sizing of the cmos vco
The following indications can be used for the sizing of the oscillator:
• A reduced C leads to a high dependency of the parasitic capacitances;
• For a high C we have a higher current consumption;
• A reduced L leads to a high Gm which implies that a reduced resistance is
necessary to maintain the power dissipation;
• A high L implies a reduced C which means that the tuning frequency
diminishes,
• The power dissipation increases with the increase of the oscillation frequency;
• A Gm*Rp>1 is necessary for the start of the oscillation;
• The output amplitude is determined by the polarization current Vout=I*Rp or by
the entering of the transistors in the triode or cut-off regions, Vout=Vdssat
• To minimize phase noise, the oscillation amplitude should be maximized,
• The phase noise at a determined deviation frequency improves the tank’s Q
and the carrier’s power increases,
• The noise is inversely proportional to the square of the deviation frequency.