# Transistor/Amplifier pre-lab; Inverting vs Non-inverting

1. The problem statement, all variables and given/known data
There are two amplifier circuits in my electronics lab. I know one is inverting and one is not but I can’t put my finger on why.

(A) I have to explain why R1 and R2 are about the same for the emitter follower (non-inverting / ‘common collector’).

I also need to (B) explain why the inverting is an inverting amplifier and (C) why the non-inverting is a non-inverting amplifier.

Common-Emitter (inverting)

Common-Collector (non-inverting)

2. Relevant equations

3. The attempt at a solution
(A)
In my notes I have that usually R1≈R2 but my prof. didn’t say why. My understanding is that for this type of amplifier you actually don’t want a voltage amplification. The use of the amplifier is to go from a weak signal to a strong signal. I would imagine the ratio of these resistors has something to do with that but I can’t put my finger on why that is the case. Is it because:

Av=$\frac{ΔV_{out}}{ΔV_{in}}$=$\frac{ΔV_{E}}{ΔV_{B}}$

To make sure that VE and VB are the same we removed the RC resistor and made the other two the same?

(B)/(C)
I read that inverting amplifiers ground their non-inverting source and don’t ground their inverting source. The alternative seems to be true for non-inverting amplifiers. This doesn’t seem to be clear in the schematic though. Is there some other reason? If not, any suggestions as to how I can view this schematic in that sense?

Thank you!

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