A common-gate common-source low noise amplifier based RF front end with selective input impedance matching for blocker-resilient receivers

Abstract

This paper presents an integrated wideband radio frequency front end with improved blocker resilience achieved through selective voltage attenuation at both input and output nodes of the low noise amplifier (LNA). The architecture differs from traditional LNA architectures where blockers are only attenuated at LNA output node. The proposed dual attenuation is attained by designing a low intrinsic input impedance common-gate common-source LNA with capacitive feedback, together with an N-path filtering load. The capacitive feedback across the LNA ensures that the selective N-path filtering profile at the LNA output is transferred to the LNA input nodes creating a selective input impedance. Consequently, the achieved front-end input impedance is low at blocker frequencies and matched to the source impedance at the desired frequencies, creating the desired voltage attenuation for blockers. Further, a detailed theoretical analysis of proposed architecture is presented, which leads to clear design guidelines. Evaluated in a 28-nm fully depleted silicon-on-insulator complementary metal oxide semiconductor (CMOS) process, front end is designed for wideband operation from 0.7 to 2.7 GHz. It consumes 11-mA current from a 1-V supply (excluding local oscillator (LO) buffering) and possesses a maximum noise figure of 5.1 dB. The front end demonstrates an out-of-band blocker compression point of -1.5 dBm and out-of-band IIP3 of +14 dBm at a 100-MHz offset from LO frequency. In comparison with a traditional common-gate common-source LNA-based front end with wideband input impedance matching, the proposed front end achieves 3.5-dB improvement in the blocker compression point at a 100-MHz offset from LO.