Nonlinear Distortion Analysis in the Frequency Demodulator Using Feedback

A general method for the accurate analysis of the response of a frequency demodulator using feedback (FMFB) to an arbitrary frequency modulated (FM) signal is developed. This approach is employed to determine the FMFB outputs for two specific modulating signals, Gaussian noise, and a single sine wave. The proposed method is then applied to three different FMFB configurations differing in their low-pass filter structure. As a result, generalized curves enabling easy evaluation of the intermodulation (IM) distortion and the harmonic distortion are obtained. When designing the FMFB on the basis of these results, the influence of the relevant system parameters, such as IF filter bandwidth, feedback factor, position of the channel in the baseband, structure of the low-pass filter, etc., on the nonlinear properties of the FMFB can be controlled, simply and in a straightforward manner. The accuracy of the method has been verified in those rare cases for which solutions are already known.