Hi all, Back again with another BJT configuration, this time it is a Common base question. I am asked to final suitable values for and with a quiescent point I have tried doing Thévenin on each of the terminals but end up with both and in the equation. As well as using my regular method of Im having a mental block and cant seem to find on its own first. Please find attached the question and my attempt at solving it
Given Vb is 0V then Ve will be -0.7V. With Vceq=5V then Vc=+4.3V. This will lead you to Vcc since you are given Ic=1mA & Rc=2k2.
Brilliant, thank you I think i did it right, I ended up with Vcc as 6.5V when i did: Vcc = Ic*Rc + Vc I assumed that it was correct, so I moved on and continued to do most of the questions. Turns out that the common base AC analysis is quite similar to the common emitter i think. I did what i believe is an alpha model of the question...
Ok, I have finished off the question now The two major things that i would like some one to look over is the AC analysis circuit that i drew and the last section where it ask to calculate the transresistance gain What i did was replaced with so that the equation came down to but my answer is very large which doesnt look right
I would dispute both your values of voltage gain and input resistance. To find Av one would use Rc||Rload=2.2k||4.7k=1.5k Also keep in mind that Vo and Vi will be in phase for the CB configuration - at midband frequencies. Also the effective input resistance at the emitter is dominated by re which is quite small. RE and re are in parallel rather than in series as your analysis suggests. Re-check your values.
thanks for pointing that out, i can now see that i did forget to include the load resistance. I changed my values. i now have smaller values for both voltage and current gain.