A clock generation circuit is provided for improving the accuracy of a low power oscillator circuit contained therein. The clock generation circuit includes a crystal-less oscillator having at least two distinct frequency modes, including a low frequency mode and a high frequency mode. In some cases, the crystal-less oscillator may be adapted to generate a first clock frequency with relatively high accuracy and a second clock frequency with relatively low accuracy. A calibration and control circuit is included within the clock generation circuit for increasing the accuracy of the second clock frequency. In particular, the calibration and control circuit increases accuracy by using the first clock frequency to calibrate the second clock frequency generated by the same crystal-less oscillator. A system comprising the clock generation circuit and methods for operating a crystal-less oscillator having at least two distinct frequency modes are also provided herein.