Amplifier Stages

If you're looking for how linearity is maintained from one stage to another while achieving higher gains ...

Most bipolar op amps with 3 stages have each stage biased to operate in its linear region.
A amplifier can be horribly non linear, and produce a very linear output when you add feedback and have the open loop gain much larger than the feedback gain. Op-amp is a prime example.
There are a few ways that linearity can be maintained in an amplifier:
  1. Designing the amplifier circuit to operate in the linear region of its transfer characteristic: The transfer characteristic of an amplifier is a plot of the output signal versus the input signal. In the linear region, a small change in the input signal results in a proportional change in the output signal. By operating the amplifier in this region, the output signal will closely follow the input signal, without introducing any non-linearities.
  2. Using feedback in the amplifier circuit: Feedback is a technique in which a portion of the amplifier's output signal is fed back to the input. This can be used to cancel out any non-linearities introduced by the amplifier, resulting in a more linear transfer characteristic.
  3. Using a linearizing element in the amplifier circuit: Some amplifier circuits use additional elements, such as diodes or transistors, to linearize the transfer characteristic. These elements can be used to compensate for non-linearities introduced by other parts of the circuit.
Overall, maintaining linearity in an amplifier requires careful design and attention to the various factors that can introduce non-linearities in the circuit.