## 4 Conclusions  
This paper proposes a low-noise and low-power readout IC for two-electrode ECG recording using CMCP for robust CMI. In the two-electrode ECG measurements, it is important to reduce CMI. In this study, it was effectively reduced using a CMCP with a window comparator.  
The proposed readout IC comprises a CMCP stage, amplifying stage, and sub-blocks in a single chip. The CMCP stage comprises switched capacitors, CMCP control logic, and a window comparator. The window comparator compares the input CMI with the reference voltage and transfers it to the CMCP control logic. Using the transmitted comparator output, a constant common-mode range is maintained through the control logic and switched capacitors. The amplification stage comprises a floating HPF, chopper-stabilized CFIA, and QRS peak detector. The floating HPF reduced the DC offset, the CFIA amplified the ECG signal, and the chopper-stabilization technique reduced the 1/f noise. The sub-blocks included the current/voltage reference, timing generator, 2 MHz oscillator, and SPI.  
The proposed readout IC was fabricated by implementing a TSMC 0.18 \(\upmu\)m CMOS process with an active area of 856 \(\times\) 1523 \(\upmu\)m. It achieved a CMI tolerance of 20 V\({}_{\text{PP}}\) at 60 Hz and consumed 23.83 \(\upmu\)W of power at a 1.8 V supply voltage. The input-referred noise was 119 nV/\(\surd\)Hz at 1 Hz and 57 nV/\(\surd\)Hz at 1 kHz. The integrated noise in the ECG signal band (1-100 Hz) was 0.59 \(\upmu\)V\({}_{\text{RMS}}\). The ECG signals were clearly obtained through measurements using the proposed circuit and achieved CMI tolerance of 20 V\({}_{\text{PP}}\) at 60 Hz. The proposed circuit with low-noise and CMI tolerance characteristics is suitable for two-electrode ECG recordings.  
The main directions for future research are as below. This gain of the IA in this IC is fixed; however, in the real applications, including clinical or wearable platforms, the amplitudes of the ECG signals can show individual differences, and the high programmability for gain and bandwidth of the IA are required. In addition, since the CMRR characteristics are degraded because of electrode impedance mismatch, additional CMRR enhancement is required. Finally, additional measurements are needed by fabricating a small module for portable long-term recording.  
Conceptualization, K.N. and H.K.; methodology, H.K.; software, K.N.; validation, G.C., S.K. and B.J.; formal analysis, H.K.; investigation, M.Y. and H.S.; resources, H.K.; data curation, K.K.; writing--original draft preparation, K.N.; writing--review and editing, K.N.; visualization, K.N.; supervision, H.K.; project administration, H.K.; funding acquisition, H.K. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the Practical Technology development medical microrobot Program (R&D Center for Practical Medical Microrobot Platform, HI19C0642) funded by the Ministry of Health and Welfare (MOHW, Korea) and the Korea Health Industry Development Institute (KHIDI, Korea). This research was supported by the MSIT (Ministry of Science and ICT), Korea, under the ITRC (Information Technology Research Center) support program (IITP-2021-2017-0-01635) supervised by the IITP (Institute for Information & Communications Technology Planning & Evaluation). This work has supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No.2022R1A2C100517011). This work is also supported by ABOV semiconductor, Inc.  
Not applicable.  
The chip fabrication and EDA tool were supported by the IC Design Education Center (IDEC), Korea.  
The authors declare no conflict of interest.