A survey of voltage-controlled-oscillator-based ΔΣ ADCs

The benefits of technology scaling have fueled interest in realizing time-domain oversampling (ΔΣ) of Analog-to-Digital Converters (ADCs). Voltage-Controlled Oscillators (VCO) are increasingly used to design ΔΣ ADCs because of their simplicity, high digitization, and low-voltage tolerance, making them a promising candidate to replace the classical Operational Transconductance Amplifier (OTA) in ΔΣ ADC design. This work aims to provide a summary of the fully VCO-based ΔΣ ADCs that are highly digital and scaling-friendly. This work presents a review of first-order and high-order VCO-based ΔΣ ADCs with several techniques and architectures to mitigate the nonidealities introduced by VCO, achieving outstanding power efficiency. The contributions and drawbacks of these techniques and architectures are also discussed.