A High-linearity, 80-dB CMOS VGA with DC-offset Cancellation for DAB Application

A three-stage cascaded variable gain amplifier (VGA) with continuous exponential voltage tuning characteristics in 0.18mum 3.3 V UMC process is presented for COFDM-based DAB/DVB system. The novel methods to improve the linearity of this circuit and to automatically cancel DC-offset are introduced. The operation frequency is only 38.912 MHz, but the circuit maintains 3dB-bandwidth wider than 70 MHz throughout its gain range as wide as 80 dB. It provides nearly 2.7dB/10mV slope in 0.3 V control voltage range, which leads to fast settling-time and high accuracy for AGC loop. At the worst case, the THD of the VGA is -50dB low, the IIP3 is about -4dBm; the simulated equivalent input density of white noise is 7nV/radicHZ. The overall current consumption is only 4 mA