Mathematical Modelling of the LC-Ladder and Capacitive Shunt-Shunt Feedback LNA Topology

In this paper a new low noise amplifier configuration is proposed to achieve wideband operation. This configuration consists of an LC-ladder filter and a common-emitter stage employing shunt-shunt capacitive feedback to realize wideband matching. Design equations for this configuration are derived, as well as equations for the important performance measures namely noise figure, gain and IIP3. The results of a design for achieving typical low noise amplifier specifications in the ultra-wideband are calculated from these equations and plotted. Without any optimization S11 of less than −10 dB over the entire frequency band and a minimum noise figure of 2.7 dB are predicted when achieving S21 of 20 dB. These results indicate that very good performance can be attained through the use of this technique. Simulations were also done to verify the calculated results.