A Design of 9kHz-0.5GHz Low Noise Amplifier with High Gain and Smooth Flatness

An ultra-wide band (UWB) low noise amplifier (LNA) of bandwidth 9 kHz-0.5 GHz, gain more than 30 dB, flatness fluctuating in ±0.8 dB, noise-figure less than 3 dB and the input and output reflection coefficient is less than -12dB within the range of the bandwidth is designed and measured. This LNA utilizes parallel negative-feedback between the base electrode and the collector electrode with an inductance in series with a resistance to compensate the decrease of the high frequency gain. In addition, an inductance in series with capacitance (LC) circuit is used as the signal coupling path at the input of the amplifier and a π-type attenuation network is used at the output port to improve the return loss respectively at the input and output ends of the amplifier. Compared with the traditional negative feedback amplifier circuit, the above improvement measures can improve gain-flatness and expand bandwidth obviously. Furthermore, this design adopt two stage cascade technology to achieve high gain and low noise figure. Simulation and measurement results are in excellent agreement.