Analysis and Design of a Very Low Noise Oscillator in CMOS Technology

In this paper, a very low phase noise oscillator is proposed. Phase noise of the proposed VCO is lower than the lowest attainable phase noise of the conventional topologies. In the proposed circuit a fourth-order tank is employed, also the the current waveform injected the tank is class-C which provide the best DC to RF efficiency. Phase noise of the proposed oscillator has been theoretically investigated and closed-form formulae have been derived that shows the amount of phase noise improvement achieved by using the proposed circuit for different tank elements. 6 dB phase noise improvement in current-limited regime is achieved by using the proposed technique with same tank elements in comparison with the conventional topologies. In order to verify the derived formulae, the results of the calculations have been compared against simulation results. Their match are excellent.