# Homework Help: Low signal circuit analysis

1. Apr 13, 2013

### Drao92

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• ###### Circuit.png
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2. Apr 13, 2013

### Staff: Mentor

3. Apr 14, 2013

### Drao92

Sure
The DC source is above the T3 transistor and resistor, i forgot to draw it.
The problem i have is that i cant 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 couldnt find any.
https://www.physicsforums.com/attachment.php?attachmentid=57846&stc=1&d=1365923347

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• ###### Circuit2.png
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4. Apr 14, 2013

### Staff: Mentor

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...

5. Apr 14, 2013

### Drao92

I study amplifiers. Yes, its a zener diode.
The standard textbook is not in english and it doesnt 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 dont 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 dont 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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• ###### Circuit3.png
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Last edited: Apr 14, 2013
6. Apr 14, 2013

### rude man

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.