Zero-IF VGA with novel offset cancellation

Reliable offset control is a vital feature of a zero-IF variable gain amplifier (VGA). Many traditional methods sacrifice speed (settling time) to achieve offset control by realizing a high pass feature in the signal path. This paper introduces a novel VGA architecture that is capable of controlling offset for all gain settings with a single offline calibration cycle. The VGA realizes very fast gain/startup settling time with only a slight increase in power and area requirements by eliminating the need for a high pass filter. The VGA circuit draws 3mA and has a gain range of 0/spl sim/42dB with 1dB steps. It has a 10MHz bandwidth at 42dB, has a gain settling time of 140nsec, and controls output offset within 2.2mV.