## 2 Related Works
A data rate of \(250\,\mathrm{k}\mathrm{b}\mathrm{i}\mathrm{t}\mathrm{/}\mathrm{s}\) and an average power consumption of \(8.1\,\mathrm{\SIUnitSymbolMicro A}\) can be achieved. Due to the duty-cycling, the transmitter has to be active until WuPt is received from WuRx. On the other hand, this affects the latency, reliability, and current consumption of the system. The authors in [30] used a two-stage LNA based on bipolar junction transistors (BJTs) and achieved a sensitivity of \(-90\,\mathrm{d}\mathrm{B}\mathrm{m}\). However, the presented architecture means a higher circuitry effort due to numerous passive components. The average power consumption comes to \(3\,\mathrm{\SIUnitSymbolMicro W}\) and data rate is \(128\,\mathrm{k}\mathrm{b}\mathrm{i}\mathrm{t}\mathrm{/}\mathrm{s}\). The higher data rate is necessary to reach the listening time of the WuRx when using during duty-cycling protocol. Furthermore, the extended active time of transmitter increases the current consumption. In [28], the authors used an additional amplifier stage situated between detection circuit and interrupt generator. The developed circuit with LF-amplification stage based on OAs achieves a sensitivity of \(-55\,\mathrm{dBm}\) with a power requirement of \(1.2\,\mathrm{\SIUnitSymbolMicro W}\). The study does not mention the data rate. In [31], a higher sensitivity of \(-70\,\mathrm{dBm}\) is gained with this approach. The signal is amplified with an OA, and the comparator is used as preamble detector, using an additional microcontroller for address-matching of the WuPt and triggering the MCU in order to process the signal. The high sensitivity is achieved but only for a very low data rate of around \(40\,\mathrm{bit/s}\). Compared to data rate in the range of \(1\,\mathrm{kbit/s}\), the latency and current requirement increases by a factor of 25. On the other hand, in [32; 33], the research study shows a WuRx circuit with LF-amplifier made from two high-gain BJTs. The results provide high sensitivity with an input power of \(-63\,\mathrm{dBm}\) to supply a WuRx with a power of \(8.7\,\mathrm{\SIUnitSymbolMicro W}\) and \(7.4\,\mathrm{\SIUnitSymbolMicro W}\). It has to be noted that these designs are working in the \(433\,\mathrm{MHz}\) band. A slight increase of sensitivity compared to \(868\,\mathrm{MHz}\) can be expected. The presented circuits show a high sensitivity due to the integration of a BJT amplifier based on discrete components integrated between the enveloped detector and the interrupt generator. The authors investigate proposed WuRx circuit performances for wireless sensor networks under laboratory conditions. A reliability study is not provided. It should be noticed that sensitivity, power consumption, and data rate are always a trade-off in terms of performance of the WuRx architecture. Table 1 summarizes the mentioned properties of the approaches from the SoA. Figure 2 shows an overview of the described WuRx architectures based on their power consumption, sensitivity, carrier frequency, and LF amplifiers. It can be seen that WuRx with RF amplifiers [29; 30] achieves sensitivity better than \(-70\,\mathrm{dBm}\) with a power consumption of \(8\,\mathrm{\SIUnitSymbolMicro W}\). However, the integration of the LNA increases the average current consumption and the latency of the system compared to an always-on listening approach. On the other hand, WuRx architectures with voltage or LF amplifier circuit [26; 27; 28] are considered as low power consumption WuRx of less than \(2\,\mathrm{\SIUnitSymbolMicro W}\), where their sensitivity is considered low, in the range of only \(-55\,\mathrm{dBm}\). This suggests a correlation between sensitivity, data rate, and power requirement. Thus, there are trade-offs to be made when designing WuRx architectures. The use of amplifiers in LF range is important to enhance the performance of WuRx without increasing power consumption and decreasing sensitivity and data rate.