Performance Improvement of an Asynchronous Sigma - Delta Modulator by Programmable Hysteresis

We have investigated the impact of circuit limitations on the design of an Asynchronous Sigma-Delta Modulator (ASDM). Specifically, the hysteresis, which is normally embedded during the quantization process, can be used to improve the performance of ASDM. A programmable hysteretic element was designed and implemented for the quantizer and tested in an ASDM circuit based on John G. Harris et. al. We have shown that modulating the hysteresis in the quantizer can provide a larger input frequency range and save power for low-frequency signal conversion. This circuit converts signals up to 2MHz and 83% of the switching power is saved by switching to a larger hysteresis mode at low frequencies. By following the Harris structure, the design eliminates the op-amp based structure, which is also considered a significant bottleneck for energy efficiency in ADC implementations. The circuit was designed in AMI’s 0.6μm 5-V process.