Frequency modulation method and frequency modulated signal transmitter

Abstract

A frequency-modulated signal transmitter and frequency modulation method are provided wherewith the linearity of an FM modulated signal is secured even when the level of frequency modulation after FM modulation is low. A level-subtraction circuit 24 is provided between a speech processing circuit 20 and a frequency modulator circuit 22 for subtracting the signal level of the speech-processed signal D2 from the speech processing circuit. The level-subtraction circuit comprises a level-subtraction stage 28, to which the speech-processed signal is input, that outputs a level-subtracted voice signal to the FM modulator circuit, and an average FM noise level setting stage 26 for setting the average level (±Esn) of the FM noise generated in the frequency modulator circuit and outputting that average FM noise level (±Esn) to the level-subtraction stage. In the level-subtraction stage, a signal in which the signal D2 and the average FM noise level (±Esn) have been added is obtained as a level-regulated voice signal, which level-regulated voice signal is sent as the modulating signal to the FM modulator circuit. The level subtraction may be implemented by either analog or digital processing.

Dependencies are inferred from the claim text.