A CMOS resistive feedback differential low-noise amplifier with enhanced loop gain for digital TV tuner applications

A resistive feedback differential low-noise amplifier (LNA) with enhanced loop gain is implemented as a part of a digital TV (DTV) tuner using a 0.18-μm CMOS process. A voltage buffer having higher gain, higher linearity, and lower noise figure (NF) than those of the conventional differential source follower (DSF), which is called the differential hybrid voltage buffer (DHVB) in this paper, is designed by combining the common source amplifier and source follower. By adopting the DHVB with optimized performance as a voltage buffer of the conventional resistive feedback differential LNA, the loop gain of the LNA can be increased. This leads to a highly linear resistive feedback LNA with higher gain and lower NF compared to the conventional resistive feedback LNA. For the wide gain range, the proposed LNA includes the variable gain function based on the resistive attenuator employing the T-switch. The measurement results of the proposed LNA exhibit a maximum gain of 16 dB and a gain range of 50 dB. At maximum gain, the LNA shows an average NF of 2.8 dB, a third-order input-referred intercept point of -1 dBm, a second-order input-referred intercept point of 40 dBm, and S11 of under -9 dB in a frequency range from 48 to 860 MHz. The power consumption is 30.6 mW at a 1.8-V power supply and the chip area is 0.25 mm².