A Highly Digital VCO-based ADC for IoT Applications on Skywater 130nm

This paper proposes a highly digital Analog-to-Digital Converter (ADC) for various internet of things applications, which operates at the bandwidth below 50 kHz. Our goal is a highly digital ADC that can be integrated into the low-power System-on-Chip (SoC) to adapt to IoT demands like audio recording or sensor measuring. The ADC is implemented using only ring-oscillator and digital circuits that is based on time-encoding technique and Delta-Sigma modulation. In this work, we optimize the Voltage Control Oscillator (VCO) for high linearity and apply a Cascaded Integrator Comb (CIC) filter with the aim of increasing the ADC’s resolution. Our work is implemented and verified by fully open-source tools on the Skywater 130 - nm technology. The ADC produces more significant than 12 effective bits at the cost of 0.97 mW and occupies 0.08 mm2.