VCO-ADC Resolution Enhancement Using Maximum Length Sequences

This paper shows how to enhance the resolution of a VCO based ADC by transforming a ring oscillator into a continuous-time maximum length sequence generator. The code spreading provided by the maximum length sequence can be decoded after sampling by a look up table. Compared to an M tap ring oscillator, an equivalent maximum length sequence generator enhances the resolution of the resulting ADC by a factor 2 M /M. We derive the basic system analysis for this new ADC architecture and show a simulation example.