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 mu m 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.