Ultra low-voltage and low-power dB-linear V-I converter using composite NMOS transistors

In this paper, an ultra low-voltage and low-power exponential V-I converter is developed, using Taylor series expansion for realizing the exponential characteristics. The new CMOS exponential V-I converter is based on the composite NMOS transistors. The newly proposed approximation function based on Taylor's concept is used to extend the dB-linear output current range. In a 0.25 /spl mu/m CMOS process, the simulations show more than 20 dB output current range and 18 dB-linear range with the linearity error less than /spl plusmn/0.5 dB. The average power dissipation is less than 50 /spl mu/W at /spl plusmn/1 V supply voltage. The proposed EVIC can be used for the design of an extremely low-voltage and low-power variable gain amplifier (VGA) and automatic gain control (AGC).