A cascode ultra-wideband (UWB) low noise amplifier (LNA) with a transformer for input matching was implemented in 45 nm SOI CMOS technology. The transformer is applied with high coupling (k = 0.7 to 0.8) for acquiring a stable wide band input impedance and so that a flat gain, return loss, noise figure, etc. in the whole UWB band is provided. The LNA affords a maximal power gain (S 21 ) of 12.5dB and a -3dB bandwidth of 10GHz from 2.8GHz to 12.8 GHz. It possesses low noise (NF min = 2.9dB) and a high 1 dB input compression point (IP1dB is -6dBm to 2dBm). The LNA occupies a small chip area of 0.14mm 2 without bond pads and consumes 11.7 mW from a 1V supply.