Here's a breakdown:
* Linearity: In a linear system, the output is a scaled version of the input. This means that doubling the input will double the output, tripling the input will triple the output, and so on.
* Op-Amp Behaviour: Ideal op-amps are designed to amplify the difference between their two input terminals (inverting and non-inverting). This difference, known as the differential input voltage, is amplified by a large gain factor (typically 100,000 or more). This means that even tiny input voltage differences produce significant output voltage changes.
* Linear Relationship: Within the op-amp's operational range, the output voltage is linearly proportional to the input voltage difference. This relationship is maintained as long as the op-amp is not saturated (reaching its maximum or minimum output voltage).
Important Note: Real-world op-amps exhibit slight non-linearity due to factors like:
* Input Offset Voltage: A small voltage difference that exists between the input terminals even when there's no input signal.
* Slew Rate: The maximum rate of change of the output voltage, which can limit the op-amp's ability to faithfully reproduce high-frequency signals.
* Distortion: At high input signal levels, op-amps can introduce distortion, meaning the output signal is not an accurate representation of the input.
However, these non-linearities are typically small enough that op-amps are still considered linear devices for most practical applications.
Conclusion:
While op-amps do have some non-linear characteristics, their ability to amplify the input signal linearly over a wide range justifies their classification as linear devices. This linear behavior is crucial for their use in various analog circuits, including amplifiers, filters, and oscillators.