## 1 Introduction  
Diabetic status, such as improved hemoglobin A1C levels and reduced long-term microvascular and macrovascular complications, can be detected through a glucose monitoring system [1]. Current mode electrical sensors that detect glucose concentrations have been widely used to detect diabetes [2, 3, 4]. A glucose monitoring system based on electrochemical current mode sensors using a potentiostat biasing circuit was reported in [2, 3]. The sensing mechanism using a three-electrode potentiostat sensor is shown in Figure 1. A general potentiostat circuit consists of a control unit (control amplifier), a measurement unit that measures the sensing current (\(I_{\textit{sense}}\)) according to the impedance of the solution, and three electrodes [5]. The potentiostat control unit operates by maintaining the voltage difference between a working electrode (WE) and a reference electrode (RE) to the desired voltage potential, \(V_{\textit{cell}}\), for which the analyte under study can generate a redox current. The generated redox current flows from the counter electrode (CE) to the WE, or vice versa, and the solution concentration can be monitored by detecting this current. In the case of electrochemical current mode sensors for glucose detection, the level of diabetes can be detected by observing the current generated through a constant potential difference according to changes in the glucose concentration. This characteristic of the current mode potentiostat sensor is suitable not only for glucose monitoring, but also for other biometric applications such as virus detection [6, 7]. Figure 2a shows a typical potentiostat with a single-end (\(SE\)) topology [7; 8; 9]. The negative feedback of the potentiostat ensures that \(V_{cell}\) tracks an applied potential difference \(V_{src}\) under varying current-load conditions. The \(WE\) is indirectly biased to the ground potential by the virtual ground of OP\({}_{3}\). The OP\({}_{1}\) buffers the voltage of the \(RE\), and the negative input terminal of OP\({}_{2}\) is maintained to the ground by the electrochemical feedback loop; thus, the potential of the \(RE\) is maintained at -\(V_{src}\). The voltage swing of \(V_{cell}\) in the \(SE\) topology, \(S_{SE}\), assuming that OP\({}_{2}\) has a rail-to-rail output, is then defined by the voltage swing at the \(CE\):  
\[S_{SE}=|V_{dd}-V_{ss}|\frac{R_{WE}}{R_{WE}+R_{CE}} \tag{1}\]  
where \(V_{dd}\) is the positive supply voltage and \(V_{ss}\) is the negative supply voltage. To maintain the voltage potential between the \(WE\) and \(RE\) by the virtual ground using negative feedback and to extend the allowable voltage swing of the \(V_{cell}\) under a low-supply-voltage condition, the \(SE\) scheme can be expanded to a fully differential (FD) potentiostat scheme, as shown in Figure 2b [10]. The negative feedback of OP\({}_{6}\) ensures that \(V_{cell}\) tracks an applied potential difference, \(V_{src}\), similar to the \(SE\) topology. In the \(FD\) topology, however, assuming that OP\({}_{6}\) has a rail-to-rail output, the voltage swing for the \(FD\) potentiostat \(S_{FD}\) is expressed as:  
\[S_{FD}=2|V_{dd}-V_{ss}|\frac{R_{WE}}{R_{WE}+2R_{sense}+R_{CE}} \tag{2}\]  
Assuming that \(R_{sense}\) is negligible, the \(FD\) potentiostat can double the voltage swing range of the \(SE\) topology. In addition to the improved signal swing, the \(FD\) potentiostat suppresses the common mode noise and doubles the operating range of the sensor's output owing to its differential characteristics. Expanding the voltage swing of the potentiostat using the \(FD\) architecture offers a wider range of voltages for glucose detection. The circuit with a wider output range is required when the supply voltage is lowered or when the output voltage is measured in by the transimpedance amplifier. In addition, the \(FD\) potentiostat may solve the  
Figure 1: Three-electrode potentiostat sensor. Figure 2: (**a**) Single-end topology, (**b**) fully differential topology, and (**c**) fully differential difference topology.