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Question about linear amplifiers

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Full Member level 3
Jan 31, 2006
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So a linear amplifier amplifies the signal and the noise powers by the same gain factor. And on top of that, the amplifier adds in its own noise. So the signal to noise ratio is always lower.

And we know that Higher SNR ---> lower bit error rate.
lower SNR ---> higher bit error rate.

So why is a linear amplifier used in various communication systems and computing systems?

The signal must be amplified in order to be detected: The detector cannot detect a very weak signal, or the noise of the detector itself would degrade seriously the signal.
In addition, amplification performs also the function of saparate the useful signal from out-of-band signals (interference, out-of-band noise, etc).



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The amplifier must be linear to keep nonlinear and linear distorsions of amplified signal as low as necessary. The consequence of linear and nonlinear distortions is spoiled shape of signal and thus increased number of errors in transmission, worse BER.

I'm agree with previous responses by Zorro and Borber. Addind to their responses, transmition of information in digital or analog systems are in differential mode, noise appear in common mode and receivers amplify differential mode ans atenuate common mode, wich elevate SNR. Another techniques are FM and PWM to transmit information both are less affected by noise.

The main reason for using a linear amplifier is to match the level of the signal that you want to convert to digital, to the input of your DAC. The distortion that is produced during the digitization proccess comes from two sources the nonlinearity of the DAC and the quantization error. The quantization error depends on the input signal amplitude the larger the signal the smaller the quantization distortion. Of course you must calculate the maximum input signal so that the DAC will not clip.

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