An X-band CMOS low noise amplifier with a three-coupled transformer based <i>g</i><sub><i>m</i></sub>-boosting structure for phased array receivers

This letter presents a design strategy for a three-coupled transformer based gm-boosting structure, which optimizes low noise amplifier (LNA) performance with rapid iteration design of the three-coupled transformer. The proposed strategy is used in a wideband LNA for phased array receivers operating at X-band. The three-coupled transformer based gm-boosting structure is employed for gain and noise figure (NF) improvement, wideband input matching and a single-ended-to-differential conversion. Two CS stages are cascaded to provide higher gain and the inter-stage matching is implemented by two staggered transformers which extend the bandwidth (BW). The LNA achieves a measured gain of 21.5 dB and the −3-dB BW covers 7 to 14 GHz. The return loss is better than 10 dB across the BW. The measured NF is 3.0 dB at 7.5 GHz and the input third-order intercept points (IIP3) is −4.6 dBm at 14 GHz. The LNA occupies a core area of 0.21 mm2 implemented in 40-nm CMOS process.