Measurement of electromagnetic field immunity of voltage-controlled oscillator-based analog-to-digital converters in 28 nm CMOS technology

Internet-of-Things (IoT) devices are compact and low power. A voltage-controlled oscillator (VCO)-based analog-to-digital converter (ADC) benefits from scaled CMOS transistors in representing analog signals in the time domain and therefore meets those demands. However, we find the potential drawback of VCO-based ADCs for the electromagnetic susceptibility (EMS) to RF disturbances that are essentially present in an IoT environment. It is exhibited that the single and even differential designs of VCO-based ADC suffer from the EMS by RF disturbance, which behaves differently from the known common-mode noise rejection. A 28 nm CMOS 11-bit VCO-ADC prototype exhibits sensitivity against RF signals in the widely used 2.4 GHz frequency band.