Fine and wide frequency tuning digital controlled oscillators utilizing capacitance position sensitivity in distributed resonators

Recent advances have shown that all digital phase locked loops have several desirable advantages over its analog counterpart. One important element in the all digital phase locked loop is the digital controlled oscillator whose frequency resolution restricts the frequency resolution of the entire system. In this paper we propose a new structure for digital controlled oscillators utilizing the capacitance´s sensitivity dependence on position of the shorted transmission line to increase the frequency resolution. A 9 GHz transmission line based digital controlled oscillator was fabricated as a proof of concept. Measured results show that more than 100 times frequency step resolution increase is possible utilizing the same tuning capacitor size located at different points in the transmission line.