Implementation of perfect-magnetic-coupling ultralow-loss transformer in RFCMOS technology

In this letter, we propose a single-turn multiple-layer interlaced stacked transformer structure with nearly perfect magnetic-coupling factor (k_IM∼1) using standard mixed-signal/RF CMOS (or BiCMOS) technology. A single-turn six-layer interlaced stacked transformer was implemented to demonstrate the proposed structure. Temperature dependence (from -25°C to 175°C) of the quality-factor (Q-factor), k_Im, resistive-coupling factor (k_Re), maximum available power gain (G_Amax), and minimum noise figure (NF_min) performances of the transformer are reported. State-of-the-art G_Amax of 0.762 and 0.904 (i.e., NF_min of 1.181 dB and 0.437 dB) have been achieved at 5.2 and 8 GHz, respectively, at room temperature, mainly due to the perfect magnetic-coupling factor and the high resistive-coupling factor. The present analysis is helpful for RF engineers to design ultralow-voltage high-performance transformer-feedback low-noise amplifiers and voltage-controlled oscillators, and other radio frequency integrated circuits which include transformers.