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[摘要]：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 voltage-current 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 2 omega and Delta omega. 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-mu m 1P 6M CMOS process. Measurement results show a 9-dB output third-order intercept point improvement at an output power of -3 dBm. |
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