Design of a Wideband Variable-Gain Amplifier With Self-Compensated Transistor for Accurate dB-Linear Characteristic in 65 nm CMOS Technology

A simple yet effective approach for variable-gain amplifier (VGA) design with accurate dB-linear characteristic is presented. In order to extend the bandwidth of the designed VGA with a minimized footprint, an inductorless-based approach is adopted. Moreover, a unique approach that exploits a self-compensated transistor to compensate dB-linear gain error is proposed. Consequently, the overall VGA has an accurate dB-linear inherent characteristic without using any additional exponential generator for gain control. To prove the concept, the designed VGA is fabricated in a standard 65 nm CMOS technology. The measured results show that the voltage gain of the designed VGA can be controlled from -19 dB to 21 dB with a gain error less than 1 dB. Meanwhile, more than 4 GHz of bandwidth can be achieved for the entire gain range. The power consumption of the VGA, excluding the output buffer, is 3.9 mW. The core circuit of this design only occupies an area of 0.012 mm(2).