Now here we are going to make a feedback circuit. A feedback circuit is a circuit, whose output is given back to input. It can be done for many reasons, which we sill discus in later years. One of the main purpose of feedback register is error correction or comparisons etc.

So lets say we have a configuration in which op amp is set in following configuration

The Unity Gain Non-Inverting amplifier

The simplest configuration of the op-amp is as a unity gain “buffer” amplifier:

The output is connected directly to the inverting input.

An equivalent model can be defined as

Here

v+ = Vi (as V+ is directly connected to the source)

and V-=Vo (as V- is directly connected to source)

Now we know that A is a very large number

Hence we can ignore 1 , due to which the equation becomes

What is the use of such amplifier

One may ask that what is the use of above circuit where Output is equal to input . We can use a single wire for this purpose .

In many circuits , the input voltage is being used by many components , or may be depending on some sensitive sensors, hence the current provided at out put is very weak. The above amplifier is a buffer amplifier , where it increases signal current, while maintain its voltage wave form

The Non-Inverting amplifier with gain

An equivalent model can be defined as

Object find Vo in terms of Vi.

Finding Voltage at the junction , represented by red circle above.

Plugging values of Equation 1 and Equation 2 in equation A

Now we know that A is very large (already discussed), we can make the following assumption

Now as A values is very large as compared to 1, we can ignore 1. Which leads our equation to

Cancelling A

Now the above equation give us a ratio between Vo and Vi, or in other words , it is a ratio between output and input . The ratio between output and input is called gain

Example 1

The following graph shows the Gain curve of amplifier, and shows that the output of this device is linear, hence op Amp can be categorized as Linear Device

Example 2

Solution