A CMOS active feedback balun-LNA with high IIP2 for wideband digital TV receivers

A wideband active feedback single-to-differential (S-to-D) low-noise amplifier (LNA) for digital TV (DTV) tuners composed of a S-to-D converter, a voltage combiner, and a negative feedback network is proposed to achieve low noise as well as to improve the linearity performances (IIP2 and IIP3) simultaneously. By feeding the single-ended output of the voltage combiner, which is used for combining the differential output of the S-to-D converter, to the input of the LNA through the feedback network, a wideband S-to-D LNA exploiting negative feedback is implemented. The differential mode operation of the voltage combiner reduces the second-order nonlinearity feedback, allowing us to improve both the IIP3 and IIP2 of the LNA at the same time. Two LNA design examples are presented to demonstrate usefulness of the proposed approach. The LNA I, by adopting a common source (CS) amplifier with a common gate, common source (CGCS) balun load as the S-to-D converter, is able to achieve a high gain and a low noise figure (NF) by increasing the loop gain. The LNA II using the differential amplifier with the ac-grounded second input terminal is designed for robust IIP2 to PVT variations.