A low-power, high-frequency, 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 constant 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 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 0.178, respectively. A figure of merit called a normalized carrier-to-noise ratio is 158.23 dBc/Hz at the 2 MHz offset from 2.83 GHz. Comparisons to other approaches are also presented.