High Quality, All-Digital RF Frequency Modulation Generation with the ADSP-2181 DSP and the AD9850 Direct Digital Synthesizer Application Note (AN-543)

FM modulators have been with us since the time of Major Edwin H. Armstrong (sometimes known as the father of FM) and his classic 1936 paper on the subject. He first put down on paper the fundamental concept of a fixed center frequency that is varied per a constant deviation ratio that is independent of the frequency of the modulating signal. FM became very popular because much of the noise generated in nature exhibits AM characteristics. The signal-to-noise ratio of an FM signal will be found to exceed that of an AM signal due to the improvement ratio related to the deviation ratio. We are all familiar with the wideband FM broadcast band and its superior sound quality and noise immunity when compared with AM broadcast.