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

• oddjobmj
In summary, the conversation discusses two amplifier circuits in an electronics lab - one inverting and one non-inverting. The reason for choosing R1 and R2 to be about the same for the non-inverting or 'common collector' circuit is to ensure that the base voltage falls between 0 and 10 volts, while the input voltage is between -5 and +5 volts. Inverting amplifiers ground their non-inverting source, while non-inverting amplifiers ground their inverting source. This can be determined by finding the base and collector currents and voltage across the collector or emitter resistances. If the output voltage decreases when a small input voltage is applied, the amplifier is inverting.
oddjobmj

## Homework Statement

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)

## 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!

(A) The emitter follower will only be able to function if the base voltage is between 0 and 10 volts. R1 and R2 are chosen to make that happen, while the input voltage is beteen -5 and +5 volts.

(B/C) those grounded non-inverting/inverting sources happen with opams, and they are not relevant here.

To find out wether an amplifier is inverting:
1 - find out what the base voltage is with no input signal $V_0$
2 - now apply a small input voltage ΔV, so the base voltage is at $V_0 + \Delta V$
3 - now find out what the base current in case 1 and case 2.
4 - same for the collector current in both cases
5. same for the voltage across the collector resistance (common emitter) or emitter resistance (emittor follower)
6. from the results in 5. you can find v-out in both cases. If v_out goes down when ΔV is positive, you have an inverting amplifier

1 person

## 1. What is the difference between an inverting and non-inverting amplifier?

An inverting amplifier has its output signal inverted in relation to the input signal, while a non-inverting amplifier has the same polarity for both input and output signals. This means that a positive input signal will result in a negative output signal for an inverting amplifier, and a positive output signal for a non-inverting amplifier.

## 2. How does an inverting amplifier work?

An inverting amplifier uses an operational amplifier to amplify the input signal while also inverting its polarity. This is achieved by connecting the input signal to the inverting input of the operational amplifier and providing a feedback loop from the output to the inverting input.

## 3. What is the gain of an inverting amplifier?

The gain of an inverting amplifier is determined by the ratio of the feedback resistor to the input resistor. It can be calculated using the formula -Rf/Rin, where Rf is the feedback resistor and Rin is the input resistor.

## 4. What are the advantages of using a non-inverting amplifier?

Non-inverting amplifiers have a high input impedance and low output impedance, which makes them suitable for use with high impedance input signals. They also have a low noise level and provide a more accurate output signal compared to inverting amplifiers.

## 5. Can an inverting amplifier be used as a non-inverting amplifier?

Yes, an inverting amplifier can be converted into a non-inverting amplifier by adding a feedback resistor from the output to the non-inverting input. This will result in a positive output signal for a positive input signal, making it function as a non-inverting amplifier.

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