Discrete-time delta-sigma analog-to-digital converter using VCO-based quantizer for IoT applications

Abstract

Low-power systems are essential for Internet-of-Things (IoT) applications powered by harvested energy or batteries, such as wearable devices, structural health monitoring, industrial process monitoring, and personal health monitoring. Analog to digital converter (ADC) is an essential part of the IoT sensor interface and communication system that receives analog signals such as radio waves, light, sound, and biological signals. Depending on the purpose, the ADC is designed for the targets of low voltage operation, dynamic voltage scaling, and high resolution. The technology and supply voltage scaling caused by technological advances reduce voltage headroom and signal power, which makes it challenging to achieve high performance in analog circuit design. A voltagecontrolled oscillator (VCO) based ADC that processes analog information in the time domain can be desirable for technology and supply voltage scaling.However, the conventional VCO-based ADCs present challenges such as dynamic voltage scaling, process variation, narrow input range, and discretetime operation. For high-resolution ADC design, ΔΣ ADC began regaining its popularity as a research topic for high resolution. The discrete-time (DT) ΔΣ ADC effectively reduces two primary noise sources. They are quantization noise and kT/C noise. kT/C noise is more prominent than the quantization noise in high-resolution ADC. kT/C noise is inversely proportional to sampling capacitance and oversampling ratio (OSR). Therefore, high OSR and large capacitance reduce the kT/C noise. Generally, high OSR is preferred to the large capacitance, for the area and power efficiency. However, high-resolution ADC designs are limited in environments where a high OSR cannot be applied.