An ultra-low-power, start-up and phase noise performance improved 2-stage differential ring voltage-controlled oscillator (VCO) is proposed. The proposed delay cell architecture reduces power consumption by eliminating the cross-coupling latch of the conventional ring VCO. Instead of the latch, the inverters in the proposed delay cell produce negative conductance by insertion of an additional RC network, which improves the start-up performance of the proposed VCO. The proposed delay cell architecture also improves the phase noise performance of the VCO as it sharpens the drain current of the inverter stage such that it resembles an impulse waveform, which reduces the root-mean-square value of impulse sensitivity function. Implemented in a 65-nm CMOS technology, the measured phase noise of the proposed VCO at 1 MHz offset is -94.84 dBc/Hz at 490 MHz oscillation frequency while dissipating 45 mu W from a 0.6-V supply. The figure of merit is 162.1 dBc/Hz.