BJT op amp equivalent circuit AC and DC analysis.

Thread Starter

hiphop

Joined Oct 10, 2016
5
We have to find the overall voltage gain of this circuit i.e Ad=V0/(V1-V3).1.jpg
I have found the collector currents through each resistor except for transistors Q7 and Q8.2.jpg
Also I have found the voltage gain for the first stage(consisting of Q1,Q2,Q3 and Q4) and the second stage (Q5 and Q6).3.jpg 4.jpg
Now I know that to find the total voltage gain , I have to multiply the voltage gain of each stage taking in account the input resistance of the next stage .
But how do I find the voltage gain and input resistance of the third stage (Q7 and Q8).
 

The Electrician

Joined Oct 9, 2007
2,971
Since there is no circuitry to bias both Q7 and Q8 into their linear operating region simultaneously, only one of Q7/Q8 will be on when the output is more than .7 volt above or below ground. For a complementary class B emitter follower like this, it would be a reasonable approximation to say that the Q7/Q8 voltage gain is unity, and the input resistance is just β times the output load resistance. The Q7/Q8 output circuit will produce substantial crossover distortion.
 
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Thread Starter

hiphop

Joined Oct 10, 2016
5
Since there is no circuitry to bias both Q7 and Q8 into their linear operating region simultaneously, only one of Q7/Q8 will be on when the output is more than .7 volt above or below ground. For a complementary class B emitter follower like this, it would be a reasonable approximation to say that the Q7/Q8 voltage gain is unity, and the input resistance is just β times the output resistance. The Q7/Q8 output circuit will produce substantial crossover distortion.
Thank you for replying.Also is the formula for Ad1(no load) and Ad2 (no load)correct.
 

Thread Starter

hiphop

Joined Oct 10, 2016
5
Your handwriting (the calculations, not the text) is too hard for me to read, so I can't offer an opinion about the correctness of Ad1 and Ad2.
Sorry for that , anyway I did the calculations again and it is correct.
Also can you recommend a book which deals with differential amplifiers , op amps and their quantitative analysis .
 
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