a frequency modulator comprises an oscillator circuit , and a phase adder circuit receiving a signal derived by phase - shifting an oscillation output of the oscillator circuit by 90 ° and multiplying the phase - shifted signal by a modulating signal , and adding the product , thereby varying an oscillation frequency of the oscillator circuit . the frequency modulator is characterized in that the amplification elements of the phase adder circuit and the oscillator circuit are connected in parallel with respect to a power source .