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I was going through a document on GMSK modulation where it is specified that it is immune to distortion from non linear amplifiers.Also it was mentioned that non linear amplifiers are more battery efficient.The exact lines are:-

"Non-linear amplifiers are more efficient in terms of the DC power input from the power rails that they convert into a radio frequency signal. This means that the power consumption for a given output is much less, and this results in lower levels of battery consumption; a very important factor for cell phones."

Can anyone explain this concept?

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  • \$\begingroup\$ ""Non-linear amplifiers are more efficient in terms of the DC power input from the power rails that they convert into a radio frequency signal" - why?" is the core of this question, isn't it? \$\endgroup\$
    – pjc50
    Sep 15, 2016 at 10:00
  • \$\begingroup\$ @pjc50, Yes thats right..This is what i need to understand \$\endgroup\$ Sep 15, 2016 at 10:07
  • \$\begingroup\$ In short, the same reason a linear voltage regulator is less efficient than a switching regulator... The power devices in a linear regulator/amplifier are always acting in the lossy region. Switching supplies and amplifiers take great pains to minimize the switching times, resulting in less operation of the power devices in the lossy linear reagion; they are ideally either on or off. \$\endgroup\$
    – R Drast
    Sep 15, 2016 at 11:12
  • \$\begingroup\$ electronics-tutorials.ws/amplifier/amplifier-classes.html \$\endgroup\$ Sep 15, 2016 at 18:45

2 Answers 2

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When you push a non-linear amplifier transistor to extreme non-linearity, it becomes a fast switch, whose on-off cycle period is 1/f (where f is the RF carrier frequency). A switch dissipates no power when OFF (where current is zero), and it dissipates no power when ON (where voltage across it is zero). This is also why PWM controllers are also highly efficient.
A transistor or FET wastes power when it conducts current while simultaneously having a voltage across its terminals. For a Class-A amplifier, this is the normal condition, 100% of the time.

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All amplifiers are nonlinear, there's no such thing as a "Linear Amplifier". You can operate an amplifier in a linear region, thus the shorthand. Some terms you should be looking for are Power Added Efficiency, Saturated Output, and Quiescent current.

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