# linear amplifier design. when we say an amplifier is linear?

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#### giri_lp

##### Member level 3
linear amplifier design

when we say an amplifier is linear? Is it linear when gain is independent of the input voltage level?

Do we have any other metrics to qualify an amplifier as a linear one?

thanks

linear amplifier design

"Linear" means that the amp behave in a linear way i.e if you draw input-output function, it will be streight line. Output = input * X + B.

Re: linear amplifier design

There are mathematical definitions of the term "linearity" using superposition properties.
But since you ask especially for an amplifier:
An amplifier has linear properties (within a certain range) as long as a sine wave is amplified without any distortion. That means, it appears at the output as an amplified sine wave. Of course, this is an idal case and will never happen in practice.
Nevertheless, we speak of "linear properties" as long as the distortions (measured as THD in %) remain below some specified limits.
In principle, you are right when you assume that in linear systems the gain is constant and independent on the input level - however, the problem is that we cannot use the term "gain" anymore if distortions occur. Because, in this case we would calculate an output/input ratio from to voltages which have not the same shape !

Re: linear amplifier design

yxo said:
"Linear" means that the amp behave in a linear way i.e if you draw input-output function, it will be streight line. Output = input * X + B.

To be exact - linear means that the sum of outputs from two stimulus will be the the same as the output from the sum of stimulus. It gives the conclusion that linear will be only Output = a* Input

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