Abstract: A clock generating apparatus includes a crystal oscillator wherein a clock signal generated from the crystal oscillator passes through a band pass filter to become a reference clock signal of a sine wave. This clock signal is applied to a first multiplier and is delayed 1/4 cycle by a 1/4 cycle delayer to become a clock signal cos2.pi.f.sub.ct. The delayed signal is applied to a second multiplier. When an external horizontal synchronizing signal is externally applied, an A/D converter samples the horizontal synchronizing signal in response to a reference clock signal to apply a digital signal to an operating device. The operating device operates a phase difference between an absolute phase of the digital signal and a predetermined phase to output a sine wave component sin(a-b) and a cosine wave component cos(a-b) corresponding to the phase difference. The first multiplier multiplies the clock signal sin2.pi.f.sub.ct as a reference by the sine wave component sin(a-b).

Abstract: A modulation signal is digitally integrated by an integration circuit and then phase-modulated by a phase modulating circuit. The integrated modulation signal is converted in phase modulating circuit to first and second digital modulation signals having phases orthogonal to each other. A carrier signal from a carrier signal generating circuit is converted to first and second carrier signals having phases orthogonal to each other. The first digital modulation signal and the first carrier signal are multiplied in a D/A converter and the second digital modulation signal and the second carrier signal are multiplied in a D/A converter, which multiplications are output as analog signals. These two analog signals are added to an adder to obtain an FM modulation output. As the foregoing, an FM modulation is digitally performed to obtain a highly reliable FM modulator of an excellent linear characteristic without a higher distortion.