Patent ID: 6657269
Filing Date: 2003-12-02
Classification: G01N

Abstract:
A sensor cell comprising a thin film transistor, a reference capacitor coupled to a gate electrode of the thin film transistor, a sample electrode coupled to the gate electrode of the thin film transistor and arranged to receive a sample for identification, the reference capacitor and the sample electrode providing in combination, a capacitance divider circuit coupled to the gate electrode of the thin film transistor, a further transistor for affording a voltage pulse to the gate electrode of the thin film transistor, the voltage pulse having an amplitude arranged to maintain the thin film transistor in a non-conducting condition and to bias the thin film transistor to a point on its operating characteristic where it is ready to switch from the non-conducting condition to a conducting condition; and means for providing an excitation pulse to the gate electrode of the thin film transistor via the capacitance divider circuit, thereby to switch the thin film transistor from the non-conducting condition at the point on its operating characteristic to a conducting condition, whereby in use of the sensor cell, the output current of the thin film transistor is dependent upon the value of capacitance at the sample electrode arising from receiving the sample for identification.