High Speed Continuous-Time Sigma Delta A/D Converters
To circumvent the timing-related non-idealities of conventional continuous-time sigma-delta (SD) analog to digital converters (ADCs), semi discrete-time elements like transmission lines (TL) can be used. Up to now, the TL based SD modulators for sampling frequency of several hundred MHz using lengthy off-chip TLs have been successfully designed.
We are currently conducting research towards achieving a fully integrated alternative for the bandpass ADCs. The finite gain bandwidth products of active amplifiers using the standard silicon technologies limit the maximum sampling frequency to bellow 10-20GHz. However, TLs at these frequency ranges have length of several millimeters and suffer from limited quality factor (<5-10) which makes integrating the ADC very challenging. Tunability and achieving a low power integrated solution, which ends up to a reasonable SNR for the modulator are other important factors that are taken into account in this research.
Dr.-Ing. A. Zahabi