Noise-Shaped Residue-Discharging Delta-Sigma ADCs With Time-Modulated Pulse Feedback

This paper describes a delta-sigma modulator with a new feedback topology in combination with the recently proposed two-step residue-discharging quantizer. Instead of using a single digital-to-analog converter (DAC) with a large number of levels, a mixed-mode DAC is presented which takes advantage of the two-step nature of the quantizer. Hence, only one feedback DAC, which is associated with the coarse bits (MSBs), is required for the modulator and LSBs are fed back as a time-modulated pulse (TMP). Therefore, high quantization resolution is achieved without increasing the front-end DAC complexity. Additionally, a new data weighted averaging (DWA) technique is proposed which not only suppresses the mismatch between the unit elements of the MSB DAC, but also aims to average out the gain error between the MSB and LSB DACs. Therefore, the possible quantization noise leakage is drastically reduced. Detailed mathematical models as well as comprehensive simulation results are provided to prove the efficiency of the proposed structure.