Abstract: A 3–5 GHz broadband flat gain differential low noise amplifier (LNA) is designed for the impulse radio ultra-wideband (IR-UWB) system. The gain-flatten technique is adopted in this UWB LNA. Serial and shunt peaking techniques are used to achieve broadband input matching and large gain-bandwidth product (GBW). Feedback networks are introduced to further extend the bandwidth and diminish the gain fluctuations. The prototype is fabricated in the SMIC 0.18 μm RF CMOS process. Measurement results show a 3-dB gain bandwidth of 2.4–5.5 GHz with a maximum power gain of 13.2 dB. The excellent gain flatness is achieved with 0.45 dB gain fluctuations across 3–5 GHz and the minimum noise figure (NF) is 3.2 dB over 2.5–5 GHz. This circuit also shows an excellent input matching characteristic with the measured S11 below –13 dB over 2.9–5.4 GHz. The input-referred 1-dB compression point (IP1dB) is –11.7 dBm at 5 GHz. The differential circuit consumes 9.6 mA current from a supply of 1.8 V.

Key words: LNA,  differential,  UWB,  flat gain,  feedback