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A CMOS standard ring oscillators with 5 and 7 stages are examined in 0.35μm and 0.18μm technologies. For optimum number of ring oscillator stages (N = 5) the operating frequencies of 1.62 GHz and 3.07 GHz are obtained in 0.35μm and 0.18μm technologies, respectively. The 5-stage ring oscillator topology is further investigated while changing power supply and temperature. Their influence on oscillating frequency can be compensated by introducing additional voltage controlled cascade PMOS or/and NMOS transistors in one inverter stage. As ring oscillator is a part of UWB-IR (Ultra Wide Band Impulse Radio) pulse generator, its oscillating frequency determines the central frequency of the pulse spectrum and influence significantly spectrum fitting within UWB FCC mask.