A Fully Integrated Variable-Gain Multi-tanh Low-Noise Amplifier for Tunable FM Radio Receiver Front-End

In this paper, we present a two-stage variable-gain low-noise amplifier (LNA) used in a frequency modulation (FM) radio receiver front-end for a variety of portable audio devices. We also describe a tunable antenna interface and a voltage regulator used in the front-end. The front-end can be tuned to resonate at FM frequencies from 63 to 129 MHz. The two-stage LNA achieves a programmable small-signal voltage gain from 0.5 to 32.5 dB in around 1-dB steps across the FM band from 76 to 108 MHz. Its input-referred noise voltage is less than 1.5 nV/radicHz in the high gain mode. Furthermore, the linearity of the LNA and front-end is improved by employing the multi-tanh design principle. In the low and high gain modes of the LNA, the measured IIP3 are -5.2 and -16.5 dBm, respectively, compared with -10.5 and -25.5 dBm without using the multi-tanh doublets. The whole LNA is fabricated in a TSMC 0.18-mum CMOS technology. It draws maximum 4.5 mA current (5.5 mA including the regulator) from a 1.35-V supply and occupies 0.15 mm
²
of chip area. Experimental and simulation results are both provided to demonstrate the performance of the LNA and front-end.