A digitally controllable oscillator is provided with a variable-frequency ring oscillator comprising an odd number of inverting circuits connected to each other in a ring. The frequency of the output signal of the ring oscillator is determined by a digital input signal specifying the frequency of the...http://www.google.de/patents/US5331294?utm_source=gb-gplus-sharePatent US5331294 - Oscillation circuit including a ring oscillator having a changeable number of inverter circuits
