## 4 Investigation Results
### Energy Consumption  
The energy consumption of the WuRx mainly depends on the operating mode such as wake-up period and amount of data, as well as the used circuit elements. The length of the active time depends on the data rate and the amount of data. The data rate for the WuPt is 1160 kbit/s at a signal frequency of 18.7 kHz and with Manchester coding. The number of bits and the length of the WuPt are displayed in Table 3. Results show that the total duration of the WuPt (\(t_{\text{WuPt}}\)) is about 27.7 ms.  
During the transmission of a WuPt, the energy consumption of the node depends on the active mode of the components. \(P_{\text{MCU}}\) and \(P_{\text{RF}}\) are the power consumption of microcontroller and RF transceiver during transmission mode. With \(t_{\text{WuPt}}\), the energy consumption is \(E_{\text{TX\_WuPt}}\), as expressed in Equation (3). Figures 15 and 16 show the power consumption of BJT and TIA according to the installed components and working mode. In listening mode, the OA of the TIA board consumes the most current compared to the other components, while for the BJT, the AS3933 has the highest amount of current consumption.  
Table 4 shows the results of the current consumption of the WuRx using the BJT and the TIA amplifiers. These results have been calculated based on Equations (1)-(3) shown in Section 3.2. This includes the different working modes such as listening, receiving, and transmission for a wake-up period of 1 s. Results show that typically the listening mode is characterized with the highest energy consumption of more than 15 times compared to other working modes. Furthermore, it can be seen that the BJT amplifier leads to a lower energy consumption compared to TIA of around 1.7 uj and 0.24 uj in the listening and the receiving mode, respectively. In the transmission mode, both architectures consume about 1.91 mJ. This can be explained by the high current requirement of the SPSGRFC-868 radio module when sending the packets in the range of 21 mA, so that the power requirement of the amplifiers can be neglected.  
The BJT architecture has a lower energy consumption than TIA in listening mode, whereas in active states, both PCBs require nearly the same energy. Figure 17 displays the current waveforms of the transmitting mode, receiving mode with BJT, and receiving mode with TIA, respectively.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Mode** & **TIA** & **BJT** \\ \hline Listening \({}^{\star}\) [μ] & 28.35 & 25.05 \\ Receiving [μ] & 1.52 & 1.28 \\ Transmission [m] & 1.91 & 1.91 \\ \hline \hline \end{tabular} \({}^{\star}\)\(t_{\text{I}_{\text{I}_{\text{I}_{\text{I}_{\text{I}_{\text{I}_{\text{I}_{\text{I}_{ \text{I}_{\text{I}_{\text{I}_{\text{I}}}}}}}}}}}}}\) = 1 s.  
\end{table}
Table 4: Energy consumption of BJT and TIA amplifiers.  
Figure 17: _Cont._  
The energy consumption reaches its maximum in the transmitting mode, where the current consumption reaches a value higher than 15 mA during 27 ms. The current consumption on the transmitter is related to transmitting power of 11 dBm of SPSGRFC-868 radio module, which is lower than the specified current consumption of the data sheet. The measured current is lower than specified in the data sheet because of ASK modulation with a duty-cycle of around 50%.  
Figure 17b,c (BJT and TIA, respectively) show the signal progression at the receiver architectures. Their peak of consumption is related to the MCU, which is waking up. It can be seen also that based on Figure 17c, the signal of the TIA amplifier is very distorted, which is mainly related to AS3933. Since the LF wake-up IC is always ON and listening to the channel, the LDO is very noisy. It refers to the amount of ripple on the output coming from ripple on the input. Due to the measurement inaccuracy of the oscilloscope, the current values of Figure 17b,c are different from the calculations. Here, the effects of the RC constant are clearly visible, whereas in Figure 17a, they are not visible due to the larger measuring range in the mA range.