Thanks for visiting.
I should design two stage bjt amplifier transistor that consists Audio system in my homework. And i can obtain small signal gain, but cannot obtain large signal gain which includes capacitance (because I convert capacitor short circuit at the small signal analysis)

How can i get Gain and gain bandwidth?

 

Which BJT and what are the values of the components you use?
How much signal gain do you expect to get and how much are you getting?
Are you building the circuit or are you simualting?

Allen

 

Hi,

Normally we ask to see your first try at solving this because not only does that help you learn better it also shows us how your instructor or book material expects you to solve this. There are many approaches to circuit problems and knowing what approach is best could only come from your course work material in almost all cases.

With that in mind and without seeing your initial try at this, i could guess and say that you could probably assume your transistors are ideal current sources with whatever Beta and that Cp combined with the output resistance dominates the roll off response. That would be a typical way to solve this if you are allowed to assume that the transistor transition frequency is significantly higher than the cutoff frequency due to the output resistance and Cp. You could also most likely assume that all the caps except Cp are a short for AC unless their contribution to the response is significant compared to the output resistance and Cp contribution. So you really have to supply more information and hopefully your first try at doing this.

To do it using the above assumptions about the frequency limitations, you could just find the transfer function and then calculate the cutoff frequency or whatever other frequency you want to calculate, such as the 0db frequency. If you've never done these kinds of circuits before that would be a good way to start anyway though, and then later add any other factors into the works if you like. At least that way you'll have an idea how this is done either way.

Also, if you were given actual values like 1k, 1uf, etc., that would be good to know too because that simplifies the problem down to a single solution.

It would also be good to know what approximations you were allowed to use, such as the base emitter voltage drop which you may be able to get away with zero (for example) for this problem because it is mostly an AC problem. Another approximation example is stage gain equal to Rc/Re. We dont know what is allowed until you tell us

 

Normally audio bandwidth is 2 Hz to 20 kHz.

 

Normally audio bandwidth is 2 Hz to 20 kHz.

Hi,

Wow you must be able to hear better than a blue whale

Did you mean 20Hz to 20kHz?

 

Hi,

Wow you must be able to hear better than a bue whale

Did you mean 20Hz to 20kHz?

Yes.