Frequency modulation method

摘要

Method for frequency modulation of a digital carrier signal with a digital AF signal by means of a feedback phase accumulator and a carrier oscillator which generates the sample values of the modulated FM oscillation, characterised in that the modulation signal is sampled at the sampling rate fA/P where P > 1, in that, downstream or upstream of the feedback phase accumulator, the sampling rate is interpolated (increased) by the factor P by means of an inserted interpolation filter and the AF signal is filtered, in that the carrier oscillator which operates at the sampling rate fA generates a complex-value FM carrier signal, the carrier frequency of the unmodulated carrier at the modulation output side being fC = M . fA/P + f0 where M > 1 and f0 is an auxiliary frequency, and in that a band restriction is then carried out by means of a complex-value filter. Fully digitised frequency modulator with reduced levels of non-linear distortion following demodulation, capable of being integrated as a VLSI/ASIC component. Application generally in the field of frequency modulation and in particular in digital VHF broadcasting and for the transmission of the latter's signals via optical fibres. <IMAGE>