Method and apparatus for measuring an unknown capacitance using a known reference capacitance
First Claim
1. A method of measuring a capacitance of a capacitor, the method making use of a reference capacitor having a reference capacitance in addition to the capacitance of the capacitor to be measured, the reference capacitor and the capacitor to be measured each having first and second electrodes on opposite sides thereof, the method comprising the following steps:
- (a) precharging a second electrode of a first one of the capacitors to a first predetermined potential, said first capacitor having its first electrode connected to ground;
(b) charging the first electrode of the second one of the capacitors to the same potential as the second electrode of the first capacitor without changing the potential on said second electrode of the first capacitor;
(c) electrically connecting the first electrode of the second capacitor to the second electrode of the first capacitor so that the potential on the second electrode of the first capacitor is equal to the potential on the first electrode of the second capacitor, and switching the potential on the second electrode of the second capacitor between a first predetermined value and a second predetermined value; and
(d) comparing the potential on the second electrode of the first capacitor with a reference potential, disconnecting the first electrode of the second capacitor with the second electrode of the first capacitor and iterating above steps (b) and (c) until the potential on the second electrode of the first capacitor passes through a level corresponding to the reference potential, and counting the number of iterations, said number of iterations being indicative of the ratio of capacitance between the two capacitors and consequently of the capacitance of the capacitor to be measured when the reference capacitance is known.
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Abstract
A method and apparatus for measuring an unknown capacitance using a known reference capacitance, wherein a first electrode of the unknown capacitance is connected to ground. The apparatus includes a first device for precharging the unknown capacitance to a first predetermined potential; a second device for selectively charging a first electrode of the reference capacitance to the same potential as the second electrode of the unknown capacitance, without changing the potential on the second electrode of the unknown capacitance; a first switch for selectively electrically connecting the first electrode of the reference capacitance to the second electrode of the unknown capacitance; a third device for switching the potential on the second electrode of the reference capacitance between a first predetermined value and a second predetermined value; a comparator for comparing the potential on the second electrode of the unknown capacitance to a reference voltage; and a sequencer responsive to the output from the comparator and designed to control the second device, the first switch, and the third device, and for counting the number of times these devices are used. The number of times these devices are used in a particular measuring operation according to the present method, is indicative of the unknown capacitance.
40 Citations
32 Claims
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1. A method of measuring a capacitance of a capacitor, the method making use of a reference capacitor having a reference capacitance in addition to the capacitance of the capacitor to be measured, the reference capacitor and the capacitor to be measured each having first and second electrodes on opposite sides thereof, the method comprising the following steps:
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(a) precharging a second electrode of a first one of the capacitors to a first predetermined potential, said first capacitor having its first electrode connected to ground; (b) charging the first electrode of the second one of the capacitors to the same potential as the second electrode of the first capacitor without changing the potential on said second electrode of the first capacitor; (c) electrically connecting the first electrode of the second capacitor to the second electrode of the first capacitor so that the potential on the second electrode of the first capacitor is equal to the potential on the first electrode of the second capacitor, and switching the potential on the second electrode of the second capacitor between a first predetermined value and a second predetermined value; and (d) comparing the potential on the second electrode of the first capacitor with a reference potential, disconnecting the first electrode of the second capacitor with the second electrode of the first capacitor and iterating above steps (b) and (c) until the potential on the second electrode of the first capacitor passes through a level corresponding to the reference potential, and counting the number of iterations, said number of iterations being indicative of the ratio of capacitance between the two capacitors and consequently of the capacitance of the capacitor to be measured when the reference capacitance is known. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20)
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21. Apparatus for measuring a capacitance of a capacitor using a reference capacitor having a reference capacitance, comprising:
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precharging a second electrode of means for precharging a first one of said capacitors to a first predetermined potential, said first capacitor having a first electrode connected to ground; charging means for selectively charging a first electrode of a second one of said capacitors to the same potential as the second electrode of the first capacitor, without changing the potential of the second electrode of the first capacitor; connecting means for selectively electrically connecting the first electrode of the second capacitor to the second electrode of the first capacitor; potential changing means for switching the potential on the second electrode of the second capacitor between a first predetermined value and a second predetermined value; comparator means for comparing the potential on the second electrode of the first capacitor to a reference potential; and sequencer means responsive to the output from the comparator means for controlling the charging means, the connecting means, and the potential changing means, and for counting the number of times each is used. - View Dependent Claims (22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32)
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Specification