| 摘要 |
A method for FM modulation of a digital AF signal by means of a feedback-type phase accumulator and a carrier oscillator which generates the samples of the FM signal, characterised in that a complex-value FM intermediate-frequency signal is generated by the carrier oscillator which operates at a sampling rate fA = 1/T, the carrier frequency being fC = M . fA with the integral number M>1, in that this complex-value signal is then band-limited and interpolated by means of cascaded low-pass filters or complex interpolation filters, and in that a complex multiplication by e<j2 pi kf>0/<f>A takes place at an arbitrary point in the signal branch of the complex-valued signal for the final frequency shift, fA' being the sampling rate prevailing at the relevant point. Fully digitised frequency modulator with reduced nonlinear distortion after the demodulation, integrable as VLSI/ASIC chip, general application in the field of frequency modulation and especially in digital FM broadcasting and for transmitting its signals via optical fibre. <IMAGE> |
