Highly Linear Wideband Low-Noise Amplifiers for Sub-6 GHz Using Cascode and Diode-Connected Postdistortion Circuits

This article presents two types of postdistortion (PD) circuits—diode-connected PD (DCPD) and cascode PD (CPD)—positioned subsequent to low noise amplifiers (LNAs) operating in the 2.2–5-GHz frequency range. Each LNA with PD design, performance, and comparison is based on a core two-stage cascode topology, using identical transistor dimensions and bias voltages. The purpose of this study was to compare the linearity performance and linearity bandwidth of DCPD and CPD and achieve optimum performance in gain, noise figure (NF), bandwidth, and linearity simultaneously. The auxiliary circuits were designed to cancel third-order nonlinearities, thereby improving the third-order input intercept point (IIP3). Both LNAs achieved a gain of 30.5 dB, an NF of 0.85 dB, and an output power of 14 dBm at 1-dB compression at a center frequency of 3.5 GHz with a power consumption of 240 mW. The auxiliary circuits used in the LNA design showed varying IIP3 based on the type of PD circuit employed. The CPD circuit demonstrated a linearity improvement at the center frequency, achieving an IIP3 of 1.5 dBm. On the other hand, the DCPD circuit delivers an IIP3 of 10 dBm, one of the highest values reported in current state-of-the-art designs. In addition, a low-power mode of operation is measured with a power consumption of 68 mW for both LNAs. In this mode, the CPD circuit achieves an IIP3 of 5 dBm at 4.5 GHz, while the DCPD circuit demonstrates an IIP3 of 3 dBm across the 4–4.5-GHz range.