# How can I calculate the gain and impedance of the given circuit?

Discussion in 'Homework Help' started by Mustafa Simsek, Apr 6, 2015.

1. ### Mustafa Simsek Thread Starter New Member

Apr 6, 2015
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0
Hello I was designing an amplifier for a homework and I did some research and found a circuit that does my circuits job very well but I don't know how should I calculate the voltage and current gain at this part of the general circuit. Can you help me please?
It is emergency !!! :/

2. ### Papabravo Expert

Feb 24, 2006
10,340
1,850
That's a problem with finding a circuit. Tell us how you think you should go about it, using hand calculations or the simulator.

3. ### Mustafa Simsek Thread Starter New Member

Apr 6, 2015
6
0
I'm designing an amplifier for standard audio input 1 mW average on 600 ohms to convert 2W output with a 8 ohm load. First transistor is for current gain and impedance matching. Second one is for voltage gain. I can calculate until here. The problematic part is that there is the output of voltage gain part of the circuit coming through C2 to the last part of the circuit. Last part of the circuit is increasing the current very well but I have to calculate the current and voltage gain at here.

4. ### Papabravo Expert

Feb 24, 2006
10,340
1,850
Yes I know what it is you are looking for, and I'm asking you how would you propose going about it. Don't you have two stages in parallel being combined to make the output. Is that a good place to start?

5. ### Mustafa Simsek Thread Starter New Member

Apr 6, 2015
6
0
Yes I do have two stages in parallel being combined to make the output. So one side is amplifiying the + side of the signal and other side is amplifiying the - side of the signal by using two stages. I just dont understand the gain formula of that system.

6. ### Papabravo Expert

Feb 24, 2006
10,340
1,850
Do you think you can get to the answer by analyzing one of the stages? What gain formula do you have? Can you use the simulator to cross check your answer?

7. ### Mustafa Simsek Thread Starter New Member

Apr 6, 2015
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0
I dont think I can handle with two stages. I have formulas but they are not so meaningful right now for me :/

8. ### Papabravo Expert

Feb 24, 2006
10,340
1,850
The way gain is supposed to work, if you have two stages cascaded then you multiply the gains together - right?

9. ### Mustafa Simsek Thread Starter New Member

Apr 6, 2015
6
0
Yes we can multiply the gains together and we can think that two stages transistor set as one transistor but in this case how can I shorten it like? I mean if I draw two stages as one transistor, for my case how should I draw the circuit?
Edited: Also how can I calculate the resistance of the selected circuit. To calculate the second circuit's gain I have to know the impedance of the selected third circuit. How should I calculate it?

10. ### Mustafa Simsek Thread Starter New Member

Apr 6, 2015
6
0
I understood the solution of third part of my circuit by watching the following video's 14:37 mins:secs. Can you help meto calculate the impedance of the third circuit? ^^

11. ### Jony130 AAC Fanatic!

Feb 17, 2009
3,991
1,115
I do not see any video ?? Also notice that Q1, Q3 and Q5 ,Q6 are not think more then a voltage followers.
Do you know the equations for Rin and voltage gain for a voltage follower ?
What I can tell you for sure is that Rin will be smaller than R3||R4 and the gain is less then one

12. ### WBahn Moderator

Mar 31, 2012
18,087
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Do you know how to transform this circuit into its small signal equivalent?