- #141
yungman
- 5,755
- 292
Read the bias scheme in Malvino. Re2 is to stabilizing the collector current. This is called voltage divider bias. R1 and R2 form a voltage divider to give about 1.7V at the base. The emitter is about 0.7V below so the emitter is at about 1V. You have Re1+Re2 about 200 ohm ( don't be picky), so you are setting up the emitter current ( collector current) of about 5 mA. This 5 mA will give r'e ≈ 5 ohm. The point of using voltage divider bias is to control the current through the BJT by the voltage drop across the Re2. This make it a lot more predictable. Read Malvino, it's all there.
The C2 is to bypass Re2 at frequency you want to amplify. At high frequency, Re2 is being shorted out by C2, so the resistance on the emitter side is r'e+Re1=19 ohm or 20 ohm.
No matter how the circuit looks like, in common emitter BJT circuit, the gain is the total impedance at the collector divided by the total impedance at the emitter. AND it is inverted. It is just that simple.
I just went back and looked at page 5, 6 7 of this thread, Jony130 really...REALLY spent the time explained to you on this. You really need to spend less time asking question here and more time reading the book over and over, work out the problems. I don't have the book, I think it has answers even if you can't find the solution manual. I learn all these from Malvino in 1979 without the solution manual. You are spending almost a month on this and I am sure it's cover in only about 4 to 5 pages in Malvino. I am sure anything I said at this point, HAD been totally covered by Jony130. Read the book over and over and over until you understand. Or read this thread over and over. Write out everything Jony130 wrote step by step to verify that you are following, don't just read, write it out.
The C2 is to bypass Re2 at frequency you want to amplify. At high frequency, Re2 is being shorted out by C2, so the resistance on the emitter side is r'e+Re1=19 ohm or 20 ohm.
No matter how the circuit looks like, in common emitter BJT circuit, the gain is the total impedance at the collector divided by the total impedance at the emitter. AND it is inverted. It is just that simple.
I just went back and looked at page 5, 6 7 of this thread, Jony130 really...REALLY spent the time explained to you on this. You really need to spend less time asking question here and more time reading the book over and over, work out the problems. I don't have the book, I think it has answers even if you can't find the solution manual. I learn all these from Malvino in 1979 without the solution manual. You are spending almost a month on this and I am sure it's cover in only about 4 to 5 pages in Malvino. I am sure anything I said at this point, HAD been totally covered by Jony130. Read the book over and over and over until you understand. Or read this thread over and over. Write out everything Jony130 wrote step by step to verify that you are following, don't just read, write it out.
Last edited: