New noise cancellation topology in common-gate LNAs

In this paper a new approach for designing noise canceling common gate (CG) low noise amplifiers (LNAs) is proposed. This method investigates using inductively degenerated common source (IDCS) stage in parallel with CG stage instead of common source (CS) stage. Considering special specification of IDCS LNA, proposed topology can achieve lower noise figure (NF) and better input impedance matching. Analytical calculation for this topology is performed and the equations to satisfy input impedance matching along with noise cancellation condition are presented. The NF of proposed LNA is also calculated while satisfying these conditions by using the calculation of each noise source's transfer function. To validate theoretical analysis, two different LNAs in X band are designed and optimized. The simulations are performed using Advanced Design System (ADS) electromagnetic momentum with GaAS pHEMT 0.1 μm process model. The results shows the proposed method can achieve better input impedance matching and lower NF while the output impedance matching and gain have relatively the same behavior.