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 28 dB with 71 dB linearity error. The worst cases of the VGA gain, over process and temperature corners, are 71.54 dB and 72.45 dB for maximum and minimum gain setting, respectively. The proposed implementation is designed in a CMOS 90 nm triple-well process with 1.2 V supply voltage. & 2012 Elsevier Ltd. All rights reserved.