Baseband Modeling and Distortion Equalization of FM Discriminators by Functional Methods

The output of a real discriminator is a nonlinear functional of the instantaneous frequency of its input signal. This functional may be separated into a linear term (the only significant term as the FM deviation goes to zero) and a distortion term. To remove the distortion, a feedback arrangement is proposed in which, after a subtraction, the discriminator output is passed through the inverse of the linear functional to obtain the desired output. The latter is fed to a circuit representing the distortion functional (to obtain what must be subtracted in the manner just described).