A Wideband CMOS LNA Using Transformer-Based Input Matching and Pole-Tuning Technique

A wideband low-noise amplifier (LNA) featuring transformer-based wideband input matching is proposed for millimeter-wave applications. By analyzing the properties of conventional series input matching networks, which were widely employed in narrowband LNAs and shunt-series matching networks for bandwidth extension, a novel input matching network possessing the merits of both was proposed. For further bandwidth extension, another peak of input impedance at a higher frequency is introduced for the proposed input matching network. Moreover, it is proved that the proposed input matching network can suppress the gate resistor noise, resulting in significant noise figure (NF) improvement of an LNA. On the other hand, the NF is further reduced by connecting a transformer between the two amplification stages, which helps suppress the noise contribution from the second stage, leading to an LNA design with NF lower than 4.5 dB over a very wide operating bandwidth. To enhance the gain bandwidth, the peak distribution, including both shunt peaking and series peaking, is discussed. By appropriately distributing these peaks, which is also known as the pole-tuning technique, a wider gain bandwidth can be obtained. To validate the proposed techniques, an LNA with two common-source (CS) stages is designed and fabricated using a 65-nm CMOS process, and the overall chip size, including all pads, is only 0.26 mm
²
. The two CS stages are cascoded for dc biasing to reduce the power consumption. Experimental results show that a peak gain of 13.5 dB is achieved within a -3-dB bandwidth from 19.2 to 42.6 GHz. The measured NF is 3.1-4.5 dB, and the input 1-dB gain compression point (IP
_{1 dB}
) ranges from -13.54 to -9.89 dBm in the entire gain bandwidth. The input return loss S
₁₁
is less than -10 dB over a frequency range of 16.8-38.9 GHz. Moreover, benefiting from the current-reuse technique, the power consumption of the LNA is only 6.36 mW.