Why is T2 removed in low signal circuit analysis?

AI Thread Summary
In low signal circuit analysis, T2 can be removed because it functions primarily as a current mirror, which is not needed for AC analysis. The discussion highlights confusion regarding the role of T1 and T3 transistors, with T3 acting as a DC current source and having infinite impedance in AC analysis. The participants emphasize the importance of understanding which components can be disregarded when transitioning from DC to AC analysis. Recommendations for textbooks on transistor analysis are made, although language barriers pose challenges for some users. Understanding these concepts is crucial for calculating parameters like Vo/Vi, Rin, and Rout in amplifier circuits.
Drao92
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Sure
The DC source is above the T3 transistor and resistor, i forgot to draw it.
The problem i have is that i can't understand what parts of the circuit i have to remove when i move from DC analysis to AC analysis. Can you recommend me a book or some documentation which explains this because i couldn't find any.
https://www.physicsforums.com/attachment.php?attachmentid=57846&stc=1&d=1365923347
 

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Drao92 said:
Sure
The DC source is above the T3 transistor and resistor, i forgot to draw it.
The problem i have is that i can't understand what parts of the circuit i have to remove when i move from DC analysis to AC analysis. Can you recommend me a book or some documentation which explains this because i couldn't find any.
https://www.physicsforums.com/attachment.php?attachmentid=57846&stc=1&d=1365923347

What is the component connected below the base of T2? Maybe a Zener diode?

What class is this for, and what is the standard textbook? Most textbooks on standard transistor analysis should cover how to analyze this circuit...
 
I study amplifiers. Yes, its a zener diode.
The standard textbook is not in english and it doesn't cover these things.I made these on seminars
Ill post another example.
So, the T2 and T3 transistors make a DC source and its a ground in AC, but i don't understand why the T1 transistor is a ground too. This is the problem i have.
After i make the AC circuit i have to calculate Vo/Vi, Rin, Rout, very easy but if i don't know how to make the AC circuit is useless .
https://www.physicsforums.com/attachment.php?attachmentid=57856&stc=1&d=1365959633
 

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T3 is not a ground for AC. In fact, it's infinite impedance (theoretically) for AC. It's a source of dc current. A current source has infinite impedance. In fact, the collector of T3 is your input voltage point.

T1 is also a current source. The function of T2 is to mirror the current through its collector to the collector of T3. T1 defines the collector current for T2 and trerefore for T3 also. T3 defines the operating point of the grounded-gate JFET amplifier.
 

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