A common-gate amplifier with transconductance nonlinearity cancellation and its high-frequency analysis using the volterra series

A common-gate (CG) amplifier employing a transconductance nonlinearity cancellation technique is designed for transmitter circuitry. The major contributor to the third-order nonlinearity in the CG amplifier is the second derivative of the transconductor ( g"_m which is the same case with a common-source (CS) amplifier. The multiple gated transistor (MGTR) technique, which was developed in the CS amplifier for transconductor nonlinearity cancellation, is applied to a CG amplifier. However, in the CG amplifier, the input driving impedance of a CG amplifier comprises a voltagecurrent feedback loop. Thus, a second-order interaction with feedback components generates a third-order distortion that limits input-referred third-order intercept point (IIP3) enhancement. This feedback influence on IIP3 can be relaxed by eliminating harmonic feedback components. Based on high-frequency analysis on a CG amplifier using the Volterra series, an RF current source is proposed to replace the conventional current source in the CG amplifier to eliminate harmonic feedback components at 2Ω and ΔΩ. By adapting the CG MGTR technique combined with the RF current source, a 2.4-GHz driver amplifier for Wibro/Wimax applications was implemented using a 0.18-μm 1P 6M CMOS process. Measurement results show a 9-dB output third-order intercept point improvement at an output power of -3 dBm.