An ion sensing circuit includes an ion sensing element configured for exposure to an electrolytic solution and control of a sensing current through the ion sensing element according to an ion concentration of the electrolytic solution. The ion sensing circuit further includes a current-to-voltage converter coupled electrically to the ion sensing element for generating a converted voltage from the sensing current. The ion sensing circuit also includes a comparator coupled electrically to the current-to-voltage converter for comparing the converted voltage and a threshold voltage to form a comparison result. In addition, the ion sensing circuit includes a latch coupled electrically to the comparator and the current-to-voltage converter. The latch is configured for sampling the output of the comparator according to a clock signal to generate a digital signal used by the current-to-voltage converter for converting the sensing current to the converted voltage.