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Basic Operational Amplifier Circuit and Voltage Gain

An operational amplifier, or op amp, is an electronic component that performs basic amplification functions in a simple integrated circuit (IC). It combines the individual transistors and resistors of a general-purpose amplifier into a small "black box" design having three terminals: an inverting input, a non-inverting input and an output. By adding two resistors to an op amp, you can make a simple voltage gain circuit.

Operational Amplifier
- As many useful, though complex, circuits need amplifiers to manage electronic signals, op amps make life easier for an electronic designer. Using op amps as building blocks, she can construct circuits to convert, add, multiply and compare voltages and currents. Op amps are also indispensable for making signal filters, oscillators and other signal-processing and generating circuits. By combining an op with external components, you "program" it to perform a variety of tasks.
Feedback
- By itself, an op has an infinite voltage gain. Any voltage you put on its inverting or non-inverting input produces a corresponding signal at its output equal to the power supply voltage. Though this has its uses, you typically want to accurately follow small variations in signal strength, such as for amplifying music. You program an op amp's gain by placing a feedback resistor between the inverting input and the output. This way, a small amount of the output signal finds its way back to the inverting input. The amount of gain depends on the resistor's ohm value: a small ohm value produces a small gain, a large value gives more gain.
Inputs
- The op amp's two inputs give you choices as to how you want the amplifier to work. A positive signal at the non-inverting input produces a positive output. At the inverting input, it gives a negative output. Both inputs can work for audio, though the inverting input will give an output 180 degrees out of phase. For direct current (DC) signals, the phase of the signal is more important, so your choice of input matters.
Non-Inverting Amplifier
- A basic non-inverting op-amp circuit that gives a positive voltage gain uses two resistors: one at the input and one for feedback. The input resistor connects the inverting input and the signal common wires. To find the amplifier's voltage gain, you divide the ohm value of the feedback resistor by the value of the input resistor and add one. For example, if the feedback and input resistors have equal ohm values, their quotient is one. Add one to one and get a voltage gain factor of two. A voltage input of zero gives you zero volts at the output. An input of one volt yields two output volts.

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