## 1 Introduction
Ultimately, the total amount of PLI currents flowing through the electrodes is multiplied by the impedance imbalance of the electrodes, thus producing the PLI differential voltage drop [25; 26]. This is negatively amplified along with the useful ECG signal, and then must be filtered by analog or digital band-reject filters. EEG signals are generated by the brain because of neural activity. EEG recordings have amplitudes of approximately 10 mV on the cortex and 100 mV on the scalp surface [27]. The latter are challenging to measure due to noise introduced by the electrical grid, electrode movement, and poor contact between the skin and electrode. Applying an impedance-reducing gel to the electrode contact area helps mitigate noise caused by poor contact [28]. The proper selection of the connection cable between the electrode and the system's input circuit (typically an amplification circuit) reduces power line noise at 60 Hz in the EEG signal. Electrodes placed on the scalp capture the electrical activity (potentials) of neurons and are used to record brain activity. Electrode placement typically follows the 10-20 international standard configuration [28; 29; 30]. EEG signals commonly include \(\alpha\), \(\beta\), and \(\delta\) waves, each distinguished by different frequency ranges that vary with the activity level of the cerebral cortex. \(\beta\)-waves have frequencies between 12 and 33 Hz, though they can reach up to 50 Hz [31]. These waves appear when a person is thinking or responding to stimuli and are primarily recorded in the parietal and frontal regions. The \(\alpha\)-waves, with frequencies between 8 and 13 Hz (overlapping the \(\beta\) range), are recorded in healthy individuals who are awake but at rest, with closed eyes, and are primarily located in the occipital region. The \(\beta\)-waves, which range from 4 to 8 Hz, are common in childhood, but may also appear in adults during periods of emotional stress or frustration and are recorded in the parietal and temporal areas. Finally, \(\delta\)-waves, with frequencies below 4 Hz, occur during deep sleep in childhood and in cases of severe organic brain diseases [28; 32; 33; 34; 35; 36]. Other applications for systems developed for biopotential acquisition include the acquisition and processing of surface electromyographic (sEMG) signals, which are used in rehabilitation with robotic prosthetic legs and in the detection and analysis of nerve conduction disorders for diagnosing conditions such as Guillain-Barre syndrome, myasthenia gravis, and bruxism, as well as for controlling prostheses [15; 16; 17; 18; 19; 20]. Electrocardiographic (ECG) signals are also used for clinical diagnosis, providing reliable indicators of the functional and anatomical state of the cardiovascular system [26; 37; 38; 39]. The acquisition of sEMG signals is performed using electrodes placed on the skin over the specific area to be analyzed. For example, when bending or extending the arm, the brain sends signals to the muscles of the upper limb to initiate movement. This information travels from the brain to the muscle fibers via the spinal cord as an electrical impulse [40; 41]. Before reaching the muscle fibers, this impulse passes through a type of neuron called a motor neuron, which is responsible for receiving and transmitting the electrical impulse to the muscle fibers, thereby generating an action potential. Consequently, when one electrode captures the depolarization signal, the other records a resting potential. Thus, the recorded sEMG signal corresponds to the difference in action potentials between the two electrodes. sEMG signals range from 50 \(\mu\)V to 5 mV, with a frequency range of 20 to 120 Hz [42; 43]. The ECG signal acquisition is performed using two or more electrodes placed on the chest at various points, excluding the reference electrode, to obtain the corresponding electrocardiographic leads. The ECG signal has a frequency spectrum of 0.05 to 100 Hz and an amplitude of 0.02 to 5 mV [33; 34; 35].