Two variable gain amplifiers (VGAs) that adopt new approximated exponential equations are proposed in this paper. The dB-linear range of the proposed VGAs is extended more than what the approximated exponential equations predict by a bias circuit technique that adopts negative feedback. The proposed VGAs feature wide gain variation, low-power, high linearity, wide control signal range, and small chip size. One of the proposed VGAs is fabricated in 0.18 µm CMOS technology and measurements show a

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... gain variation of 83 dB (-36~47 dB) with a gain error of less than ±2 dB, and P1dB/IIP3 from -55/8 to -20/20.5 dBm, while consuming an average current of 3.4 mA from a 1.8 V supply; the chip occupies 0.4 mm 2 . The other VGA is simulated in 0.18µm CMOS technology and simulations show a gain variation of 91 dB (-41~50 dB), and P1dB/IIP3 from -50/-25 to -33/0 dBm, while consuming an average current of 1.5 mA from a 1.8 V supply. Index Terms -Variable gain amplifier (VGA), automatic gain control (AGC), transceiver, amplifier.