A 2.4-GHz CMOS resistively degenerated differential amplifier linearized using source coupled auxiliary FET pair

Abstract

A resistively degenerated differential amplifier is linearized by using a source-coupled auxiliary FET pair. The structure does not lower the effective g3 of the degenerated auxiliary FET pair while it efficiently cancels the second harmonic feedback component. Realized in 0.18-mum CMOS, the proposed differential amplifier achieves 9.8 dB of power gain, +7.7 dBm of output P1dB, and +25.8 dBm of peak OIP3. The maximum output power level with OIP3 greater than +20 dBm is extended by 7 ~ 10 dB compared to the conventional structure adopting a source-decoupled auxiliary FET pair. The results prove that the proposed degeneration configuration is suitable for linearizing a resistively degenerated CMOS differential amplifier.