Analysis of $\hbox {IM}_{\rm 3}$ Asymmetry in MOSFET Small-Signal Amplifiers

This paper describes and analyzes asymmetry issues for weakly nonlinear MOSFET Common-Gate (CG) and Common-Source (CS) architectures. Using a Volterra series analysis, the cause of asymmetry in CG and CS amplifiers is explained. The asymmetry between high-side and low-side products in the CG amplifier exhibits a larger amplitude difference at low-frequency offset than at high frequency offset, while the CS amplifier shows more asymmetry at a high frequency offset. The magnitude of the product asymmetry in the CS amplifier can be significantly higher than the CG amplifier. Methods of mitigating asymmetry are suggested for both CG and CS amplifiers. A 65 nm Si CMOS technology is used for the simulation verification of the results derived in this paper.