Skip to main content
Electrical Engineering

Return to Question

added 13 characters in body
Source Link
Enric Blanco
Enric Blanco
  • 5.9k
  • 6
  • 24
  • 41

I've been trying to solve the ac small signal analysis of this BJT amplifier for a while.

The question asks for the following:

Q.4: For the BJT circuit (Figure 4), the signal source generates ac signal with zero DC. The transistor has \$\beta\$ =100, and ro =20 k ohms  .   

(a) Find RE to establish a DC current of IE= 0.5 mA. Assume VBE=0.7 V for conduction.   

(b) Find RC to obtain VC = 5 V.   

(c) Determine the system voltage gain with RL = 10 k ohms. I

I was able to solve part a and b. I obtained RE = 28.85 kohms and RC = 20.2 kohms. But, I can't seem to solve part c. I used the t-model to try to solve for the gain. I considered Re to be just internal resistance of the amplifier. That is, re= \$ \frac{V_t}{I_e} \$ and I disregarded the previously found value for RE in part a (because of the bypass capacitor in parallel to Re). I eventually got to the answer \$ A_v \$= -99.2 v/v but the answer given by my teacher was \$ A_v \$=-66.26 v/v. 

I've been trying for a couple of hours ( :( ) but I can't seem to be able to solve it. Any ideas?

enter image description here

I've been trying to solve the ac small signal analysis of this BJT amplifier for a while.

The question asks for the following:

Q.4: For the BJT circuit (Figure 4), the signal source generates ac signal with zero DC. The transistor has \$\beta\$ =100, and ro =20 k ohms  .  (a) Find RE to establish a DC current of IE= 0.5 mA. Assume VBE=0.7 V for conduction.  (b) Find RC to obtain VC = 5 V.  (c) Determine the system voltage gain with RL = 10 k ohms. I was able to solve part a and b. I obtained RE = 28.85 kohms and RC = 20.2 kohms. But, I can't seem to solve part c. I used the t-model to try to solve for the gain. I considered Re to be just internal resistance of the amplifier. That is, re= \$ \frac{V_t}{I_e} \$ and I disregarded the previously found value for RE in part a (because of the bypass capacitor in parallel to Re). I eventually got to the answer \$ A_v \$= -99.2 v/v but the answer given by my teacher was \$ A_v \$=-66.26 v/v. I've been trying for a couple of hours ( :( ) but I can't seem to be able to solve it. Any ideas?

enter image description here

I've been trying to solve the ac small signal analysis of this BJT amplifier for a while.

The question asks for the following:

Q.4: For the BJT circuit (Figure 4), the signal source generates ac signal with zero DC. The transistor has \$\beta\$ =100, and ro =20 k ohms. 

(a) Find RE to establish a DC current of IE= 0.5 mA. Assume VBE=0.7 V for conduction. 

(b) Find RC to obtain VC = 5 V. 

(c) Determine the system voltage gain with RL = 10 k ohms.

I was able to solve part a and b. I obtained RE = 28.85 kohms and RC = 20.2 kohms. But, I can't seem to solve part c. I used the t-model to try to solve for the gain. I considered Re to be just internal resistance of the amplifier. That is, re= \$ \frac{V_t}{I_e} \$ and I disregarded the previously found value for RE in part a (because of the bypass capacitor in parallel to Re). I eventually got to the answer \$ A_v \$= -99.2 v/v but the answer given by my teacher was \$ A_v \$=-66.26 v/v. 

I've been trying for a couple of hours ( :( ) but I can't seem to be able to solve it. Any ideas?

enter image description here

Source Link
Ennis
Ennis
  • 101
  • 1
  • 1
  • 1

Determining Voltage gain in a BJT amplifier

I've been trying to solve the ac small signal analysis of this BJT amplifier for a while.

The question asks for the following:

Q.4: For the BJT circuit (Figure 4), the signal source generates ac signal with zero DC. The transistor has \$\beta\$ =100, and ro =20 k ohms . (a) Find RE to establish a DC current of IE= 0.5 mA. Assume VBE=0.7 V for conduction. (b) Find RC to obtain VC = 5 V. (c) Determine the system voltage gain with RL = 10 k ohms. I was able to solve part a and b. I obtained RE = 28.85 kohms and RC = 20.2 kohms. But, I can't seem to solve part c. I used the t-model to try to solve for the gain. I considered Re to be just internal resistance of the amplifier. That is, re= \$ \frac{V_t}{I_e} \$ and I disregarded the previously found value for RE in part a (because of the bypass capacitor in parallel to Re). I eventually got to the answer \$ A_v \$= -99.2 v/v but the answer given by my teacher was \$ A_v \$=-66.26 v/v. I've been trying for a couple of hours ( :( ) but I can't seem to be able to solve it. Any ideas?

enter image description here