Power optimized LC VCO and mixer co-design

A capacitively source degenerated buffer provides a negative impedance and can be used as the negative resistance cell in the voltage-controlled oscillator (VCO). This eliminates the need for a negative resistance cell within the VCO itself. Eliminating the negative resistance cell within the VCO allows us to reduce the overall power consumption for a design that combines a VCO with a follow-on mixer stage. Further, as the VCO directly drives the mixer, the input capacitance of the mixer can be incorporated into the degeneration capacitor of the negative resistance cell. In other words, the mixer and VCO when co-designed can result in a significantly more optimal design. This paper presents the design for a prototype 4 GHz LC VCO and a mixer that has been designed for a 5 GHz RF and 1 GHz IF radio application in the 0.18 μm TSMC CMOS technology.