A Digitally Controlled Variable-Gain Low-Noise Amplifier With Strong Immunity to Interferers

A variable-gain low-noise amplifier with capacitive step attenuators is presented. In order to improve linearity at medium gains settings, digital gain control is performed using a current-splitting technique at the cascode transistors. The fabricated LNA shows an IIP3 increase with constant OIP3, from -1.1 dBm at 25.8 dB gain to 3.5 dBm at 21.2 dB gain. Using capacitive attenuator control, a wide gain range of over 42.7 dB is achieved. Using a 0.5-mum BiCMOS process, the proposed LNA shows an NF of 1.5 dB at 650 MHz and a power consumption of 15.4 mW under 2.9 V supply voltage. The fabricated tuner-IC, including the proposed LNA, satisfies all requirements pertinent to DVB-H reception, with sufficient margins for practical integration. Under typical DVB-H reception scenarios involving strong interferers, measurement results and analytical calculations showed good consistency at various gain settings.