The paper describes how asynchronons delta sigma modulation can be used to generate frequency modulation. Present FM modulators have an inherent nonlinearity in the voltage/frequency characteristic, and as a consequence they are restricted to small percentage frequency deviations. The ADSM-FM modulator is inherently linear, allowing a wide percentage frequency deviation to be obtained. When incorporating this ADSM-FM modulator in the design of an FM broadcast exciter a system results which has an order of magnitude improvement in both signal/noise ratio and harmonic distortion compared with conventional designs.