Current reused Colpitts VCO and frequency divider for quadrature generation

Abstract-A 2.5 GHz low power current reused Colpitts VCO and divide-by-two circuit is proposed in 0.18μm CMOS technology. The divider is stacked on top of a common drain g_m-boosted differential Colpitts VCO to share the DC current. A parasitic capacitance neutralization technique is used to eliminate the miller effect with the VCO, and improves the generated negative resistance and phase noise performance. The circuit can provide a 2.36-2.53GHz quadrature output frequency, and consume 4mW at 1.8V supply voltage. The simulated output phase noise is -126dBc/Hz at 1 MHz offset frequency when the divider output is 2.45 GHz.