Real Comparator Behavior and Its Effect on Wake-Up Receivers

Wake-up receivers (WuRxs) enable low-latency wireless communication with power consumption three orders of magnitude lower than that of conventional RF receivers. Most WuRxs based on commercial off-the-shelf components rely on a comparator to digitize the analog LF signal. The comparator is the central component that determines achievable sensitivity, range, and energy efficiency. High input offset voltage or large hysteresis increase the required signal amplitude and therefore degrade the minimum detectable signal (MDS). This work presents detailed measurements of comparator trip levels for eight devices, providing realistic values for input offset and hysteresis. Based on these measurements, formulas are derived to estimate the WuRx sensitivity from the comparator parameters and the envelope-detector voltage sensitivity. The results show that increasing the common-mode voltage can improve the sensitivity by up to 1.8 dB. Two comparators not previously used in WuRxs were evaluated. The ISL28915 achieves the lowest MDS of -48 dBm at only 500 nA supply current, making it suitable for always-on WuRxs. The MAX9075 offers low propagation delay and a supply current of 3 µA, providing a clear improvement over the TLV3201 previously used in duty-cycled WuRxs. These findings provide practical design guidance for comparator selection and enable improved sensitivity in future WuRx implementations.