## 1 Introduction  
Continuous monitoring of electrocardiograms (ECG) is used to diagnose cardiovascular diseases, such as cardiac arrhythmias, bradycardia, and paroxysmal supraventricular tachycardia. These diseases cause dizziness, shortness of breath, fatigue, and death [1; 2; 3]. Therefore, users require that the ECG monitoring devices be comfortable and portable for rapid disease detection and convenience. Thus, two-electrode monitoring is more popular than three-electrode monitoring [4; 5; 6; 7]. When the instrumentation amplifier (IA) and human body are connected, power-line interference and noise causes the large common-mode interference (CMI) through the bio-impedance. The generated large CMI causes distortion and saturation of the ECG signal. Therefore, it is important to control large CMI. The ECG recording method to reduce CMI is as follows. As illustrated in Figure 0(a), the three-electrode ECG monitoring uses a two-electrode connection for ECG signal acquisition and a third electrode to bias the body by connecting it to the driven right leg (DRL) to prevent 60-Hz CMI [8; 9]. The two-electrode ECG monitoring is shown in Figure 1b. This monitoring system, while eliminating the third electrode, provides users with better comfort. Although the area was increased in the CMCP added to reduce the CMI, the DRL scheme mainly used in three-electrode recording was not applied. Therefore, the overall area consumption did not increase significantly compared to previous studies. In addition, the number of electrodes is reduced compared to the three-electrode method. Compared to the three-electrode method, the area was reduced in the entire system. However, the ECG signal is saturated by the CMI owing to the removal of the third electrode. This is because the proposed current feedback instrumentation amplifier (CFIA) cannot handle large common-mode input voltages because of the limited operating point of the input transistor. When the input exceeds the power supply range, as shown in Figure 2, the electrostatic discharge (ESD) diodes are turned on, and the signals are saturated. The common-mode charge pump (CMCP) schemes with single comparator to suppress the CMI were reported [4,5]. In these schemes, the switching noise and inter-modulation distortions caused by the CMCP operation can distort the ECG signals. Figure 1: (**a**) Conventional three-electrode ECG monitoring; (**b**) two-electrode ECG monitoring. Figure 2: Two-electrode recording saturated by CMI without CMCP topology. In this paper, the common-mode charge pump (CMCP) with window comparator is proposed. The CMCP can prevent turn-on of the ESD diodes and maintains a constant common-mode range that achieves the CFIA operating point. The charge pump is enabled when the input common mode exceeds the desired common-mode window, which is monitored by the window comparator. If the input common mode is in the desired window, the input signals are not degraded by the charge pump operation. With the CMCP, the ECG input signals can be properly measured without saturation under large CMI conditions. In addition, low-noise characteristics and the high-input impedance for high-accuracy characteristics are very important for amplifying a small ECG signal (1-2 mV) [10,11]. Therefore, we used the CFIA structure to achieve high-input impedance and adopted chopper stabilization in the CMCP loop and CFIA to reduce low-frequency 1/f noise. Recently, wearable platforms including watches, armbands, and disposable patches have shown the capability to capture ECG signals in a convenient and effective way [12]. The ECG signal is one of the most important biophysical signals and can be used for the monitoring of daily activities, emotional states, and cardiovascular diseases. In recent research, the diagnosis systems and various applications based on the accurate classifications of ECG signals using the advanced artificial intelligence (AI) show superior performance [12].