To extend a frequency range and to cover process, voltage and temperature (PVT) variation, a voltage controlled oscillator usually requires a large gain. The large gain, however, may cause more noise and supply pushing (due to increased sensitivity to the variation of a supply voltage). To solve this problem, one solution provides a set of sub-bands each having smaller gains compared to the voltage controlled oscillator for preventing the noise and supply pushing issues; a disadvantage of this solution, however, is that this technique requires digital calibration that results in greater manufacturing costs. Another type of voltage controlled oscillator with linear input voltage characteristics may have smaller gain and does not use digital calibration; a disadvantage of this solution, however, is that the linear range of this type of voltage controlled oscillator may not cover the full input range.