE amplifier. I am assuming that the infinite capacitance to be short circuited in the DC analysis. This means that V(b) = 0 I can then use the active region model of NPN BJT for DC analysis to write down the KVL which gives me something like this: -0.7 - 60(I[e]) = 0

I solve the equation and end up with a negative emitter current. This does not adhere to the model. What am I doing wrong?

![image_1]

I have this circuit with a CE NPN-BJT amplifier and I am struggling to find the necessary values for calculating r(pi) for AC analysis, i.e. the hybrid-pi model:

r(pi) = V(thermal) / I(b)

I need to find the current going into the B terminal of the CE amplifier. I am assuming that the infinite capacitor is also assumed to be a short circuit in DC analysis. This means that V(b) = 0. I can then use the active region model of NPN BJT for DC analysis to write down the KVL which gives me something like this: -0.7 - 60(I[e]) = 0

I solve the equation and end up with a negative emitter current. This does not adhere to the model. What am I doing wrong?

I have this circuit with a CE NPN-BJT amplifier and I am struggling to find the necessary values for calculating r(pi) for AC analysis, i.e. the hybrid-pi model:

$$r_{pi} = \frac{V_{thermal}}{I_b}$$

I need to find the current going into the base of the CE amplifier. I am assuming that the infinite capacitor is also assumed to be a short circuit in DC analysis. This means that V(b) = 0. I can then use the active region model of NPN BJT for DC analysis to write down the KVL which gives me something like this: -0.7 - 60(I[e]) = 0

I solve the equation and end up with a negative emitter current. This does not adhere to the model. What am I doing wrong  ?

![image_1]