This paper presents an on/off switched wideband three-stage voltage controlled ring oscillator for multiband ultra-wideband (UWB) systems. The ring oscillator is a part of UWB pulse generator, thus its oscillating frequency determines the central frequency of the pulse spectrum and has significant effect on spectrum fitting within UWB FCC mask. The oscillator has two control inputs, one for band switching and one for continuous control of the output frequency. The circuit was designed using ST 65nm CMOS process. Simulated data shows a very wide tuning range, approximately from 2.5GHz to 7GHz that the designed oscillator is suitable for ultra-wideband system applications. The phase noises at 1MHz and 10MHz offset are -89.2 dBc/Hz and -113.4 dBc/Hz, respectively.