Numerical Study on the Average Noise Factor of LNA for UWB Impulse Radio Systems

Noise factor (NF) is used to quantify the degradation of the signal passing through RF circuits. The spot NF widely used in narrow band low-noise amplifier (LNA) is frequency dependent. It´s necessary to redefine the NF for the wideband LNA where the ultra-wideband (UWB) signal pulse is assumed to be of the Gaussian pulse. The average NF suitable for the wideband LNA is discussed firstly. Numerical study on the average NF of LNA for UWB impulse radio is presented in this paper. The average NF is analyzed to quantify the relationship between LNA and Gaussian pulse. A design strategy is suggested that the Gaussian pulse frequency response is optimized to lower average NF. The average NF is equivalent to the spot NF when narrow band assumption is made. For wideband systems with constant frequency response, the average NF is determined by two endpoints frequency summation