Operational Amplifiers, or “Op-amps” as they are more commonly called, are linear devices that have all the properties required for nearly ideal DC amplification and are therefore used extensively in signal conditioning, filtering or to perform mathematical operations (hence their name “operational”) such as add, subtract, integration and differentiation.
An ideal Operational Amplifier is basically a three-terminal device which consists of two high impedance inputs, one is called the Inverting Input, marked with a negative or “minus” sign, ( – ) and the other one is called the Noninverting Input, marked with a positive or “plus” sign ( + ). A voltage level applied to only one of these inputs will be amplified if the second input is grounded or held at some fixed voltage level.
Operational amplifiers can have infinite open-loop voltage gain allowing them to operate at their maximum amplification. However this very high open-loop gain causes the op-amp to become unstable so the gain is reduced to a more practical level by using negative feedback.
Negative feedback in electronics refers to taking a small part of the output signal from the amplifiers output and feeding it back either to aid or to oppose the input signal. Negative feedback means that the returning signal has a phase that opposes the input signal and can significantly improve the performance of an operational amplifier.
Operational amplifiers can be connected into two basic configurations, Inverting and Non-inverting.
By connecting the output directly back to the negative input terminal, 100% feedback is achieved resulting in a Voltage Follower (buffer) circuit with a constant gain of 1 (Unity).
Op amps are used in a wide variety of applications and by adding more input resistors to either the inverting or non-inverting inputs, op-amp Voltage Adders, Voltage Subtractors, Integrators and Differentiators can be made.
Differential Amplifier (Subtractor)
The Differential Amplifier produces an output that is proportional to the difference between the 2 input voltages.
Voltage Summing Amplifier
Voltage Adders or Summing Amplifiers are made by adding more input resistors.
The Integrator Amplifier produces an output that is the mathematical operation of integration.
The Differentiator Amplifier produces an output that is the mathematical operation of differentiation.