## 4 Discussion  
Figure 6 shows the transient simulation results of the proposed majority voter system. The three input channels, namely in1, in2, and in3, are three data paths which accept the same data from the front stage. It is assumed that the input channel in1 accidentally introduces an error and is used to represent an input signal which is affected by an SEU. At  
Figure 5: Schematic of **(a)** the designed TMR circuit based on STT-MTJ devices and **(b)** the PCSA circuit.  
three time points, namely 2, 20, and 22.2 ns, the input channel in1 is not able to function normally. For example, it maintains a value of \"0\" when other voters change to \"1\" at the simulation time of 2 ns. As can be seen, the other two input channels share the same signal, representing the \"majority\". So, the output should never be affected by the status of in1. Figure 6 shows that the simulation results are in accord with these analyses. At 2 ns with the CLK at a low level, it is in writing mode and the data should be successfully written into the STT-MTJ device. Therefore, the storage cell should be the same as in2 (or in3) and not be affected by in1. Then, in the following period of time in the reading mode from 7.5 to 15 ns, the output is validated to be \"1\". Similarly, we can also find out that at 22.5 ns, \"0\" derived from the majority in2 and in3 is successfully written into the storage cell and is read out correctly thereafter. This simulation reveals that the output is not affected by the error from in1, and indicates that the designed majority voter based on STT-MTJ devices can realize the correct logic function of TMR.  
Furthermore, the simulation results show that the output can be recovered from the error state when the circuit encounters SEUs. Figure 7 demonstrates the anti-irradiation functionality of the proposed TMR module. According to the data stored in STT-MTJ devices, the sensitive nodes can be represented by Q or \(\
eg\)Q. Here, Q and \(\
eg\)Q are representing the storage of \"1\" and \"0\", respectively. When high-energy particles hit the sensitive nodes under certain radiation levels, the deposited charges can be used to reduce the diverse LET. Since the amplitude of the LET is proportional to the particles' energy, an injected charge \(Q_{inj}\) of 0.2 pC is assumed. In Figure 7a, it is assumed that an SEU which occurred at 10 ns induced an injection of a 0.2 pC charge into the sensitive storage cell. At this time, a high voltage level represented by \"1\" is stored in the sensitive node, which can be verified by the fact that the CLK is low and the three input signals switch from \"0\" to \"1\" at 2 ns. Generally, the injection of negative charge has the ability to toggle the output. Interestingly, the simulation results show that the output only has a slight fluctuation. It is the TMR system that prevents the signal from toggling the wrong output and quickly recovers the correct output. This can be explained by the different charge storage pattern in MTJs. The charge stored in the MTJ devices of the majority voter circuit still has an impact on the sensitive node, while the traditional TMR output is separated from the storage cell by a TG and depends on a clock signal to refresh the sensitive node. Therefore, the MTJ device from the majority voter is able to drag the output back with the help of the PCSA circuit. As a result, the data stored in the sensitive node are recovered. The simulation results of reading \"0\" are shown in Figure 7b. The CLK is low at the time of 25 ns. It is similar to the operation of reading \"1\". As the MTJ devices are still carrying \"0\", the TMR system is able to prevent the signal from toggling and recovers it. All of the SEUs can only induce a small fluctuation in the outputs. The simulations prove that the output can be recovered  
Figure 6: Transient simulation results of the majority voter circuit based on STT-MTJ devices.  
successfully from an SEU in both operations. Therefore, the proposed TMR circuit shows a certain tolerance to SEUs.