METHOD OF AND APPARATUS FOR CONTROLLING MODULATION OF DIGITAL SIGNALS IN FREQUENCY-MODULATED TRANSMISSIONS

摘要

A programmable apparatus for generating a frequency modulated signal at a selected center frequency in accordance with digital data with at least first and second data levels. A modulator (331) is responsive to an input modulation signal for generating the frequency modulated signal at a frequency dependent on a quiescent voltage appearing at its input. A circuit (380) is provided for sampling and storing a value of the quiescent voltage. An addressable memory (301) stores a plurality of offsets. A programmable adding circuit (345) adds a downloaded offset voltage to the stored value of the quiescent voltage to output a high modulation voltage. A programmable subtracting circuit (349) subtracts a downloaded offset voltage from the stored value of the quiescent voltage to provide a low modulation voltage. An addressing circuit addresses the memory in accordance with a data transmission parameter for downloading a corresponding offset to the adding and subtracting circuits. A switch or multiplexor (346) is coupled to the subtracting and adding circuits for generating and applying to the modulator input an input modulation signal.