Patent ID: 7368917

Claim:
An electronic circuit for ion sensors with the body effect reduction comprises: a bridge-type readout circuit, provided with an input terminal and an output terminal, and with an Ion-sensitive field effect transistor (ISFET) having a reference electrode coupled to a ground terminal, wherein one terminal of the ISFET is coupled to the output terminal for outputting the voltage dependent on ion concentration, the bridge type readout circuit further comprises: a first amplifier, wherein its negative input terminal is coupled to a drain of the ISFET and its output terminal is coupled to a source of the ISFET; a first resistor coupled between the input terminal of the bridge sensing circuit and the positive input terminal of the first amplifier; a second resistor coupled between the positive input terminal and the output terminal of the first amplifier, wherein the voltage division of the first and second resistors determines the operating voltage of the ISFET; and a third resistor coupled between the negative input terminal of the first amplifier and the drain of the ISFET; wherein the first amplifier, the first resistor, the second resistor, the third resistor, and the ISFET construct a bridge network to make the ISFET operate under a condition of constant current and constant voltage; a current mirror coupled to the bridge-type floating source circuit, which consists of a first transistor and a second transistor for providing a current to the bridge-type floating source circuit; a third transistor connected to the current mirror, for receiving the operating current identical to the current provided for the ISFET; and a differential amplifying circuit, wherein one input terminal of the amplifying circuit is input with a reference voltage, and the other input terminal is coupled with the output of the bridge-type readout circuit, to generate a differential voltage to the input terminal of the bridge-type-readout circuit, thereby enabling the ISFET to operate under condition of constant current and constant voltage.