Patent ID: 8425744

Claim:
An ion sensing circuit comprising: an ion sensing element configured for exposure to an electrolytic solution and control of a sensing current through said ion sensing element according to an ion concentration of the electrolytic solution, said ion sensing element including an ion-sensitive field-effect transistor that comprises, a first end for receiving a sensing voltage of the electrolytic solution that varies according to the ion concentration of the electrolytic solution, a second end electrically coupled to a current-to-voltage converter, and a third end, said second and third ends being configured to permit the sensing current to flow through the ion sensitive field-effect transistor according to the sensing voltage; said current-to-voltage converter coupled electrically to said ion sensing element for generating a converted voltage from the sensing current, and including a capacitor coupled electrically between the second end of said ion sensing element and a ground potential, said capacitor being configured for providing the converted voltage, a current source for providing a reference current, and a first switch connected in series with said current source and comprising a control terminal for receiving a digital signal to control said first switch between conducting and nonconducting states, the converted voltage being varied by the reference current when said first switch is at the conducting state; a comparator coupled electrically to said current-to-voltage converter for comparing the converted voltage and a threshold voltage to form a comparison result; and a latch coupled electrically to said comparator and said current-to-voltage converter, said latch being configured for sampling the output of said comparator according to a clock signal to generate the digital signal, the digital signal being used by said current-to-voltage converter for converting the sensing current to the converted voltage.