An ultra low voltage Sigma Delta modulator with inverter based scalable amplifier

In this paper, a low voltage, second order, switched capacitor Sigma Delta modulator with a novel fully differential amplifier is presented. The immunity to variations with process corners and temperature can easily be achieved, thus maintaining the effective number of bits throughout the entire input signal band. In order to validate the principle, in the ultra low voltage environment, the modulator was designed and tested for the voice band input signals. The circuit was designed using a triple well standard CMOS process, with typical threshold values, without any internal voltage boosting circuits and it is intended for speech applications.