CMOS fully differential operational transconductance amplifier design for delta-sigma modulators

In this paper, we designed four fully differential operational transconductance amplifiers for delta- sigma modulators in 0.35 mum CMOS technology using Mentor Graphics Eldo design tools. We have stated key design techniques for practical implementation of fully differential two stage and single stage operational amplifiers in delta-sigma modulators. Fully differential amplifiers were chosen over single stage amplifiers for their high power supply rejection ratio, 6 dB improvements in dynamic range, good common mode rejection, and rejection of even order harmonic distortion. Important performance parameters for delta-sigma modulators, such as open loop gain, slew rate, settling time, thermal and 1/f noise, output swing, power dissipation, and distortion are investigated and design optimization techniques for the single and two stage amplifiers are presented.