The feedback technology for gain flatness and stability of UWB LNA

摘要

In this paper, based on small signal models of hetero-junction bipolar transistors (HBTs) with different feedback circuits, the expressions for S parameters of the device are derived to analyze the influence of different feedback technologies on amplifier performance, especially on the stability and the gain flatness of Ultra-Wideband Low Noise Amplifier(UWB LNA). When a serial inductor or a parallel capacitor is added into the feedback circuits to induce reactive feedback, the amplitude of S21 increases as the frequency increases, the HBT's gain inherent decreasing at high frequency is compensated, a good stability performance can also be reached simultaneously. Based on reactive feedback techniques, we design a 3GHz–10GHz UWB LNA. The simulation results show that throughout the whole frequency band, the amplifier remains unconditionally stable, has a high transmission gain, good gain flatness and low noise figure.