Balanced CMOS LC-tank analog frequency dividers for quadrature LO generation

A regenerative circuit based on an LC-tank balanced divider is proposed in this paper for quadrature LO signal generation. For given tank quality factor, it provides larger operation bandwidth and improved quadrature accuracy when compared with conventional injection locked frequency dividers. The operation bandwidth can be adjusted dynamically simply regulating the biasing current. Experimental results, carried on 0.18 /spl mu/m CMOS prototypes, show 42% range with a tank quality factor of 13.5 while driving 1.5pF output capacitance. At the band edge, biasing current is 8mA. Quadrature accuracy has been verified through the achievable image rejection of a purposely developed single side band up-converter. Measurements, performed on five samples, show a minimum image rejection of 44dB.