Near threshold RF-only analog to digital converter

This paper describes an analog-to-digital converter (ADC) capable of operating in a RF-only circuit topology. A major limitation to direct RF-powered sensors are the lack of analog circuits. The proposed architecture is comprised of a cross-coupled pair of inverters, which act as the comparator for the ADC. This setup has been simulated in IBMs 0.13 μm bulk CMOS process for a 3 bit analog-to-digital converter (ADC). At a RF supply voltage of 300 mV_RMS and frequency 13.57 MHz, the ADC has a resolution of 20 mV and can resolve voltages ranging from -80 mV to 80 mV, and at a frequency of 915 MHz the ADC can resolve voltages ranging from -140 mV to 140 mV. In order to optimize the ADC operation, the sampling time has been adjusted to one-third of the evaluation time, to give the comparator enough time to complete the amplification.