A CMOS pseudo-exponential current-output DAC with code-dependent body-biasing

In this paper, a nonlinear current-output digital to analog converter (DAC) employing a pseudo-exponential transconductance amplifier is presented. The proposed transconductance amplifier makes use of the code-dependent body-biasing to realize the exponential relationship of the output current to the input digital signal in the CMOS technology. A digital control unit is designed to provide a linearly code-dependent voltage to feed into the transconductance amplifier by charging a capacitor for a period determined by a counter which is loaded by the input digital code. The proposed DAC is simulated in a 180 nm standard CMOS technology. The accuracy of the exponential input-output characteristic is verified by the curve fitting of the simulation results where R-squared value of the fitted functions is greater than 0.999 in all process and temperature corners. The presented DAC consumed 79 μW in the worst-case.