This paper describes a 5.8-GHz up-conversion mixer core based on a current-folded architecture and a 5-GHz differential emitter-coupled voltage-controlled oscillator (VCO) utilizing a center-tapped inductor and a substrate shield. Both circuits are fabricated in a 0.8-/spl mu/m 45-GHz f/sub T/ SiGe heterojunction bipolar transistor (HBT) technology. The supply voltage range is between -2.3 V and -3.3 V to meet the requirements of mobile circuits. Special care has been taken with the inductor model. A distributed modeling approach was used to generate an inductor model from a geometrical description. This type of model also has the advantage that it can simulate RF effects in both time and frequency domain.