Non Inverting Amplifier (OPAMPs)

A non-inverting amplifier is an OPAMP circuit configuration whose output is in phase with the input signal at the non-inverting input. The input signal is applied at the non-inverting input of the opamp. A non-inverting amplifier also acts as a voltage follower circuit.

The non-inverting amplifiers also have negative feedback which is used to control the gain of the amplifier. Feedback contains a voltage divider circuit that provides a part of the output to the input terminal. This OPAMP has a high input impedance and a low output impedance. This makes it an ideal buffer.

Non-Inverting Amplifier circuit:

The non-inverting amplifier is as shown

• The signal which is to be amplified is applied to the non-inverting +ve input terminal and the inverting input terminal is connected to ground wire resistor R1.
• The input and output voltages are in phase with each other, their phase difference is 0 or 360 degrees.
• The feedback resistor Rf introduces negative feedback at the negative inverting input terminal of the opamp. It makes a voltage divider with a ground resistor.

Expression for closed-loop voltage gain:

To derive expression, we are using an ideal opamp. Input resistor Ri = ♾️, current internet input terminals will have 0 value, (I1 = I2 = 0).

The voltage across R1 is given by

V2 = R1 ÷ [(Rf + R1)] × Vo

As per the concept of virtual short discussed earlier,

V1 = Vs = V2

Substituting the value of b2 in the above expression we get,

Vs = R1(Rf + R1)] ×Vo

Close loop voltage gain,

Avf = Vo/Vs = (R1 + Rf) ÷ R1

Avf = 1 + (Rf÷R1)

Vo = Avf × Vs

Conclusion from the above expression for Avf:

1. The positive sign of the equation indicates that the input and output are in phase with each other.
2. The closed-loop voltage gain is always greater than unity 1.
3. The value of Avf is adjustable it can be adjusted by varying the value of Rf and R1. Generally, a variable resistor is present in place of Arif to adjust the closed-loop gain to its desired value.
4. Avf is independent of the open loop gain of the opamp. It depends only on the value of RF and R1.

Difference between Inverting amplifier & Non-inverting amplifier:

Concept of virtual short:

In a non-inverting amplifier, there is a virtual shot between two input terminals.

It means that there is a short circuit for voltage but an open circuit for current. It is due to the two reasons,

• The value of Rin is infinite there for current at both the input terminals is zero.
• The difference between input voltages (V1 – V2) is zero hence Aol is infinite.

Virtual short is an ideal concept. If we operate the opamp in the linear region, virtual short can give accurate values with -Ve feedback.

As the voltage gain reaches infinity there is a virtual short between the input terminal

Because of virtual short inverting voltage follows non-inverting input voltage. If the input signal at non-inverting terminal changes, then the voltage at inverting terminal also changes by the same amount. This action is called “Bootstrapping“.

OP-AMP tutorial:

• Opamp as Differentiator (active differentiator)

• OP AMP integrator

• Voltage Follower OPAMP or buffer Amplifier

• Non Inverting Amplifier (OPAMPs)

• Inverting amplifier (OPAMPs)

• 741 Op Amp, First Operational Amplifier IC

• What is operational amplifier? basics concepts

• Automatic Battery Charger circuit using LM358 OP-AMP

VI Characteristics of IGBT and it’s Working Principle