A 0.96-mW dB-Linear Variable Gain Amplifier With 0.4-dB Linearity Error Over a 62.4-dB Gain Tuning Range

This letter presents a low-power dB-linear variable gain amplifier (VGA) with a small linear-in-dB error over a wide gain tuning range. An exponential current ratio is realized in the linear-in-dB control circuit based on the subthreshold I–V characteristic. The VGA is built with subthreshold common-gate transistors as current steering, accurately replicating the exponential current ratio and forming a tunable gain. Implemented in 55-nm CMOS technology, the proposed VGA occupies a compact active area of 0.011 mm2 excluding the buffer. It achieves a linear-in-dB error of 0.4 dB over a gain tuning range of 62.4 dB, corresponding to the state-of-the-art relative error of 0.6%. The proposed design shows constant 80-MHz bandwidth with a power consumption of 0.96 mW.