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Thursday, 4 July 2019

Non- Inverting Mode Amplifier


Non- Inverting Amplifier

A voltage follower (also called a unity-gain amplifier, a buffer amplifier, and an isolation amplifier) is an op-amp circuit which has a voltage gain of one. Voltage followers are generally used to isolate stages from each other. A voltage follower generally has high input impedance and low output impedance.
If the signal is applied to the non-inverting input terminal and feedback is given as following figure, the circuit amplifies without inverting the input signal. Such a circuit is called non-inverting amplifier. It may be noted that it is also a negative feed-back system as output is being fed back to the inverting input terminal.



As the differential voltage vd at the input terminal of op-amp is zero, the voltage node a in above figure is vi , same as the input voltage applied to non-inverting terminal. Now Rf and  R1 forms a potential divider. Hence



as no current flows into the op-amp



non-inverting amplifier is an op-amp circuit configuration which produces an amplified output signal. This output signal of non-inverting op amp is in-phase with the input signal applied. In other words a non-inverting amplifier behaves like a voltage follower circuit.


voltage follower (also called a unity-gain amplifier, a buffer amplifier, and an isolation amplifier) is an op-amp circuit which has a voltage gain of one. Voltage followers are generally used to isolate stages from each other. A voltage follower generally has high input impedance and low output impedance.

The basic non-inverting amplifier circuit using an op-amp is shown above. In this circuit the signal is applied to the non-inverting input of the amplifier. However the feedback is taken from the output via a resistor to the inverting input of the operational amplifier where another resistor is taken to ground. It is the value of these two resistors that govern the gain of the operational amplifier circuit.
The gain of the non-inverting amplifier circuit for the operational amplifier is easy to determine. The calculation hinges around the fact that the voltage at both inputs is the same. This arises from the fact that the gain of the amplifier is exceedingly high. If the output of the circuit remains within the supply rails of the amplifier, then the output voltage divided by the gain means that there is virtually no difference between the two inputs.
As the input to the op-amp draws no current this means that the current flowing in the resistors R1 and R2 is the same. The voltage at the inverting input is formed from a potential divider consisting of R1 and R2, and as the voltage at both inputs is the same, the voltage at the inverting input must be the same as that at the non-inverting input. This means that Vin = Vout x R1 / (R1 + R2). Hence the voltage gain of the circuit Av can be taken as

Applications:


Op amp as a voltage follower

A non-inverting amplifier using an op amp forms an ideal voltage follower. The very high gain of the op amp enables it to present a very high impedance to the signal source whilst being able to accurately follow the voltage waveform.
An op amp is configured in its non-inverting amplifier format, linking the output directly to the inverting input and applying the input signal to the non-inverting input.

From the gain equation it is possible to see that the voltage gain of this circuit is unity.
Av = 1 + R2 / R1.
R2 is zero and R1 is infinity,
So the term R2/R1 is zero and this means that Av = 1 (Unity Gain)




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