How Everything Works
How Everything Works How Everything Works

Question 1111

How does an operational amplifier work? — BR
An operational amplifier is an extremely high gain differential voltage amplifier—a device that compares the voltages of two inputs and produces an output voltage that's many times the difference between their voltages. How the operational amplifier performs this subtraction and multiplication process depends on the type of operational amplifier, but in most cases two input voltages control how current is shared between two paths of a parallel circuit. Even a tiny difference between the input voltages produces a large current difference in the two paths—the path that's controlled by the higher voltage input carries a much larger current than the other path. The imbalance in currents between the two paths produces significant voltage differences in their components and these voltage differences are again compared in a second stage of differential voltage amplification. Eventually the differences in currents and voltage become quite large and a final amplifier stage is used to produce either a large positive output voltage or a large negative output voltage, depending on which input has the higher voltage. In a typical application, feedback is used to keep the two input voltages very close to one another, so that the output voltage actually falls in between its two extremes. At that operating point, the operational amplifier is exquisitely sensitive to even the tiniest changes in its input voltages and makes a wonderful amplifier for small electric signals.

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