Design of bandpass low-noise amplifier with good selectivity and stopband rejection

In this work, a highly-selective bandpass low-noise amplifier (LNA) is proposed so as to achieve high gain, low noise, and good selectivity at the same time. As a result, the band selection filter usually connected with the LNA in a RF front-end may no longer be required. This effectively reduces the circuit size and cost of RF front-end circuitry. The proposed bandpass LNA is achieved by implementing the input and output matching networks of a two stage LNA with 2nd-order bandpass filters. In this way, the design of bandpass LNA can be easily achieved by incorporating the microwave filter synthesis technique into the conventional LNA design procedure. Specifically, a proposed bandpass LNA centered at 2.4 GHz with 200 MHz bandwidth is implemented using packaged HEMT on PCB. The measured in-band small signal gain is within 25.2±0.7 dB, and the in-band return losses are better than 11.6 dB. The measured in-band noise figure is better than 1.74 dB, with a minimum noise figure of 1.46 dB at 2.45 GHz. Notably, the proposed bandpass LNA achieves 39.5-dBc stopband rejection from DC to 1.81 GHz and from 3.12 to 20 GHz. The measured power dissipation is 21 mW and the input P1dB is -18 dBm.