In an ideal world, the output of a power amplifier (PA) would be an identical scaled version of the input and most of the power consumed by the amplifier would reside in the output signal. Hence, we would have maximum efficiency and no distortion. In the real world, though, we fall short—real linear amplifiers tend to have very poor efficiencies.
Amplifiers used in cable distribution systems, for example, have excellent linearity, but this comes at the cost of efficiency. In most cases, the efficiency struggles to achieve greater than 6% with the balance of the power (94%) being wasted, which imposes economic, environmental, and application costs. In cellular base stations, electricity accounts for over 50% of the operating-expense (OPEX) costs.