Current reused Colpitts VCO and frequency divider with quadrature outputs

Abstract

A low power current reused Colpitts VCO and divide-bytwo circuit is proposed in 0.18 μm CMOS technology. The divider is stacked on top of a common drain g m -boosted differential Colpitts VCO to share DC current. A capacitance neutralization technique is used to compensate the miller effect of the parasitic gate-drain capacitance C gd in the VCO, and improves the generated negative resistance and phase noise performance. The Colpitts VCO works at 4.293-4.513 GHz, and can provide 2.147-2.257 GHz quadrature outputs through the stacked divide-by-two circuit. The VCO circuit exclude the output buffer consumes 2.8 mA at 1.8 V supply voltage. The measured phase noise is −109 dBc/Hz at 1 MHz offset frequency when the VCO output is 4.513 GHz.

A Comparative Study of Ring VCO and LC-VCO: Design, Performance Analysis, and Future Trends

“…A divide-by-two circuit with a current-reused VCO produces a quadrature output frequency. Phase noise performance and power consumption are balanced by stacking the divide-by-two circuit onto a g m -boosted Colpitts VCO with gate-to-source feedback and using parasitic capacitance neutralisation [221].…”