# A Novel Battery-Supplied AFE EEG Circuit Capable of Muscle Movement Artifact Suppression
## 4 Simulation and Results: Comprehensive Analysis
### Simulation of Novel EEG-B3V3S/C1 Circuit Design
#### 4.1.1 Simulation in a 50 Hz Electrical Grid Environment
The muscle artifacts remaining in the output of the EEG circuit (V\({}_{\text{out}}\)--blue) produce low frequency sine-like waves like the one shown in Figure 19, which nonetheless still carry all the important information of the ground truth EEG signal (V\({}_{\text{eeg}}\)--red) (it resembles the phenomenon of signal modulation). Indeed, the strong muscle compound movement artifacts are severely suppressed and do not influence the measurement capability of the proposed EEG-B3V3S7C1 circuit, as it will become clear in the following subsection, where it becomes apparent that the remaining noise artifacts do not forbid the detection of alpha and beta wave peaks in the Fourier plane. By looking closer at Figure 20, several facts about the morphology of the EEG signal can be observed. The ground truth EEG signal (V\({}_{\text{eeg}}\)--red) represents the component of the brain signal that is collected by the electrodes of the EEG circuit. In order to visualize it in the image, the raw ground truth EEG signal (V\({}_{\text{eeg}}\)--red) is magnified 300 times, in order to be of the same order of magnitude as the actual raw EEG channel 1 signal (V\({}_{\text{chl}}\)--gold) that is collected by the electrodes, offering an indirect quantitative measurement of gain derived for the figure. It contains the slower but bigger in amplitude alpha wave component from approximately 0.3 s to 0.8 s, as well as some faster lower amplitude beta and gamma wave components. Noteworthy is the segment in the region of around 0.8 s, where a higher frequency ERP phenomenon of around 3 kHz is depicted. The raw EEG reference channel signal (V\({}_{\text{chl}}\)--gold) is the one from the electrode that carries the brain red signal, while the raw EEG reference channel signal (V\({}_{\text{chr}}\)--purple) is the one from the reference electrode. The morphology of those waveforms validates the proper functionality of the proposed signal generator circuitry, because it accurately depicts EMI noise and muscle artifacts that have contaminated the raw EEG brain signal. More precisely, EMI is the higher frequency component of the purple and gold waveforms at around 60 mVpp and the slower but rather higher amplitude component of the waveforms that carries on top of it. The EMI noise is the one that relates to muscle movement artifacts (i.e., EMG, EKG, EOG) that the electrodes collect. The output of the EEG circuit (V\({}_{\text{out}}\)--blue) is the output of the overall EEG circuit. It takes the raw EEG reference channel signal (V\({}_{\text{ch1}}\)--gold) and magnifies it by 300 V/V, as was theoretically expected, validating with a graphical quantitative measurement the accuracy of the design. Moreover, it achieves an extreme reduction in both the EMI noise and the muscle artifacts. Making a quantitative assessment of the noise suppression, instead of being magnified 300 times, the EMI is hardly inspectable in the output signal (V\({}_{\text{out}}\)--blue), and the muscle artifacts are magnified approximately only 2 times. This ensures that this novel design successfully suppresses EMI and muscle noise artifacts, ensuring satisfactory EEG signal acquisition. * Simulation at 50 Hz Electrical Grid Environment at the Fourier's Spectrum Subsequently, FFT was performed in the time domain produced by the transient analysis of the simulation (at 50 Hz) to generate the waveforms in the Fourier plane (ina range from 4 Hz to 30 Hz). The frequency response of waveforms in the Fourier plane gives valuable insights into the simulated functionality and performance of the circuit. As depicted in Figure 21, the raw EEG reference channel signal (V\({}_{\text{chref}}\)--green) waveform is the voltage measured at the reference electrode. The raw EEG channel 1 signal (V\({}_{\text{ch1}}\)--blue) waveform is the voltage measured at the channel 1 electrode. The ground truth EEG signal (V\({}_{\text{eeg}}\)--pink) waveform depicts the EEG ground truth signal contained in channel 1.