In this paper, a low-power CMOS variable gain amplifier (VGA) with an approximated exponential equation is presented. The proposed VGA is composed of two cascaded variable gain stages and a fixed gain stage, and has advantages of low-power, wide controlled gain range and temperature independent. The VGA is implemented in 0.18um CMOS technology. The simulations show that a total linear gain range of 80dB (-15dB～65dB) with 3-dB bandwidth can be obtained at 50MHz; the IIP3 varies from -4dBm to -40dBm. The power dissipation is less than 2.2mA from a 1.8V supply voltage; the NF is only 14dB (at the 65dB gain). And the control circuit provides a gain error lower than ±1.5dB over the full temperature and gain ranges.
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