The present invention relates to a ring oscillator including a plurality of cascaded inverting delay stages, each delay stage includes a differential pair of input transistors, a variable resistive load coupled to each transistor, a differential output between the variable resistive load and the corresponding input transistor, a variable current source coupled to the differential pair of transistors for variably setting a bias current through the differential pair of transistors, and an input coupled to the variable resistive load and the variable current source for receiving an configuration signal, wherein the variable resistive load and the variable current source are changed in response to the configuration signal, such that the bias current increases, while the variable resistive load decreases and vice versa.