## 1 Introduction  
Current-mode electrochemical sensors have been widely used to detect the blood glucose and viruses in the diagnosis of various diseases such as diabetes, hyperlipidemia, and the H5N1 avian influenza virus (AIV) [1, 2, 3]. The early diagnosis of highly pathogenic viruses such as H5N1 AIV is significant for preventing their rapid spread. A current-mode sensing technique using an aptamer-based field-effect transistor with an extended gate was previously introduced to detect AIV [3]. In addition, blood glucose sensing based on the electrochemical current-mode sensors with a potentiostat biasing circuit was reported in [1, 2]. A general sensing mechanism with a three-electrode potentiostat electrochemical current-mode sensor is shown in Figure 1a [4]. For electrochemical current-mode sensors for blood glucose sensing, the level of diabetes can be detected by sensing the current generated through various potential differences according to the change in the concentration of glucose [4, 5]. Glucose or virus concentrations are generally measured using an amperometric electrochemical sensor. A three-electrode structure with a potentiostat consisting of a working electrode (WE), reference electrode (RE), and counter electrode (CE) can measure the current generated by the electrochemical reaction [6, 7]. When we assume a very small voltage drop across the current meter, the voltage difference between the WE and RE can be kept constant by the feedback error amplifier [8]. The current generated by the electrochemical reaction flows from the CE to the WE, and this current is measured by the current meter. Therefore, the potentiostat sensor converts the solution concentration into a current. This characteristic of the sensor is suitable for bio-sensing applications such as blood glucose and virus analyses [9; 10; 11]. The conventional circuit of the current mirror based potentiostat readout circuit is shown in Figure 1b. The \(M_{0}\) and the control amplifier (CA) generate a feedback loop, and the \(V_{REF}\) between WE and RE, which is \(V_{DD}\)-\(V_{DAC}\), is stabilized. The current from the electrochemical sensor, \(I_{SEN}\), is copied by the current mirror, \(M_{1}\) and \(M_{2}\). In this architecture, however, the mismatch between the current mirror transistors due to the process variations and channel-length modulation deteriorates the sensing accuracy. Moreover, the 1/f noise components generated in \(M_{1}\) and \(M_{2}\) act as the main noise contributors. Therefore, designing a current mirror with low-noise [12; 13] and mismatch-tolerant characteristics is critical [14; 15]. In this study, a potentiostat sensing circuit with a low-noise and mismatch-tolerant current mirror is proposed. The chopper stabilization scheme and dynamic element matching (DEM) technique are integrated to reduce the low-frequency noise and mismatch in the current mirror. The gain-boosted cascode scheme is also applied to the current mirror to reduce the mismatch between the drain-source voltages (\(V_{DS}\)) of the current mirror. The mirrored electrochemical current is converted to the output voltage by a low-noise chopper-stabilized transimpedance amplifier (TIA). In previous studies [16; 17], a different chopper frequency and DEM frequency are used, and this may introduce performance degradation due to the intermodulation distortion (IMD) between the chopper and DEM frequencies [18]. The low DEM frequency also requires the lower cut-off frequency of LPF, which consumes a large circuit area. Because the square waveform has odd-harmonics, if the DEM clock and the chopper clock are operated at different frequencies, the interaction between these harmonics can generate IMD, which can degrade the signal quality. As a result, the proposed readout circuit used the same frequency for the chopper and the DEM, therefore minimizing the IMD between the chopper and DEM. Moreover, the relatively higher operating frequency of the chopper and the DEM can relax the area consumption of the LPF.