I have to ask this -- if I was amplifying an audio signal or signal for wireless communication, would such an amplifier be linear by design.
Somehow, I tend to base my concept of amplifier using an audio signal.

Ummm...yeah, audio amplifiers are usually linear, give or take a few percent, depending on how much power you are delivering. Wireless communication used to be linear, but it's mostly digital now. Compare AM radio to 256-QAM. I believe we have established as fact that you can not run a signal through an ADC converter, change some ones and zeros, run it through a DAC converter, and call it, "amplified". That will only give you a bunch of ones and zeroes at the same amplitude as the power supply voltage of the DAC chip, therefore, amplification is an analog process.

Let me widen your view. A lot of analog design is about interfacing to the physical world. Anything that can be measured can be amplified. I have amplified signals from a parts per billion oxygen sensor. Compared to that, a microphone or an infrared remote control is easy! If I can get a few dozen nanoamps up to a level that drives a digital display, I can get it to control kilowatts of power. You can get a digital signal to control kilowatts, too, but the instant you step out of 3.3 volts or 5 volts, you need amplification. That amplification can be from way below 5 volts to get the signal large enough to run a digital input, or it can take the output of a digital chip and control some massive power. From my point of view, the whole digital world is almost a single power level, except for maybe a Class D power amplifier. All the other power levels are analog.

 

I have to ask this -- if I was amplifying an audio signal or signal for wireless communication, would such an amplifier be linear by design.

Not necessarily. It depends on what the objective is.

Somehow, I tend to base my concept of amplifier using an audio signal. When I think about it, the audio sound from an amplifier would sound funny if part of input were amplified to one level and part amplified to another level.

Remember I mentioned companding? Well, that is used extensively in audio systems. Look it up.

 

[quoteI have to ask this -- if I was amplifying an audio signal or signal for wireless communication, would such an amplifier be linear by design.
Somehow, I tend to base my concept of amplifier using an audio signal. When I think about it, the audio sound from an amplifier would sound funny if part of input were amplified to one level and part amplified to another level.[/quote]

We keep saying "It depends"

and that is true here too both for audio and for wireless comms amplifiers.

Wireless comms amplifiers are often non linear simply because it is more power efficient that way.

Audio amplifiers are non linear for a variety of reasons, some very complicated like the Dolby system, the most obvious being the tone controls on your amp.
Since the response of the human ear to audio is non linear some amps have a so called loudness control, tailored to counter this.

since you are a digital buff, the most recent hearing aids store digital models of the wearer's ear and tailor the aid's response excatly to this, resulting in clearer hearing.

 

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Audio amplifiers are non linear for a variety of reasons, some very complicated like the Dolby system, the most obvious being the tone controls on your amp.
Since the response of the human ear to audio is non linear some amps have a so called loudness control, tailored to counter this.
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An amplifier gain change with frequency, such as from tone controls or a loudness control, do not make the amp non-linear.