## 1 Introduction  
In recent years, the monitoring of physiological parameters of the human body has increased, where biopotential signals can directly reflect the physical condition and the health status of an individual [1]. Biopotential signals are increasingly being applied to real-time health monitoring, disease diagnosis, rehabilitation device control, brain-computer interfaces, neuroscience, cognitive psychology, and artificial intelligence research, among others [2, 3]. In general, biopotential signals, such as electrocardiogram (ECG), surface electromyography (sEMG), electroencephalogram (EEG), and electrooculogram (EOG) signals, are characterized by high impedance, low frequency, low amplitude, and strong background noise [4]. When a biopotential signal is recorded, the target/result of the recordings is almost completely submerged by the background noise/interference inherent in the recordings, as the signal is usually characterized by a low amplitude [5, 6]. Therefore, these noises/interferences mainly fall into the following three categories: first, power line interference, which is composed of a 50 Hz or 60 Hz frequency and its harmonics, commonly defined as electromagnetic noise produced by power supply circuits and electronic equipment [7]; second, motion artifacts, which are caused by poor contact between the electrodes and an individual's skin surface [8], or as a result of wire movement between the electrodes and the amplifier [9]; and third, physiological artifacts in the form of other signal(s) recorded along with the originally desired biopotential signals [10; 11]. Several methods have been proposed to remove the previously described interference/noise from a biopotential signal of interest. To this end, most methods have focused on improving hardware circuitry and using software filtering techniques [12; 13; 14]. Many hardware-based methods exist to minimize the interference inherent in biopotential signal recordings, such as twisting the input cables to reduce the area of the loop formed by the cables [15] or making the acquisition devices rely on batteries (direct current) for power [16]. The adoption of a high common-mode rejection ratio amplifier, a driven right-leg circuit, active electrodes, and isolation can further suppress interference [17; 18; 19]. Shielded technology is also one of the most widely used hardware methods for suppressing power line interference. The most popular shielded technology is the use of a small coaxial cable, in which the outer layer is connected to a certain type of conducted signal to prevent the signal of the inner cable from being contaminated by extraneous interference. [PERSON] showed that unshielded electrodes are responsible for most of the power line interference, and that shielding the electrodes, together with the conducted right leg, is quite effective in reducing such interference [20]. The human body is a volumetric conductor that collects interference currents like an antenna [21]. The electrical grid is the main source of interference currents. The capacitance between the body and ground (neutral wire) is considered to be about 200 pF. The coupling capacitance to the live wire is usually about 2 pF [21; 22]. Maximum values of these parasitic capacitances have been measured as high as 4 nF and 5 pF [23; 24]. These capacitive couplings conduct a power line interference (PLI) current of nearly 200 nA, which flows through the body to the ground. The PLI currents pass partially through the electrodes directed to the ground signal electrode of the amplifier. Therefore, bioamplifiers with a high common-mode rejection ratio (CMRR) are needed to avoid a voltage drop at common-mode input impedances. The unshielded conductors are a kind of antenna that collects PLI currents. At the highly insulated front ends, electrodes are passed in the direction of the ground through the body's capacitance.