A CMOS relaxation oscillator which generates quadrature triangular and square waveforms is presented and fabricated in 0.18 μm CMOS. The proposed oscillator consists of cascaded two-stage charge-discharge full-differential circuits with sequential common-mode comparators based on cross-coupled connection. Experimental results show that the proposed oscillator generates quadrature-phase waveforms with less than 1% phase mismatch. The proposed oscillator also achieves a tuning range of more than 40% with digitally programmable timing capacitors and offers phase noise of -132 dBc/Hz at 1 MHz offset frequency.