Patent ID: 6414318
Filing Date: 2002-07-02
Classification: G01J,G01R

Abstract:
An electronic circuit for measuring charge, voltage or current, comprising:(a) input circuit elements configured for sensing charge, voltage, or current to provide an output signal which is a function of the charge, voltage or current being measured wherein said input circuit elements comprise a transistor whose gate is electrically connected to the source of said charge, voltage, or current; (b) amplification circuit elements connected to said input circuit elements and configured for amplifying said output signal to provide said measurement; and (c) measurement control circuit elements configured for measuring said charge, voltage, or current without a continuous discharge path being coupled to at least said input circuit elements; further comprising charge removal elements coupled to at least said measurement control circuit elements wherein said measurements are accomplished with said measurement control circuit elements performing removal of accumulated charge from sensing elements in said input circuit and wherein said charge removal is not continuous; wherein said circuit further comprises circuit elements coupled to at least said charge removal elements and configured for controlling said charge removal; wherein charge of an opposite polarity to the charge accumulated on said sensing elements is controllably induced in or around said sensing medium in order to neutralize the charge on said sensing elements; and wherein said measurement control circuit elements comprise at least two circuit elements selected from the group consisting of: (i) a guard element in association with said sensing element and configured to minimize leakage to said sensing element; (ii) a charge pump circuit comprising a transistor coupled to said sensing element and configured for charge removal from said sensing element; (iii) a charge pump circuit comprising a physical switch coupled to said sensing element and configured for charge removal from said sensing element; (iv) a voltage reset circuit comprising a transistor coupled to said sensing element and configured for charge removal from said sensing element; (v) a voltage reset circuit comprising a physical switch coupled to said sensing element and configured for charge removal from said sensing element; (vi) a compensating current source circuit coupled to said sensing element and configured to reduce said voltage, current or charge below a level which permits additional measurements to be taken, (vii) duplicate circuit elements which are used to measure interfering currents and additional circuit elements coupled to said duplicate circuit elements which are configured to remove said interfering currents from said output signal; (viii) circuit elements configured for controllably capacitively coupling charge to said sensing element; (ix) circuit elements configured for reversing the polarity of the electric field acting in association with a portion of said sensing element to bring charge of the opposite polarity to the sensing element; or (x) circuit elements configured for inducing conductivity in or on an otherwise insulating material connected to said sensing element to bring charge of the opposite polarity to the sensing element.