A high dynamic range CMOS variable gain amplifier for mobile DTV tuner

A high dynamic range RF variable gain amplifier (RFVGA) suitable for mobile digital television (DTV) tuners is presented. Variable gain is achieved using a capacitive attenuator and current-steering transconductance (G(m)) stages, which provide high linearity with relatively low power consumption. A novel broadband input impedance matching scheme based on resistive shunt-feedback is proposed. This scheme allows the RFVGA to achieve a low noise figure. A gain control technique suitable for CMOS current-steering variable gain amplifiers is described; it features 1 dB per step resolution, independent of process and temperature variations. The chip is fabricated in six-metal 0.18 mu m CMOS technology and consumes 12.2 mA current from 1.8 V supply. The RFVGA achieves 16 dB maximum gain, 33 dB gain control range, a 4.3 dB noise figure, and an IIP3 higher than 25 dBm.