A CMOS linear-in-dB VGA and AGC loop for telecommunication applications

In this paper, an Automatic Gain Control (AGC) loop which is based on a linear-in-dB Variable Gain Amplifier (VGA) is proposed. The VGA structure is based on simple nMOS differential pairs with variable tail currents. The linear-in-dB gain tuning schema is designed using a novel exponential current generator which also offers temperature compensation of the VGA's gain. The gain of the VGA is tuned by a control voltage with gain range about 28dB with Â?1dB linearity error. The worst cases of the VGA gain, over process and temperature corners, are Â?1.54dB and Â?2.45dB for maximum and minimum gain setting, respectively. The proposed implementation is designed in a CMOS 90nm triple-well process with 1.2V supply voltage.

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