Design of a UWB Interference-Rejection LNA Based on a Q-Enhanced Notch Filter

A Q-enhanced notch filter for interference-rejection LNAs is proposed in this brief. The active capacitance is introduced into the notch filter to improve the quality factor by the negative resistance effect. The designed notch filter achieves excellent performance with a narrow attenuation bandwidth from 5.75 GHz to 5.95 GHz, which can be applied to suppress interference from the IEEE 802.11a. To validate the feasibility of the proposed trap filter in both GaAs process technology and principle, a 3-15 GHz ultra-wideband low-noise amplifier was designed and fabricated using a 0.15-micron gallium arsenide pseudomorphs field-effect transistor process. The frequency-dependent feedback loops are employed between gate and drain stages for wideband input matching and gain flatness. The notch filter is inserted between two stages of the LNA. The measurement results show that the interference-rejection LNA achieves a maximum gain of 24.5 dB and a minimum noise figure of 1.8 dB in the operating band. The notch filter has a maximum interference-rejection ratio of 35.2 dB at 5.8 GHz with almost no effect on the desired gain of the LNA. The LNA has a power consumption of 168 mW, including the notch filter with a size of 1.93 × 0.72 mm².