A wideband CMOS variable-gain low noise amplifier with novel attenuator

This paper presents a wideband variable-gain low noise amplifier (VGLNA) which is used in mobile TV tuner covering VHF band (50 to 250 MHz) and UHF band (470 to 860MHz). The proposed VGLNA includes three gain paths for different input signal strengths: high gain path, attenuation path, medium gain path. The high gain path is realized by an active AC feedback LNA, whose DC current is set by a constant-G_m biasing; the novel attenuator used in attenuation path has constant input impedance which guarantees a good S11 with the variety of gain; the medium gain path is the combination of one active AC feedback LNA and one attenuator. The chip is implemented in 0.18 μm CMOS process and achieves a gain range over 42 dB (2dB/step), a minimum noise figure of 2 dB at maximum gain, an IIP3 of 27.9 dBm at minimum gain. The die consumes 8 mA from 1.8 V supply voltage at maximum gain.