Transistor problem

Thread Starter

nahid5692001

Joined Mar 8, 2011
5
Hello,

I need some assistance with a HW problem. The specifications are to be these below for transistor:

input voltage is given
gain is high
input resistance high
output resistance low

i know this cannot be done with just one transistor. how many are need? and what configuration do you think?

im thinking a CB with a CC. The CB will output high gain and CC will output gain = 1 so all gain will come from CC, so we can control that with resistors. The CC works well with input and output resistances.

What do you guys think?

Regards
Nanja
Bangalore, India
 

t_n_k

Joined Mar 6, 2009
5,448
Post the specific amplifier design goal values and show some attempt at your working - then you will probably receive some helpful responses.
 

Thread Starter

nahid5692001

Joined Mar 8, 2011
5
I just want to know if my theory is correct. Those are the requirements and with my understanding i should use a CB cascaded with a CC.

I just want to know if i am correct on this via my specs.
 

Adjuster

Joined Dec 26, 2010
2,147
You have been asked for a high input resistance, but you have chosen a common-base input stage.

The common-base configuration has the lowest input resistance.

Think again. What sort of input stage is needed?
 

Thread Starter

nahid5692001

Joined Mar 8, 2011
5
hello,
your absolutely right. i need to switch what i have now. so the CC can be first then the CB. this will work because rout is low and CB has low.

how about that?
 

Adjuster

Joined Dec 26, 2010
2,147
The output impedance of a common-base stage is not low. Also, the common-base stage will put a heavy load on the common-collector input stage, so that its input impedance would not be particularly low.

I think the best thing for you to to would be to write a table of the characteristics of each of the three configurations, so that you are clear about them. If there are things you are not sure of, check up with your study texts or use the internet.

You may find that the ideal solution to this problem requires more than two transistors.
 
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