A CMOS voltage controlled ring oscillator based on N-stage single-ended chain of different inverter types is described in this paper. The proposal is characterized by increased frequency stability (delta f over f larger than 2%) in term of power supply voltage variations in respect to standard solutions (delta f over f larger than 4%). The presented results are obtained using HSpice simulation and CMOS library model, level 49, for 1.2 µm technology.