A high-frequency low-power sinusoidal quadrature oscillator is presented through the use of only current mirrors where the small-signal paths are realized through all NMOS transistors. The technique is relatively simple based on (i) inherent time constants of current mirrors, i.e. the internal capacitances and the transconductance of a diode-connected NMOS, (ii) a negative resistance formed by a transconductance of a diode-connected NMOS load of a current mirror. No external passive components are required. As a particular example, a 2.83-GHz, 0.374-fT, 0.38-mW sinusoidal quadrature oscillator is demonstrated. Total harmonic distortions (THD) are less than 0.8 %. The oscillation frequency is current-tunable over a range of 640 MHz or 22.62 %. The amplitude matching and the quadrature phase matching are better than 0.04 dB and 0.17°, respectively. A figure of merit called CNRnorm is 158.23 dBc/Hz at the 2 MHz offset from 2.83 GHz.