Electronics Operational Amplifiers (OP-AMP)

What is operational amplifier? basics concepts

What is operational amplifier?
An operational amplifier is a DC-coupled high-gain electronic voltage amplifier amplifier that has high gain, differential input, high input resistance, and low output resistance.
It produces an output potential (without feedback) which is typically hundreds of thousands of times larger than the differential input voltage. That’s why it is mostly present in electronics circuits. Operational amplifiers are also called OP-AMP.


The symbol of an OP-AMP is as shown

opamp symbol


Usually, there are five pins in one OP-AMP
Inverting pin
Non-Inverting pin
Output pin
Positive Supply/Bias voltage pin
Negative Supply Voltage/Ground pin

Dual power supply:

Most of the OP-AMP need to a DC power supply. The +Vs and -Vs are power supply terminal.

the +ve terminal of OP-AMP is connected to positive terminal of source and -ve terminal is connected to negative terminal of source.


Ideally, the OP-AMP amplifies the input differential voltage (potential difference between inverting and non-inverting pin).

Vout = AOL(V+ – V)
where AOL is the open-loop gain of the operational amplifier, V+ is the non-inverting input voltage and V is the inverting input voltage.
The gain of an OP-AMP is controllable. External resistor controls the gain of OP-AMPs. If there is no feedback, the gain is called open-loop gain, if the feedback is present the gain is called closed-loop gain.

If there is even a small differential voltage at the input, it will cause an output voltage equal to the almost supply voltage. It is due to the large gain of the amplifier. In open-loop gain, an operational amplifier acts as a comparator (compares the inverting and non-inverting voltage). If non-inverting voltage is greater than the inverting voltage, the output will be almost equal to the supply voltage because

(V+ – V) > 0
So, the output will be positive and equal to supply voltage while if inverting voltage is greater than the non-inverting voltage, the output will be almost equal to the negative supply voltage or ground.

If feedback is present then the gain is  called closed-loop gain. Now, there are two configurations for the operational amplifier
1-inverting OP-AMP
2-non-inverting OP-AMP

Inverting operational amplifier


Inverting operational amplifier

Inverting amplifier is the one which amplifies the signal and also inverts the signal. Its gain formula is

AV = -(Rf/Rin)
The negative sign shows that the signal gets inverted.

Non-Inverting Operational Amplifier:

Non inverting operational amplifier


A non-Inverting amplifier is the one that amplifies the signal without inverting it. Its gain formula is

AV = 1 + (R2/R1)

Ideal Operational Amplifier

The ideal OP-AMP is the one that has the following characteristics.

  • Infinite open-loop gain
  • Infinite input resistance
  • Zero output resistance
  • Zero input offset voltage

No real OP-AMP is ideal because the real OP-AMP does not satisfy the above conditions.

Applications of Operational Amplifier:

In various electronic circuits OP-AMPs are present.

  • Differential Amplifier
  • Differentiators and Integrators
  • Filters
  • Oscillators and waveform generators
  • Precision rectifiers
  • Voltage clamping
  • Analog to digital converters
  • Digital to analog converters

OP-AMP tutorial:


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