This paper proposes an RF signal generator using a time domain harmonic suppression technique based on Fourier series analysis. The circuit consists of four differential ring voltage control oscillators (VCO's) with phase differences and the pulse signal summing circuit. By summing pulse signals from VCO's with appropriate phase differences determined by Fourier series in time domain, the third and fifth harmonics can be cancelled without filters. To confirm the validity, a prototypal RF signal generator was fabricated in 90-nm CMOS technology. As a result, we succeeded in generating an RF signal from digital pulse signals. The frequency range is from 1.1 to 3.7GHz with 1-V power supply. The suppression of both the third and fifth harmonics are below -48dBc at 1.1GHz and -42dBc at 3.7GHz.