The present invention relates to an
electronic circuit and an array of such circuits for precisely measuring small amounts or small changes in the amount of charge,
voltage, or electrical currents. One embodiment of the present invention provides an
electronic circuit for measuring current or charge that can be used with a variety of sensing media (including
high impedance sensing media) that produce a
signal by either charge or current production or induction in response to
physical phenomena occurring within the sensing media. In another embodiment, the
voltage level (bias) of either the sensing or
reference electrode can be switched relative to the other upon
receipt of a triggering pulse. This changes the polarity of the
electric field to cause charge of the opposite polarity to be driven to the sensing
electrode, thereby eliminating the need to electrically connect a
discharge path to the sensing
electrode to clear the charge accumulated at the sensing
electrode. This can be supplemented by capacitively
coupling a compensation
signal to the sensing electrode to cause the
amplifier output
signal to lessen in magnitude below a threshold level that permits additional charge or current measurements of the same polarity before performing bias reversal. Alternately or in combination with bias reversal and capacitive compensation, sensor performance can be improved by minimizing inaccuracies caused by leakage currents or current drawn from the sensor. Other described methods of reducing leakage currents that can be used alone or in combination with the aforementioned features include the use of guard rings, physical switches or relays, the controlled creation of charges or currents of a specific polarity in a specific region of the sensing medium, controlled leakage over the surface of an insulator, and controlling the environment in which the circuit operates.