Implementation of Perfect-Magnetic-Coupling Ultra-Low-Loss Transformer in Standard RFCMOS Technology

In this paper, 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 GHz 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 ultra-low-voltage high-performance transformer-feedback LNAs and VCOs, and other RF-ICs which include transformers.