Optimization of active feedback linearized amplifiers for multicarrier applications

A linearized amplifier is generally designed with the goal of reducing the two-tone intermodulation. In multicarrier systems, the signal entering a broadband amplifier is quite different from the superposition of two tones. It is much more similar to a Gaussian distributed noise and then, the goal must be to reduce the intermodulation produced in the presence of this kind of signals. In this paper, a formula for determining the signal to intermodulation ratio for gaussian inputs from the response to a single tone is obtained based on the theory of the Random Input Describing Function. Then, a new criterium for the design of linearized ampliflers is proposed. It is also shown that minimizing this S/I ratio is not equivalent to optimize the two-tones intermodulation due to the different behaviour of the signals in the time domain.