A UHF variable gain amplifier for direct-conversion DVB-H receivers

A CMOS fully differential UHF variable gain amplifier for use in a direct-conversion DVB-H receiver is presented employing input devices with variable aspect ratios. High linearity is achieved by reducing the transconductance of the input transistors for lower gain settings. It is shown that this technique has better linearity and noise performance compared to the conventional methods in which the gain reduction is performed at preceding stages. Implemented in TSMC 0.18-mum CMOS process, the inductorless RF VGA covers a voltage gain ranging from 15.5 dB to -6.5 dB with a maximum IIP3 of +24 dBm. The amplifier achieves a 3-dB bandwidth of 1.4 GHz and a minimum noise figure of 5.8 dB while drawing 3.6 mA from a 1.8 V supply.