Power amplifier linearity refers to the ability of a power amplifier to faithfully reproduce the input signal without introducing significant distortions or nonlinearities in the output signal. In an ideal world, a power amplifier would produce an output signal that is an amplified replica of the input signal, scaled by a constant factor (the amplification factor).
However, in real-world scenarios, power amplifiers can introduce nonlinearity due to various factors, such as limitations in the electronic components, circuit design, and the properties of the active devices used in the amplifier. Nonlinearity causes the output signal to deviate from the ideal amplified replica of the input signal, resulting in distortion.
Distortion in power amplifiers can manifest in several ways, such as harmonic distortion, intermodulation distortion, and amplitude compression. Harmonic distortion occurs when the amplifier generates harmonics of the original signal at frequencies that are multiples of the input signal frequency. Intermodulation distortion happens when the amplifier produces new frequencies that are the sum and difference of multiple input signal frequencies. Amplitude compression occurs when the output signal does not increase linearly with an increase in the input signal amplitude, limiting the amplifier's usable dynamic range.
In audio applications, for example, a high level of linearity in power amplifiers is crucial to maintain faithful sound reproduction and avoid introducing unwanted artifacts that can degrade audio quality.
To quantify the linearity of a power amplifier, engineers use various metrics, such as Total Harmonic Distortion (THD), Intermodulation Distortion (IMD), and the 1 dB compression point (P1dB). Lower THD and IMD values and a higher P1dB point indicate better linearity and performance in power amplifiers. Manufacturers often specify these parameters in the amplifier's datasheet to give users an idea of its linearity characteristics.